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Last Updated :2024/11/01

研究者情報

マスター

アカウント（マスター）

  • 氏名

    小関　成樹(コセキ　シゲノブ), コセキ　シゲノブ

所属（マスター）

  • 農学研究院　基盤研究部門　生物環境工学分野

所属（マスター）

  • 農学研究院　基盤研究部門　生物環境工学分野

独自項目

syllabus

  • 2021, 食品・循環農業システム工学特論, Advanced Food and Bioproduction Engineering, 修士課程, 農学院, 農業生産技術、食品加工、ポストハーベスト、バイオマス資源、持続可能型農業、環境影響
  • 2021, 食品加工工学特論, Advanced Food Process Engineering and Technology, 修士課程, 農学院, 食品，総合技術監理，リスクアナリシス，ＨＡＣＣＰ
  • 2021, 食資源生産論, Production in Global Food Resources, 修士課程, 国際食資源学院, 作物，畜産物，水産物，GAP, バイオテクノロジー，発酵生産，食の安全，HACCP, 機能性食品，健康，エネルギー
  • 2021, 農学フロンティア総論, Advanced Review of Agriculture Frontiers, 修士課程, 農学院, 農学の最先端研究、食品、バイオマス、エネルギー、水土資源、農業経済、持続的生産、生物共生
  • 2021, 食品安全・機能性開発学特論, Advanced Safety and Function of Food, 修士課程, 農学院, 食品安全性、予測微生物、食料確保と安全性、植物由来機能性食品、微生物由来機能性食品、腸内細菌叢の改変に基づいた機能性食品、食肉由来機能性食品
  • 2021, 食品安全・機能性開発学特論演習, Advanced Seminar on Safety and Function of Food, 修士課程, 農学院, 食品の安全、予測微生物学、食料確保と安全性、植物由来機能性食品、微生物由来機能性食品、腸内細菌叢の改変に基づいた機能性食品、食肉由来機能性食品
  • 2021, 大学院共通授業科目（一般科目）：自然科学・応用科学, Inter-Graduate School Classes(General Subject):Natural and Applied Sciences, 修士課程, 大学院共通科目, 食品安全性、予測微生物、食料確保と安全性、植物由来機能性食品、微生物由来機能性食品、腸内細菌叢の改変に基づいた機能性食品、食肉由来機能性食品
  • 2021, 環境と人間, Environment and People, 学士課程, 全学教育, 食のバリューチェーン、Society 5.0、エネルギー、異分野融合、持続可能性、フィールド、ロバストネス（強靱性）
  • 2021, 物理学概論, Introduction to Physics, 学士課程, 農学部, 力学，エネルギー，運動，波動，熱力学，電磁気学，光，量子力学，原子核，放射線
  • 2021, 一般教育演習(ﾌﾚｯｼｭﾏﾝｾﾐﾅｰ), Freshman Seminar, 学士課程, 全学教育, 食べ物，食卓，農畜産物，食品，品質，美味しさ，安全性
  • 2021, 農産物・食品加工工学Ⅰ, Agricultural and Food Process Engineering Ⅰ, 学士課程, 農学部, 食料生産，農畜産物，食品，加工と保蔵，品質，美味しさ，安全性，ポストハーベスト技術
  • 2021, 農産物・食品加工工学Ⅱ, Agricultural and Food Process Engineering Ⅱ, 学士課程, 農学部, 食料生産，農畜産物，食品，ポストハーベスト技術，食味評価，品質評価，鮮度保持，安全性，微生物制御，HACCP
  • 2021, 機械設計製図, Machinery Design and Drawing, 学士課程, 農学部, 機械，設計，要素，製図
  • 2021, 材料力学, Strength of Materials, 学士課程, 農学部, 内力，応力，ひずみ，力の釣合，弾性，はり，柱，モーメント
  • 2021, 材料力学演習, Seminar in Strength of Materials, 学士課程, 農学部, 内力，外力，応力，歪み，力のつりあい，弾性，はり，柱，ねじり，曲げ
  • 2021, 環境と人間, Environment and People, 学士課程, 全学教育, 土壌、水、大気、自然エネルギー、地域、物質循環、Information and communication technology (ICT) と農業生産、作物生産技術、持続的食料生産、農産物の収穫後技術と品質
  • 2021, 一般教育演習(ﾌﾚｯｼｭﾏﾝｾﾐﾅｰ), Freshman Seminar, 学士課程, 全学教育, 食料、安全、作物生産、放射能汚染、食品微生物、酵素利用技術、毒物、ガン、アレルギー、メタボリックシンドローム、腸内細菌叢、保健機能食品

researchmap

プロフィール情報

学位

  • 博士（農学）（北海道大学）

プロフィール情報

  • 姓

    小関, コセキ

  • 名

    成樹, シゲノブ

  • ID各種

    J-8317-2012, 201501029971041343

対象リソース

業績リスト

研究キーワード

  • 予測微生物学   数理モデル   予測モデル   殺菌   適合溶質   確率論   代謝阻害   アミノ酸   細菌   増殖阻害   食品品質   食品   

研究分野

  • ライフサイエンス / 食品科学 / 食品工学，食品安全

経歴

  • 2020年07月 - 現在 北海道大学 大学院農学研究院 教授
  • 2013年08月 - 2020年06月 北海道大学 (連合)農学研究科(研究院) 准教授
  • 2003年04月 - 2013年07月 農研機構 食品総合研究所
  • 2010年03月 - 2011年03月 タスマニア大学農学部 客員研究員
  • 1998年04月 - 1999年03月 三栄源エフ・エフ・アイ株式会社

委員歴

  • 2018年03月 - 現在   Joint FAO/WHO Expert Meeting on Microbiological Risk Assessment (JEMRA), Member
  • 2016年04月 - 現在   内閣府食品安全委員会   評価技術ワーキンググループ
  • 2013年10月 - 現在   内閣府食品安全委員会   微生物・ウィルス専門調査委員会

受賞

  • 2010年03月 第14回 安藤百福賞 発明発見奨励賞「食品における有害微生物の増殖および死滅の予測：数理モデルと情報技術の活用」
     
    受賞者: 小関 成樹

論文

  • Hiroki Abe, Akihiro Ando, Kento Koyama, Shigenobu Koseki
    Microbial Risk Analysis 27-28 100316 - 100316 2024年12月
  • Haruka Iino, Shuso Kawamura, Edenio Olivares Díaz, Hiroyuki Ishizu, Toru Nagata, Shigenobu Koseki
    Journal of Food Measurement and Characterization 2024年10月
  • Kiyoshi Kawai, Tomochika Sogabe, Hiroshi Nakagawa, Takeshi Yamada, Shigenobu Koseki
    Journal of Food Engineering 375 112066 - 112066 2024年08月
  • Kazuho Aonishi, Shungo Miyao, Lisa Yokoi, Naoki Kitaoka, Kento Koyama, Hideyuki Matsuura, Shigenobu Koseki
    Journal of agricultural and food chemistry 2024年07月04日 
    Maillard reaction products (MRPs) of xylose with phenylalanine and xylose with proline exhibit high antibacterial activity. However, the active antibacterial compounds in MRPs have not yet been identified or isolated. This study aimed to isolate the active compounds in the two antibacterial MRPs. The organic layer of the MRP solution was separated and purified using silica gel chromatography and high-performance liquid chromatography. The chemical structures of the isolated compounds were determined by mass spectrometry and nuclear magnetic resonance spectroscopy. The compounds inhibited the growth of Bacillus cereus and Salmonella Typhimurium at 25 °C for 7 days at a concentration of 0.25 mM. Furthermore, the isolated compounds inhibited the growth of naturally occurring microflora of lettuce and chicken thighs at 25 °C for 2 days at a concentration of 0.5-1.0 mM. The antibacterial compounds found in MRPs demonstrated a wide range of effectiveness and indicated their potential as alternative preservatives.
  • Hidemoto Yabe, Hiroki Abe, Yoshiki Muramatsu, Kento Koyama, Shige Koseki
    Applied and Environmental Microbiology 90 6 2024年06月18日 
    ABSTRACT Desiccation tolerance of pathogenic bacteria is one strategy for survival in harsh environments, which has been studied extensively. However, the subsequent survival behavior of desiccation-stressed bacterial pathogens has not been clarified in detail. Herein, we demonstrated that the effect of desiccation stress on the thermotolerance of Escherichia coli O157:H7 in ground beef was limited, and its thermotolerance did not increase. E. coli O157:H7 was inoculated into a ground beef hamburger after exposure to desiccation stress. We combined a bacterial inactivation model with a heat transfer model to predict the survival kinetics of desiccation-stressed E. coli O157:H7 in a hamburger. The survival models were developed using the Weibull model for two-dimensional pouched thin beef patties (ca. 1 mm), ignoring the temperature gradient in the sample, and a three-dimensional thick beef patty (ca. 10 mm), considering the temperature gradient in the sample. The two-dimensional (2-D) and three-dimensional (3-D) models were subjected to stochastic variations of the estimated Weibull parameters obtained from 1,000 replicated bootstrapping based on isothermal experimental observations as uncertainties. Furthermore, the 3-D model incorporated temperature gradients in the sample calculated using the finite element method. The accuracies of both models were validated via experimental observations under non-isothermal conditions using 100 predictive simulations. The root mean squared errors in the log survival ratio of the 2-D and 3-D models for 100 simulations were 0.25–0.53 and 0.32–2.08, respectively, regardless of the desiccation stress duration (24 or 72 h). The developed approach will be useful for setting appropriate process control measures and quantitatively assessing food safety levels. IMPORTANCE Acquisition of desiccation stress tolerance in bacterial pathogens might increase thermotolerance as well and increase the risk of foodborne illnesses. If a desiccation-stressed pathogen enters a kneaded food product via cross-contamination from a food-contact surface and/or utensils, proper estimation of the internal temperature changes in the kneaded food during thermal processing is indispensable for predicting the survival kinetics of desiccation-stressed bacterial cells. Various survival kinetics prediction models that consider the uncertainty or variability of pathogenic bacteria during thermal processing have been developed. Furthermore, heat transfer processes in solid food can be estimated using finite element method software. The present study demonstrated that combining a heat transfer model with a bacterial inactivation model can predict the survival kinetics of desiccation-stressed bacteria in a ground meat sample, corresponding to the temperature gradient in a solid sample during thermal processing. Combining both modeling procedures would enable the estimation of appropriate bacterial survival kinetics in solid food.
  • Sei Abe, Takahiro Matsui, Shige Koseki, Kento Koyama
    Food Quality and Preference 105167 - 105167 2024年03月
  • Raki Takemoto, Takashi Watanabe, Nobutaka Nakamura, Shige Koseki, Kento Koyama
    Journal of Food Measurement and Characterization 18 3 1776 - 1785 2023年12月20日
  • Edenio Olivares Díaz, Haruka Iino, Kento Koyama, Shuso Kawamura, Shigenobu Koseki, Suxing Lyu
    Food Chemistry 429 136907 - 136907 2023年12月
  • Hiroki Abe, Alberto Garre, Shige Koseki, Heidy M.W. den Besten, Marcel H. Zwietering
    Food Control 152 109831 - 109831 2023年10月
  • Takahiro Matsui, Hiroyuki Sugimori, Shige Koseki, Kento Koyama
    Postharvest Biology and Technology 203 2023年09月 
    Internal rot of avocado fruit (Persea americana), attributable to fungal infection, occurs at the end of the ripening process and causes only minor changes in the appearance and texture of the fruit surface. Manual inspection of rot by sight and touch commonly conducted in countries importing avocado fruit is time-consuming, labor-intensive, and subjective. In this context, X-ray line scanning has been proven as an advantageous method of fruit rot detection because of its speed of data acquisition and the indication of internal rot by bright regions in associated images. However, some fruit internal disorders exhibit only poor changes in contrast, resulting in low detectability by traditional image processing. This study aimed to test the effectiveness of a detection model using deep learning-based semantic segmentation in identifying two types of fruit rot, stem-end and body rot, in Hass avocados. Therefore, U-net+ + was trained and validated via 5-fold cross-validation to classify every pixel in an X-ray image as either infected or not. Then, each X-ray image was binarily classified based on either the presence or absence of internal fruit rots, achieving an accuracy of 0.98. Furthermore, the percentage of infected area was quantified with a root mean squared error (RMSE) of 3.15 %. Lastly, the proposed model detected both stem-end and body rot as well as rot along low-contrast fruit edges. The results of this study indicate that the proposed automatic inspection system using deep learning-based X-ray image analysis can effectively detect internal rot in Hass avocado fruit. This non-destructive, objective detection model can therefore increase efficiency and reduce misclassification in post-harvest avocado inspection. Furthermore, deep learning-based X-ray imaging has potential for applications in fruit inspection for internal cavities attributable to diseases or wounds.
  • Eisuke Maesaka, Satoshi Kukuminato, Kazuho Aonishi, Kento Koyama, Shigenobu Koseki
    Journal of Food Protection 100140 - 100140 2023年08月
  • Takashi Yamamoto, J. Nicholas Taylor, Shige Koseki, Kento Koyama
    LWT 114449 - 114449 2023年01月
  • Junpei Hosoe, Junya Sunagawa, Shinji Nakaoka, Shige Koseki, Kento Koyama
    Frontiers in Food Science and Technology 2 2022年12月15日 
    Although bacterial population behavior has been investigated in a variety of foods in the past 40 years, it is difficult to obtain desired information from the mere juxtaposition of experimental data. We predicted the changes in the number of bacteria and visualize the effects of pH, aw, and temperature using a data mining approach. Population growth and inactivation data on eight pathogenic and food spoilage bacteria under 5,025 environmental conditions were obtained from the ComBase database (www.combase.cc), including 15 food categories, and temperatures ranging from 0°C to 25°C. The eXtreme gradient boosting tree was used to predict population behavior. The root mean square error of the observed and predicted values was 1.23 log CFU/g. The data mining model extracted the growth inhibition for the investigated bacteria against aw, temperature, and pH using the SHapley Additive eXplanations value. A data mining approach provides information concerning bacterial population behavior and how food ecosystems affect bacterial growth and inactivation.
  • Raki Takemoto, Kento Koyama, Takashi Watanabe, Shige Koseki, Nobutaka Nakamura
    Food Packaging and Shelf Life 34 100965 - 100965 2022年12月
  • Jian Chen, Rendi Yang, Yongzheng Wang, Shigenobu Koseki, Linglin Fu, Yanbo Wang
    Food Microbiology 2022年12月
  • Takahiro Matsui, Tatsuki Kamata, Shige Koseki, Kento Koyama
    Postharvest Biology and Technology 192 111996 - 111996 2022年10月
  • Tomochika Sogabe, Hiroshi Nakagawa, Takeshi Yamada, Shigenobu Koseki, Kiyoshi Kawai
    Biophysical Journal 2022年09月
  • Y. Takahashi, H. Abe, K. Koyama, S. Koseki
    Letters in Applied Microbiology 75 2 388 - 395 2022年08月 
    Abstract To develop a mechanistic bacterial dose–response model, based on the concept of Key Events Dose–Response Framework (KEDRF), this study aimed to investigate the invasion of intestinal model cells (Caco-2) by Salmonella Typhimurium and Listeria monocytogenes and described the behaviour of both pathogens as a mathematical model using Bayesian inference. Monolayer-cultured Caco-2 cells (approximately 105 cells) were co-cultured with various concentrations (103–107 colony forming unit [CFU] ml−1) of Salm. Typhimurium and L. monocytogenes for up to 9 h to investigate the invasion of the pathogens into the Caco-2 cells. While an exposure of ≥103 CFU ml−1 of Salm. Typhimurium initiated the invasion of Caco-2 cells within 3 h, much less exposure (102 CFU ml−1) of L. monocytogenes was sufficient for invasion within the same period. Furthermore, while the maximum number of invading Salm. Typhimurium cells reached by approximately 103 CFU cm−2 for 6-h exposure, the invading maximum numbers of L. monocytogenes cells increased by approximately 106 CFU cm−2 for the same exposure period. The invasion kinetics of both the pathogens was successfully described as an asymptotic exponential mathematical model using Bayesian inference. The developed pathogen invasion model allowed the estimation of probability of Salm. Typhimurium and L. monocytogenes infection, based on the physiological natures of digestion process, which was comparable to the published dose–response relationship. The invasion models developed in the present study will play a key role in the development of an alternative pathogen dose–response model based on KEDRF concept.
  • Marin Tsujihashi, Saki Tanaka, Kento Koayama, Shigenobu Koseki
    Food and Bioprocess Technology 15 6 1343 - 1358 2022年06月
  • Kohei Takeoka, Hiroki Abe, Kento Koyama, Shigenobu Koseki
    Food Microbiology 102 103932 - 103932 2022年04月
  • Rio Okaniwa, Kento Koyama, Shigenobu Koseki
    Journal of Food Measurement and Characterization 16 1 12 - 18 2022年02月
  • Kento Koyama, Kyosuke Kubo, Satoko Hiura, Shige Koseki
    Journal of Microbiological Methods 192 106366 - 106366 2022年01月
  • Kyeongmin Lee, Kento Koyama, Kiyoshi Kawai, Shigenobu Koseki
    Microbiology Spectrum 9 3 2021年12月22日 
    The mechanical glass transition temperature ( T g ) of dried Cronobacter sakazakii cells varied depending on differences in drying methods and water activity (a w ) levels. Because the T g of the dried bacterial cells varied depending on the drying method and a w , the T g will play an important role as an operational factor in the optimization of dry food processing for controlling microbial contamination in the future.
  • Satoshi Kukuminato, Kento Koyama, Shigenobu Koseki
    Microbiology Spectrum 9 3 2021年12月22日 
    Although the antimicrobial effect of melanoidins has been reported in some foods, there have been few comprehensive investigations on the antimicrobial activity of combinations of reaction substrates of the Maillard reaction. The present study comprehensively investigated the potential of various combinations of reducing sugars and amino acids. Because the melanoidins examined in this study were produced simply by heating in an autoclave at 121°C for 60 min, the of the targeted melanoidins can be easily produced.
  • Satoko Hiura, Shige Koseki, Kento Koyama
    Scientific Reports 11 1 2021年12月 
    AbstractIn predictive microbiology, statistical models are employed to predict bacterial population behavior in food using environmental factors such as temperature, pH, and water activity. As the amount and complexity of data increase, handling all data with high-dimensional variables becomes a difficult task. We propose a data mining approach to predict bacterial behavior using a database of microbial responses to food environments. Listeria monocytogenes, which is one of pathogens, population growth and inactivation data under 1,007 environmental conditions, including five food categories (beef, culture medium, pork, seafood, and vegetables) and temperatures ranging from 0 to 25 °C, were obtained from the ComBase database (www.combase.cc). We used eXtreme gradient boosting tree, a machine learning algorithm, to predict bacterial population behavior from eight explanatory variables: ‘time’, ‘temperature’, ‘pH’, ‘water activity’, ‘initial cell counts’, ‘whether the viable count is initial cell number’, and two types of categories regarding food. The root mean square error of the observed and predicted values was approximately 1.0 log CFU regardless of food category, and this suggests the possibility of predicting viable bacterial counts in various foods. The data mining approach examined here will enable the prediction of bacterial population behavior in food by identifying hidden patterns within a large amount of data.
  • Shinya Doto, Hiroki Abe, Kento Koyama, Shigenobu Koseki
    Food Control 130 108288 - 108288 2021年12月 [査読有り]
  • Takashi Yamamoto, J. Nicholas Taylor, Shige Koseki, Kento Koyama
    Journal of Microbiological Methods 190 106326 - 106326 2021年11月
  • Byeong-Hyo Cho, Shigenobu Koseki
    Scientia Horticulturae 288 2021年10月15日 
    Banana quality and ripening stages were studied at four different temperatures (20, 25, 27.5, and 30 °C) using a smartphone camera and an artificial neural network (ANN). Changes in chemical and physical properties such as firmness, total soluble solids (TSS), pH, and ratio of pulp to peel, were determined and the relationship with color features (L*a*b*, hue, saturation, value [HSV], and luminance and chrominance [YUV]) were extracted from red, green, blue (RGB) images. ANN models based on color features were used to predict the quality indices of bananas during the ripening process. In addition, the developed models were verified by the coefficient of determination (R2), root mean squared error (RMSE), and the ratio of performance to deviation (RPD). The ANN model predicted the firmness and TSS of banana efficiently, with R2 values higher than 0.96 and RMSE values less than 72.32 and 1.40 for firmness and TSS, respectively. However, the ANN model was not suitable for predicting the pH value and ratio of pulp to peel with R2 values less than 0.60 and RMSE values of over 0.20 and 0.23 for pH and the ratio of pulp to peel, respectively. Thus, we demonstrated a post-harvest methodology to determine the ripening status of bananas by predicting their quality indices during the ripening process on a smartphone camera using ANN, and suggest smartphone camera as a potential tool to estimate product quality.
  • Yuto Fuchisawa, Hiroki Abe, Kento Koyama, Shigenobu Koseki
    Journal of Applied Microbiology 132 2 1467 - 1478 2021年09月23日
  • Kento Koyama, Satoko Hiura, Hiroki Abe, Shige Koseki
    Journal of Theoretical Biology 525 110758 - 110758 2021年09月
  • Yanbo Wang, Yongzheng Wang, Jian Chen, Shigenobu Koseki, Qing Yang, Hejun Yu, Linglin Fu
    LWT-FOOD SCIENCE AND TECHNOLOGY 149 111749 - 111749 2021年09月 
    Pseudomonas fluorescens and Shewanella baltica are specific spoilage organisms (SSOs) of most seafood products. Both of them can cell-to-cell communicate through quorum sensing (QS), facilitating the spoilage activities such as protease secretion, flagellar movement, and biofilm formation. Thus, it is important to screen the quorum sensing inhibitors (QSI) of P. fluorescens and S. baltica. In this study, we tried to apply a high-throughput virtual screening technology to select QSIs candidates. Three amino acid sequences from the key QS regulator-LuxR/I family (the LuxR and LuxI proteins of P. fluorescens, and the LuxR of S. baltica) were targeted and analyzed. Their 3D structures were subsequently constructed for the QSIs candidates' screen of both P. fluorescens and S. baltica. The candidates of cytidine-5'-monophosphate (5'-CMP) and 5'-adenylic acid (5'-AMP) with high scores exerted strong antagonistic effects against both P. fluorescens and S. baltica QS. The addition of 5'-CMP and 5'-AMP also inhibit QS-controlled phenotypes (swimming motility, protease activity, EPS, and biofilm formation) in P. fluorescens and S. baltica. Furthermore, the exogenous addition of 5'-CMP and 5'-AMP could retard the spoilage process of salmon slices during low-temperature storage by inhibiting the production of extracellular protease, siderophores, and Total Volatile Basic Nitrogen (TVB-N).
  • Hiroki Abe, Kohei Takeoka, Yuto Fuchisawa, Kento Koyama, Shigenobu Koseki
    Applied and Environmental Microbiology 87 20 2021年08月04日 
    Based on the mechanistic approach called the key events dose-response framework (KEDRF), an alternative to previous nonmechanistic approaches, the dose-response models for infection probability of C. jejuni were developed considering with age of people who ingest pathogen and food type. The developed predictive framework illustrates highly accurate prediction of dose (minimum difference 0.21 log CFU) for a certain infection probability compared with the previously reported dose-response relationship.
  • Kento Koyama, Jukka Ranta, Kohei Takeoka, Hiroki Abe, Shige Koseki, Andrew J. McBain
    Applied and Environmental Microbiology 87 15 2021年07月13日 
    Since microbial strains vary in their growth and activation patterns in food materials, it is important to accurately predict these patterns for quantitative microbial risk assessment. However, most previous studies in this area have used highly resistant strains, which could lead to inaccurate predictions.
  • Umi Ogawa, Kento Koyama, Shigenobu Koseki
    JOURNAL OF MICROBIOLOGICAL METHODS 186 2021年07月 
    The concept of dielectrophoresis (DEP), which involves the movement of neutral particles by induced polarization in nonuniform electric fields, has been exploited in various biological applications. However, only a few studies have investigated the use of DEP for detecting and enumerating microorganisms in foodstuffs. Therefore, we aimed to evaluate the accuracy and efficiency of a DEP-based method for enumerating viable bacteria in three raw foods: freshly cut lettuce, chicken breast, and minced pork. The DEP separation of bacterial cells was conducted at 20 V of output voltage and 6000 to 9000 kHZ of frequency with sample conductivity of 30-70 mu S/cm. The accuracy and validity of the DEP method for enumerating viable bacteria were compared with those of the conventional culture method; no significant variation was observed. We found a high correlation between the data obtained using DEP and the conventional aerobic plate count culture method, with a high coefficient of determination (R-2 > 0.90) regardless of the food product; the difference in cell count data between both methods was within 1.0 log CFU/mL. Moreover, we evaluated the efficiency of the DEP method for enumerating bacterial cells in chicken breasts subjected to either freezing or heat treatment. After thermal treatment at 55 degrees C and 60 degrees C, the viable cell counts determined via the DEP method were found to be lower than those obtained using the conventional culture method, which implies that the DEP method may not be suitable for the direct detection of injured cells. In addition to its high accuracy and efficiency, the DEP method enables the determination of viable cell counts within 30 min, compared to 48 h required for the conventional culture method. In conclusion, the DEP method may be a potential alternative tool for rapid determination of viable bacteria in a variety of foodstuffs.
  • Satoko Hiura, Hiroki Abe, Kento Koyama, Shige Koseki
    Frontiers in Microbiology 12 2021年06月24日 
    Conventional regression analysis using the least-squares method has been applied to describe bacterial behavior logarithmically. However, only the normal distribution is used as the error distribution in the least-squares method, and the variability and uncertainty related to bacterial behavior are not considered. In this paper, we propose Bayesian statistical modeling based on a generalized linear model (GLM) that considers variability and uncertainty while fitting the model to colony count data. We investigated the inactivation kinetic data of Bacillus simplex with an initial cell count of 105 and the growth kinetic data of Listeria monocytogenes with an initial cell count of 104. The residual of the GLM was described using a Poisson distribution for the initial cell number and inactivation process and using a negative binomial distribution for the cell number variation during growth. The model parameters could be obtained considering the uncertainty by Bayesian inference. The Bayesian GLM successfully described the results of over 50 replications of bacterial inactivation with average of initial cell numbers of 101, 102, and 103 and growth with average of initial cell numbers of 10–1, 100, and 101. The accuracy of the developed model revealed that more than 90% of the observed cell numbers except for growth with initial cell numbers of 101 were within the 95% prediction interval. In addition, parameter uncertainty could be expressed as an arbitrary probability distribution. The analysis procedures can be consistently applied to the simulation process through fitting. The Bayesian inference method based on the GLM clearly explains the variability and uncertainty in bacterial population behavior, which can serve as useful information for risk assessment related to food borne pathogens.
  • Shige Koseki, Kento Koyama, Hiroki Abe
    Current Opinion in Food Science 39 60 - 67 2021年06月
  • Kiyoshi Kawai, Kyoya Sato, Kyeongmin Lee, Shigenobu Koseki
    Journal of Food Science 2021年04月
  • Kento Koyama, Marin Tanaka, Byeong-Hyo Cho, Yusaku Yoshikawa, Shige Koseki
    PLOS ONE 16 3 e0248769 - e0248769 2021年03月19日 
    The visual perception of freshness is an important factor considered by consumers in the purchase of fruits and vegetables. However, panel testing when evaluating food products is time consuming and expensive. Herein, the ability of an image processing-based, nondestructive technique to classify spinach freshness was evaluated. Images of spinach leaves were taken using a smartphone camera after different storage periods. Twelve sensory panels ranked spinach freshness into one of four levels using these images. The rounded value of the average from all twelve panel evaluations was set as the true label. The spinach image was removed from the background, and then converted into a gray scale and CIE-Lab color space (L*a*b*) and Hue, Saturation and Value (HSV). The mean value, minimum value, and standard deviation of each component of color in spinach leaf were extracted as color features. Local features were extracted using the bag-of-words of key points from Oriented FAST (Features from Accelerated Segment Test) and Rotated BRIEF (Binary Robust Independent Elementary Features). The feature combinations selected from the spinach images were used to train machine learning models to recognize freshness levels. Correlation analysis between the extracted features and the sensory evaluation score showed a positive correlation (0.5 < r < 0.6) for four color features, and a negative correlation (‒0.6 < r < ‒0.5) for six clusters in the local features. The support vector machine classifier and artificial neural network algorithm successfully classified spinach samples with overall accuracy 70% in four-class, 77% in three-class and 84% in two-class, which was similar to that of the individual panel evaluations. Our findings indicate that a model using support vector machine classifiers and artificial neural networks has the potential to replace freshness evaluations currently performed by non-trained panels.
  • Patricia IWEKA, Shuso KAWAMURA, Tomohiro MITANI, Takashi KAWAGUCHI, Shigenobu KOSEKI
    Engineering in Agriculture, Environment and Food 14 1 30 - 36 2021年
  • Tsuruma, N., Doto, S., Ishida, W., Koyama, K., Koseki, S.
    Food Control 122 107756 - 107756 2021年
  • Cho, B.-H., Koyama, K., Koseki, S.
    Journal of Food Measurement and Characterization 15 2 2021 - 2030 2021年
  • Fia Noviyanti, Shigemasa Shimizu, Yukie Hosotani, Shigenobu Koseki, Yasuhiro Inatsu, Susumu Kawasaki
    FOODBORNE PATHOGENS AND DISEASE 17 11 693 - 700 2020年11月 [査読有り][通常論文]
     
    The aim of this study was to evaluate the application of real-time polymerase chain reaction (PCR)-based quantification as a rapid and accurate tool for the monitoring and prediction of Listeria monocytogenes growth in pasteurized milk under constant and fluctuating temperature conditions. The growth of L. monocytogenes was monitored under constant temperature conditions at 4 degrees C, 10 degrees C, 15 degrees C, 20 degrees C, and 35 degrees C. High correlation was obtained between the bacterial growth rate and incubation temperature, where the R-2 of the slope of the square root model was calculated to be 0.993 and 0.996 for real-time PCR and the conventional culture method, respectively. Moreover, the obtained maximum specific growth rate (mu(max)) data plots were correlated with 188 L. monocytogenes mu(max) data points from the existing model according to ComBase database, with an R-2 of 0.961 for real-time PCR and of 0.931 for the conventional culture method. The growth models were examined under three different patterns of fluctuating temperature conditions ranging from 2 degrees C to 30 degrees C. The prediction results fell within +/- 20% of the relative error zone, showing that real-time PCR quantification could be used for fast, sensitive, and specific bacterial growth monitoring with high-throughput results. Real-time PCR should be considered a promising option and powerful tool for the construction of a bacterial growth prediction model for safety risk analysis in the dairy industry.
  • Edenio Olivares Díaz, Shuso Kawamura, Miki Matsuo, Shigenobu Koseki
    Environmental Control in Biology 58 4 123 - 130 2020年10月01日 
    A combination of physical and chemical properties defines the rice quality. During grain filling, kernel location in the panicle and ambient air temperature influence its physicochemical properties thereby affecting the quality of rice. Here, we implemented principal component analysis (PCA) to reduce the dimensionality of 10 characteristics of 719 harvested rice samples, comprised of 10 varieties produced from 2010 to 2017 in regions of Hokkaido, Japan, into latent variables PC-1 and PC-2, which explained 69.7％ of the total variance. The model increased the interpretability of the relationship among physicochemical properties of brown rice and temperatures during grain filling in a visually intuitive manner. Results showed that high temperatures in August lowered the quality of samples produced in some regions in 2013 and 2016 by increasing the percentage of immature kernels and protein. Also, high temperatures in September increased the quality of samples produced in some regions in 2011 and 2012 by increasing the percentage of mature kernels and decreasing amylose and protein levels. Moreover, in 2015 and 2017, low temperatures in August and September increased amylose levels, which negatively affected rice quality attributes. This information could contribute to the production of high-quality and palatable rice demanded by Japanese consumers.
  • Non-destructive determination of bovine milk progesterone concentration during milking using near-infrared spectroscopy
    Patricia Iweka, Shuso Kawamura, Tomohiro Mitani, Shigenobu Koseki
    Agricultural Engineering International: CIGR Journal 22 3 171 - 178 2020年09月01日 
    In the current dairy industry, an intensive demand for estrus detection and early diagnosis of pregnancy has been increasing. Progesterone concentration in bovine milk is used as an important indicator of estrus detection and early pregnancy diagnosis. Current method for milk progesterone determination is destructive in nature. In contrast, near-infrared spectroscopy (NIRS) is a non-destructive analytical method that can be used for milk quality determination but there has been limited study on using NIRS for milk progesterone concentration during milking. Thus, the objective of this study was to develop an online real-time NIR spectroscopic sensing system for milk progesterone determination during milking by using a specific enzyme immunosorbent assay as a reference (chemical) method. Milk spectra with a wavelength range of 700 to 1050 nm and milk samples were collected every 20 s during milking from four lactating Holstein cows for 28 days using the NIR spectroscopic sensing system. Calibration models were developed using partial least squares analytical method and the precision and accuracy of the models was validated. Milk progesterone concentration for each milking was calculated by taking the progesterone concentration of the milk predicted values and milk yield obtained every 20 s, and was compared with the milk progesterone concentration chemical analysis value for one milking (bucket milk). The results obtained show that one milking time measurement accuracy of progesterone concentration was reasonably good. By installing the NIR spectroscopic sensing system developed in this study into a milking robot, it could predict milk progesterone concentration for one milking with almost the same accuracy as chemical analysis. Thus, recording this predicted value every milking and monitoring the continuous transition of the milk progesterone concentrations, it becomes possible to use it for the detection of estrus status and for the diagnosis of pregnancy of each cow.
  • Hiroki Abe, Kento Koyama, Kohei Takeoka, Shinya Doto, Shigenobu Koseki
    Frontiers in Microbiology 11 2020年05月19日 [査読有り][通常論文]
     
    © Copyright © 2020 Abe, Koyama, Takeoka, Doto and Koseki. The objective of this study was to separately describe the fitting uncertainty and the variability of individual cell in bacterial survival kinetics during isothermal and non-isothermal thermal processing. The model describing bacterial survival behavior and its uncertainties and variabilities during non-isothermal inactivation was developed from survival kinetic data for Bacillus simplex spores under fifteen isothermal conditions. The fitting uncertainties in the parameters used in the primary Weibull model was described by using the bootstrap method. The variability of individual cells in thermotolerance and the true randomness in the number of dead cells were described by using the Markov chain Monte Carlo (MCMC) method. A second-order Monte Carlo (2DMC) model was developed by combining both the uncertainties and variabilities. The 2DMC model was compared with reduction behavior under three non-isothermal profiles for model validation. The bacterial death estimations were validated using experimentally observed surviving bacterial count data. The fitting uncertainties in the primary Weibull model parameters, the individual thermotolerance heterogeneity, and the true randomness of inactivated spore counts were successfully described under all the iso-thermal conditions. Furthermore, the 2DMC model successfully described the variances in the surviving bacterial counts during thermal inactivation for all three non-isothermal profiles. As a template for risk-based process designs, the proposed 2DMC simulation approach, which considers both uncertainty and variability, can facilitate the selection of appropriate thermal processing conditions ensuring both food safety and quality.
  • Yan Bai, Aliyu Idris Muhammad, Yaqin Hu, Shigenobu Koseki, Xinyu Liao, Shiguo Chen, Xingqian Ye, Donghong Liu, Tian Ding
    Food Research International 131 109041 - 109041 2020年05月 [査読有り][通常論文]
     
    © 2020 Elsevier Ltd In recent years, plasma activated water has attracted more attention as a new disinfectant. The purpose of this study was to explore impact of variation of different treatment conditions on the inactivation kinetics of Bacillus cereus spores by PAW. All survival curves showed that the number of spores has decreased rapidly at first, followed by tailing results from the reduction inactivation rate. A linear and two nonlinear models (Weibull and Log-logistic model) were fitted to these data, and Log-logistic model fitted the inactivation of the B. cereus spores best. B. cereus spores in 106 CFU/mL was reduced by 1.62–2.96 log CFU/mL by PAW at 55 °C due to the reactive species generated in PAW. Elevated temperature, lower initial spore concentration, lower bovine serum albumin content, and smaller activation volume of PAW considerably enhanced PAW inactivation of B. cereus spores. These results provide an approach to evaluate the inactivation efficacy of different treatment conditions for PAW.
  • Mahmoud Elafify, Hazim O. Khalifa, Maha Al-Ashmawy, Mohammed Elsherbini, Amera Abd El Latif, Takashi Okanda, Tetsuya Matsumoto, Shige Koseki, Adel Abdelkhalek
    Journal of Environmental Science and Health - Part B Pesticides, Food Contaminants, and Agricultural Wastes 55 3 265 - 272 2020年03月03日 [査読有り][通常論文]
     
    © 2019, © 2019 Taylor & Francis Group, LLC. Food contaminated with Shiga toxin-producing Escherichia coli (STEC) represents a hazardous public health problem worldwide. Therefore, the present study was performed to elucidate the virulent and antimicrobial resistance characteristics of STEC isolated from milk and dairy products marketed in Egypt. A total of 125 samples (raw market milk, bulk tank milk, Kareish cheese, white soft cheese, and small scale-produced ice cream, 25 each) were collected for determination the prevalence and antimicrobial resistance profiling of STEC. Thirty-six STEC isolates were recovered from milk and dairy products. Serological analysis illustrated that three isolates were E. coli O157:H7 and 33 isolates belonged to different serotypes. Molecular examination indicated that all isolates harboured stx1 and/or stx2 genes, 14 isolates expressed eaeA gene and 3 isolates possessed rfbE gene. Antimicrobial resistance profiling of the isolates was both phenotypically and genetically examined. Interestingly, 31 out of 36 (86.11%) isolates were multidrug-resistant and harboured the extended-spectrum β-lactamase encoding genes, namely, blaCTX-M-15, blaSHV-12 and blaCTX-M-14. Moreover, 12 isolates (33.33%) harboured plasmid-mediated quinolone resistant gene, qnrS. The overall conclusion of the current investigation indicated insufficient hygienic measures adopted during milking, handling, and processing leading to development of pathogenic and multidrug-resistant STEC.
  • Abe, H., Koyama, K., Koseki, S.
    Applied and Environmental Microbiology 87 1 2020年 
    ABSTRACT Current approaches used for dose-response modeling of low-dose exposures of pathogens rely on assumptions and extrapolations. These models are important for quantitative microbial risk assessment of food. A mechanistic framework has been advocated as an alternative approach for evaluating dose-response relationships. The objectives of this study were to investigate the invasion behavior of Campylobacter jejuni, which could arise as a foodborne illness even if there are low counts of pathogens, into Caco-2 cells as a model of intestinal cells and to develop a mathematical model for invading cell counts to reveal a part of the infection dose-response mechanism. Monolayer-cultured Caco-2 cells and various concentrations of C. jejuni in culture were cocultured for up to 12 h. The numbers of C. jejuni bacteria invading Caco-2 cells were determined after coculture for different time periods. There appeared to be a maximum limit to the invading bacterial counts, which showed an asymptotic exponential increase. The invading bacterial counts were higher with higher exposure concentrations (maximum, 5.0 log CFU/cm2) than with lower exposure concentrations (minimum, 0.6 log CFU/cm2). In contrast, the ratio of invading bacteria (number of invading bacteria divided by the total number of bacteria exposed) showed a similar trend regardless of the exposure concentration. Invasion of C. jejuni into intestinal cells was successfully demonstrated and described by the developed differential equation model with Bayesian inference. The model accuracy showed that the 99% prediction band covered more than 97% of the observed values. These findings provide important information on mechanistic pathogen dose-response relationships and an alternative approach for dose-response modeling. IMPORTANCE One of the infection processes of C. jejuni, the invasion behavior of the bacteria in intestinal epithelial cells, was revealed, and a mathematical model for prediction of the cell-invading pathogen counts was developed for the purpose of providing part of a dose-response model for C. jejuni based on the infection mechanism. The developed predictive model showed a high accuracy of more than 97% and successfully described the C. jejuni invading counts. The bacterial invasion predictive model of this study will be essential for the development of a dose-response model for C. jejuni based on the infection mechanism.
  • Sakai, K., Lee, J.H., Kocharunchitt, C., Ross, T., Jenson, I., Koyama, K., Koseki, S.
    Food and Bioprocess Technology 13 12 2094 - 2103 2020年
  • Cho, B.-H., Koyama, K., Olivares Díaz, E., Koseki, S.
    Food and Bioprocess Technology 13 9 1579 - 1587 2020年
  • Liao, X., Ma, Y., Daliri, E.B.-M., Koseki, S., Wei, S., Liu, D., Ye, X., Chen, S., Ding, T.
    Trends in Food Science and Technology 95 97 - 106 2020年 [査読有り][通常論文]
     
    © 2019 Elsevier Ltd Background: The discovery and use of antibiotics have produced tremendous benefits for human society, however, with the large-scale use of antibiotics in medicine, animal husbandry and other fields, more and more antibiotic-resistant bacteria have emerged. Since diseases caused by such antibiotic-resistant bacteria could require more drastic measures to treat, the emergence of such resistant bacteria in food has attracted much concern. Scope and approach: In this review, we summarized the interplay between antibiotic resistance and food-associated stress tolerance, and the hypothesized molecular mechanisms for the cross protection in bacteria. Key findings and conclusions: In this review, we found that some common food-associated stresses, such as cold, acid, osmosis and sanitizers could provide cross protection for bacteria against antibiotics. In turn, antibiotic resistance could also render bacteria more tolerant to food-associated stresses. Meanwhile, novel nonthermal technologies may more likely result in little or no difference in bacterial antibiotic resistance, and this can be an advantage over traditional sterilization methods. Several molecular mechanisms for the cross protection between antibiotics and food-associated stresses have been discussed in this review. General stress response (e.g., sigma factors and two-component system), SOS response, mutations, and other mechanisms have been proposed as strategies for bacteria acquisition of cross protection.
  • Patricia Iweka, Shuso Kawamura, Tomohiro Mitani, Takashi Kawaguchi, Shigenobu Koseki
    Environmental Control in Biology 58 1 1 - 6 2020年 [査読有り][通常論文]
     
    © 2020 Biotron Institute. All rights reserved. In recent times, there has been an urgent requirement for a technique that can be used by dairy farmers to assess the quality of milk of an individual cow during milking. A near-infrared (NIR) spectroscopic sensing system was designed on an experimental basis for the online assessment of the three major milk constituents (fat, protein, and lactose), solids not fat (SNF), milk urea nitrogen (MUN), and somatic cell count (SCC). This system was used to obtain the NIR spectra of non-homogenized milk during milking over a wavelength range of 700 to 1,050 nm. Calibration models for predicting three major milk constituents, SNF, MUN and SCC of non-homogenized milk were developed, and the precision and accuracy of the models were validated. The coefficients of determination, standard errors of prediction, and bias values showed high levels of precision and accuracy for the prediction of the considered parameters. The results indicated that the developed NIR spectroscopic sensing system can be used to assess milk quality in real-time during milking. This system can provide dairy farmers with information concerning milk quality and physiological condition of each cow, and can therefore optimize dairy farm management.
  • Elafify, M., Chen, J., Abdelkhalek, A., Elsherbini, M., Al-Ashmawy, M., Koseki, S.
    Journal of Food Protection 83 4 644 - 650 2020年 [査読有り][通常論文]
     
    Copyright Ó, International Association for Food Protection D-Tryptophan (D-Trp) has a significant inhibitory effect on growth of gram-negative bacteria under osmotic stress. However, the inhibitory effect of D-Trp on the gram-positive Listeria monocytogenes under chilled and thermal stresses has not been evaluated previously. The effect of D-Trp on L. monocytogenes growth under cold and/or heat stress in milk and cream was dependent on the magnitude of the temperature stress. Low temperatures (4, 7, and 10°C) and treatment with 40 mM D-Trp resulted in significant inhibition of L. monocytogenes growth during the 4-week storage period. Lower temperatures more effectively inhibited growth. When added before thermal processing, 40 mM D-Trp completely inactivated L. monocytogenes (>6-log reduction) heated at 60°C for 25 min or 65°C for 20 min. These results suggest that D-Trp can be used as a preservative for controlling the growth of L. monocytogenes in milk and cream at refrigeration temperatures and could be used to enhance the thermal inactivation of L. monocytogenes.
  • Chen, J., Kawamura, S., Koseki, S.
    Food Control 110 107048 - 107048 2020年 [査読有り][通常論文]
     
    © 2019 Elsevier Ltd Current refrigeration temperatures are inadequate to restrain psychrophilic bacteria capable of survival and growth at low temperatures. Specifically, Listeria monocytogenes is strongly resistant to chilling stress and osmotic stress and tends to be more pathogenic during long-term refrigeration. Here, we demonstrated that D-tryptophan (D-Trp) reduced and delayed the psychrotrophic growth of L. monocytogenes at 4 °C in PYG medium during a 30-day period, and that >30 mM D-Trp further decreased the L. monocytogenes growth rate and extended the lag phase to a maximum of 400 h, which was 4-fold longer than that in the absence of D-Trp. In particular, 40 mM D-Trp alone significantly (P < 0.05) reduced L. monocytogenes growth by 3 log CFU/mL in concentration-dependent manner during a 30-day incubation at 4 °C, and 40 mM D-Trp combined with >3.0% NaCl resulted in an overall greater bacteriostatic effect accompanied by a partial bactericidal effect. Furthermore, 40 mM D-Trp significantly (P < 0.05) inhibited L. monocytogenes growth in artificially contaminated milk samples during extended refrigerated storage and maintained a low bacterial load (~103–104 CFU/mL) of L. monocytogenes throughout the 30-day refrigeration period. These results indicated that D-Trp significantly attenuated the psychrotrophic growth of L. monocytogenes at refrigerated temperatures, suggesting its potential efficacy as a food preservative.
  • Lee, K., Shoda, M., Kawai, K., Koseki, S.
    PLoS ONE 15 5 2020年 [査読有り][通常論文]
     
    © 2020 Public Library of Science. All rights reserved. Pathogenic bacteria such as Salmonella enterica exhibit high desiccation tolerance, enabling long-Term survival in low water activity (aw) environments. Although there are many reports on the effects of low aw on bacterial survival, the mechanism by which bacteria acquire desiccation tolerance and resistance to heat inactivation in low-Aw foods remains unclear. We focused on the glass transition phenomenon, as bacteria may acquire environmental tolerance by state change due to glass transition. In this study, we determined the glass transition temperature (Tg) in S. enterica serovars under different aw conditions using thermal rheological analysis (TRA). The softening behaviour associated with the state change of bacterial cells was confirmed by TRA, and Tg was determined from the softening behaviour. Tg increased as the aw decreased in all S. enterica serovars. For example, while the Tg of five S. enterica serovars was determined as 35.16°C to 57.46°C at 0.87 aw, the Tg of all the five serovars increased by 77.10°C to 83.30°C at 0.43 aw. Furthermore, to verify the thermal tolerance of bacterial cells, a thermal inactivation assay was conducted at 60°C for 10 min under each aw condition. A higher survival ratio was observed as aw decreased; this represented an increase in Tg for Salmonella strains. These results suggest that the glass transition phenomenon of bacterial cells would associate with environmental tolerance.
  • Hiura, S., Abe, H., Koyama, K., Koseki, S.
    Food Microbiology 91 103508 - 103508 2020年 [査読有り][通常論文]
     
    © 2020 Elsevier Ltd Kinetic models performing point estimation are effective in predicting the bacterial behavior. However, the large variation of bacterial behavior appearing in a small number of cells, i.e. equal or less than 102 cells, cannot be expressed by point estimation. We aimed to predict the variation of Escherichia coli O157:H7 behavior during inactivation in acidified tryptone soy broth (pH3.0) through Monte Carlo simulation and evaluated the accuracy of the developed model. Weibullian fitted parameters were estimated from the kinetic survival data of E. coli O157:H7 with an initial cell number of 105. A Monte Carlo simulation (100 replication) based on the obtained Weibullian parameters and the Poisson distribution of initial cell numbers successfully predicted the results of 50 replications of bacterial inactivation with initial cell numbers of 101, 102, and 103 cells. The accuracy of the simulation revealed that more than 83% of the observed survivors were within predicted range in all condition. 90% of the distribution in survivors with initial cells less than 100 is equivalent to a Poisson distribution. This calculation transforms the traditional microbial kinetic model into probabilistic model, which can handle bacteria number as discrete probability distribution. The probabilistic approach would utilize traditional kinetic model towards exposure assessment.
  • Mahmoud Elafify, Wageh Sobhy Darwish, Maha Al-Ashmawy, Mohammed Elsherbini, Shige Koseki, Shuso Kawamura, Adel Abdelkhalek
    Journal fur Verbraucherschutz und Lebensmittelsicherheit 14 4 399 - 407 2019年12月01日 [査読有り][通常論文]
     
    © 2019, Bundesamt für Verbraucherschutz und Lebensmittelsicherheit (BVL). The study aims to determine the prevalence and serotypes of Salmonella spp. in milk and dairy products sold on Egyptian markets, characterize their virulence-associated genes, and assess their antimicrobial profile. Furthermore, d-tryptophan was used as a new approach for controlling the growth of Salmonella in combination with heat stress. A total of 125 samples (raw market milk, bulk tank milk, Kareish cheese, white soft cheese, and small scale ice cream, 25 each) were used for assessing the prevalence of Salmonella spp. Nine Salmonella isolates with different serotypes were recovered from bulk tank milk (4/9; 44.44%) and Kariesh cheese (5/9; 55.55%), respectively. Antimicrobial susceptibility testing indicated that all isolates were resistant to streptomycin and erythromycin. PCR analysis revealed that 100%, 66.67% and 88.89% of the obtained isolates possessed invA, avrA and stn genes, respectively. d-Tryptophan (40 mM) in combination with heat stress had a significant inhibitory effect on Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium) added to control milk samples. The results indicate insufficient hygienic measures adopted during handling by dairies in Egypt. Therefore, strict hygienic approaches are recommended during milking, processing and distribution of dairy products in Egypt. A synergistic effect of d-tryptophan and heat stress is considered as a promising tool for controlling growth of Salmonella in milk.
  • Hiroki Abe, Kento Koyama, Shuso Kawamura, Shigenobu Koseki
    Food Microbiology 82 436 - 444 2019年09月 [査読有り][通常論文]
     
    © 2019 Elsevier Ltd The control of bacterial reduction is important to maintain food safety during thermal processing. The goal of this study was to illustrate and describe variability in bacterial population behavior during thermal processing as a probability distribution based on individual cell heterogeneity regarding heat resistance. Toward this end, we performed a Monte Carlo simulation via computer, and compared and validated the simulated estimations with observed values. Weibullian fitted parameters were estimated from the kinetic survival data of Bacillus simplex during thermal treatment at 94 °C. The variability in reductions of bacterial sporular populations was illustrated using Monte Carlo simulation based on the Weibull distribution of the parameters. In particular, variabilities in viable spore counts and survival probability of the B. simplex spore population were simulated in various replicates. We also experimentally determined the changes in survival probability and distributions of survival spore counts; notably, these were successfully predicted by the Monte Carlo simulation based on the kinetic parameters. The kinetic parameter-based Monte Carlo simulation could thus successfully illustrate bacterial population behavior variability during thermal processing as a probability distribution. The simulation approach may contribute to improving food quality through risk-based processing designs and enhance risk assessment model accuracy.
  • Sayuri Kuroda, Haruko Okuda, Wataru Ishida, Shigenobu Koseki
    Food Microbiology 78 38 - 45 2019年04月 [査読有り][通常論文]
     
    © 2018 Elsevier Ltd Growth/no growth boundary models for Bacillus spores that accounted for the effects of environmental pH, water activity (aw), acetic acid, lactic acid, bacterial strain, and storage period were developed using conventional logistic regression and machine learning algorithms. Growth in tryptic soy broth at 317 conditions comprising nine levels of pH (4.0–6.5), six levels of aw (0.85–1.00), six levels of acetic acid concentrations (0–0.8%), and five levels of lactic acid concentrations (0–0.8%) was examined to confirm growth limit conditions. All models developed using logistic regression, neural network, and deep learning on the basis of obtained datasets successfully described growth/no growth boundaries of three Bacillus species. Although the logistic regression model failed to describe growth limits under some conditions, neural network and deep learning approaches enabled to determine them in such cases. The developed models were evaluated by independent experimental data of growth in tryptic soy broth and in clam soup. The deep learning model enabled better prediction of independent data with smaller probabilistic variability values than those of the logistic regression and neural network models. The deep learning procedure can be utilized for growth boundary modeling to control bacterial growth safely and flexibly.
  • Edgar CAMBAZA, Shigenobu KOSEKİ, Shuso KAWAMURA
    International Journal of Agriculture Environment and Food Sciences 2019年03月14日
  • Cambaza, E., Koseki, S., Kawamura, S.
    Methods and Protocols 2 1 2019年03月 [査読有り][通常論文]
  • Koyama, K., Abe, H., Kawamura, S., Koseki, S.
    Journal of Theoretical Biology 469 172 - 179 2019年 [査読有り][通常論文]
     
    © 2019 Elsevier Ltd The traditional log-linear inactivation kinetics model considers microbial inactivation as a process that follows first-order kinetics. A basic concept of log reduction is decimal reduction time (D-value), which means time/dose required to kill 90% of the relevant microorganisms. D-value based on the first-order survival kinetics model is insufficient for reliable estimations of bacterial survivors following inactivation treatment. This is because the model does not consider the inactivation curvature and variability in bacterial inactivation. However, although the D-value has some limitations, it is widely used for risk assessment and sterilization time estimation. In this study, stochastic inactivation models are used in place of the conventional D-value to describe the probability of a population containing survivors. As representative bacterial inactivation normally follows a log-linear or log-Weibull model, we calculate the time required for a specific decrease in the number of cells and the number of survival cells as a probability distribution using the stochastic inactivation of individual cells in a population. We compare the probability of a population containing survivors calculated via the D-value, an inactivation kinetics model, and the stochastic formula. The stochastic calculation can be approximately estimated via a kinetic curvature model with less than 5% difference below the probability of a population containing survivors 0.1. This stochastic formula indicates that the D-value model would over- or under-estimate the probability of a population containing survivors when applied to inactivation kinetics with curvature. The results presented in this study show that stochastic analysis using mathematical models that account for variability in the individual cell inactivation time and initial cell number would lead to a realistic and probabilistic estimation of bacterial inactivation.
  • Jiao Li, Donghong Liu, Xiaojun Tian, Shigenobu Koseki, Shiguo Chen, Xingqian Ye, Tian Ding
    Critical reviews in food science and nutrition 59 sup1 S153 - S161 2019年 [査読無し][通常論文]
     
    Methicillin-resistant Staphylococcus aureus (MRSA) is a notorious bacterial pathogen that induces high mortality and morbidity. Due to the emergence of multiple resistance, antibiotic treatments are rapidly becoming ineffective for the related infections. Natural products, especially those derived from plants, have been proven to be effective agents with unique antibacterial properties through different mechanisms. This review interprets the resistance mechanisms of MRSA with the aim to conquer public health threat. Further, recent researches about plant antimicrobials that showed remarkable antibacterial activity against MRSA are recorded, including the crude plant extracts and purified plant-derived bioactive compounds. Novel anti-MRSA modalities of plant antimicrobials such as alteration in efflux pump, inhibition of pyruvate kinase, and disturbance of quorum sensing in MRSA are also summarized which may be promising alternatives to antibacterial drug development in future.
  • Edgar Cambaza, Shigenobu Koseki, Shuso Kawamura
    Foods 8 1 2019年 [査読有り][通常論文]
     
    © 2018 by the authors. Licensee MDPI, Basel, Switzerland. Deoxynivalenol (DON) is a well-known mycotoxin, responsible for outbreaks of gastrointestinal disorders in Japan. Fusarium graminearum, a parasite of cereal crops, produces this toxin and this is one of the reasons why it is important to understand its metabolism. It is possible to predict the mold's color change and the quantity of DON synthesized throughout its lifecycle. Furthermore, a w has been found to affect the amount of DON. This study aimed to analyze the potential of F. graminearum surface color as a predictor of DON concentration at a w = 0.94, 0.97, and 0.99. Thus, 36 specimens were incubated at 25 ◦ C, 12 at each a w . After 4, 8, 12, and 16 days, three specimens from each a w were collected for color analysis and DON quantification. For color analysis, photos were taken and red, green and blue (RGB) channels were measured on ImageJ software. DON was quantified through liquid chromatography (HPLC). Color changes were only observed at a w = 0.99 because at lower a w the molds presented high growth of white mycelium. Yet, DON increased in all cases. It was only possible to relate the colors with DON concentration at a w = 0.99, where they presented inverse proportionality.
  • Olivares Díaz, E., Kawamura, S., Matsuo, M., Kato, M., Koseki, S.
    Food Chemistry 286 297 - 306 2019年 [査読有り][通常論文]
     
    © 2019 Elsevier Ltd Amylose content is an important determinant of rice quality. Accurate non-destructive determination of amylose content remains a primary challenge for the rice industry. Here, we analysed the accuracy of three models for the non-destructive determination of amylose content. The models were developed by combining near-infrared spectra, colour, and physicochemical information relative to 832 brown rice samples from ten varieties produced between 2009 and 2017 in various regions of Hokkaido, Japan. Models describing low and ordinary amylose varieties were developed individually, merged, and validated using production year samples (2016–2017) different from the calibration set (2009–2015). The resulting accuracy was suitable for industrial application. With standard error of prediction = 0.70% and ratio of performance deviation = 3.56, the combination of near-infrared spectra and physicochemical information produced the most robust model, enabling more precise rice quality screening at grain elevators.
  • Olivares Díaz, E., Kawamura, S., Koseki, S.
    Biosystems Engineering 183 160 - 169 2019年 [査読有り][通常論文]
     
    © 2019 IAgrE The rice industry requires new technologies to increase production in response to world population growth. These include technologies that ensure rice quality in postharvest processing. Protein content defines rice quality and palatability. Differences in kernel thickness and maturity affect the protein level of harvested rice. We therefore analysed the relationship between kernel thickness and maturity on protein content of Japonica brown rice collected during postharvest processing. We fractionated the rice into six thickness fractions and classified each fraction into mature, immature and chalky levels of maturity. Results showed that thickness fraction and maturity level affected protein content. Each increase in thickness produced an increase in the percentage of sound whole kernel and a decrease in protein content. The mature sample had the lowest protein content among maturity levels within each thickness fraction. Based on sound whole kernel and protein content values, we classified the mature sample in higher thickness fractions as having high-quality appearance and palatability. There were significant differences in protein content between different thickness fractions of the mature sample suggested that we can sort rice protein by thickness fraction. Moreover, differences in protein content suggested that we can use the thickness grader and colour sorter machines to sort rice into high or low protein content fractions. This information can contribute to more accurate quality constituent determination through the development of a rice protein sorter. This would support the production of high-quality rice and help address the demand for more efficient technology for rice postharvest processing.
  • Koyama, K., Aspridou, Z., Koseki, S., Koutsoumanis, K.
    Frontiers in Microbiology 10 SEP 2019年 [査読有り][通常論文]
     
    © 2019 Koyama, Aspridou, Koseki and Koutsoumanis. Uncertainty analysis is the process of identifying limitations in scientific knowledge and evaluating their implications for scientific conclusions. In the context of microbial risk assessment, the uncertainty in the predicted microbial behavior can be an important component of the overall uncertainty. Conventional deterministic modeling approaches which provide point estimates of the pathogen’s levels cannot quantify the uncertainty around the predictions. The objective of this study was to use Bayesian statistical modeling for describing uncertainty in predicted microbial thermal inactivation of Salmonella enterica Typhimurium DT104. A set of thermal inactivation data in broth with water activity adjusted to 0.75 at 9 different temperature conditions obtained from the ComBase database (www.combase.cc) was used. A log-linear microbial inactivation was used as a primary model while for secondary modeling, a linear relation between the logarithm of inactivation rate and temperature was assumed. For comparison, data were fitted with a two-step and a global Bayesian regression. Posterior distributions of model’s parameters were used to predict Salmonella thermal inactivation. The combination of the joint posterior distributions of model’s parameters allowed the prediction of cell density over time, total reduction time and inactivation rate as probability distributions at different time and temperature conditions. For example, for the time required to eliminate a Salmonella population of about 107 CFU/ml at 65◦ C, the model predicted a time distribution with a median of 0.40 min and 5th and 95th percentiles of 0.24 and 0.60 min, respectively. The validation of the model showed that it can describe successfully uncertainty in predicted thermal inactivation with most observed data being within the 95% prediction intervals of the model. The global regression approach resulted in less uncertain predictions compared to the two-step regression. The developed model could be used to quantify uncertainty in thermal inactivation in risk-based processing design as well as in risk assessment studies.
  • Olivares Díaz, E., Kawamura, S., Kato, M., Nagata, T., Koseki, S.
    Journal of Cereal Science 90 2019年 [査読有り][通常論文]
     
    © 2019 Elsevier Ltd Amylose content contributes to the texture and the eating quality of rice. Industrial non-destructive measurement of the amylose content in rice using a near-infrared (NIR) spectrometer remains inaccurate. In this study, we analyzed whether using an NIR spectrometer along with a visible light (VIS) grain segregator improved the accuracy of conventional model for non-destructive determination of rice amylose content. NIR spectra collected from the NIR spectrometer and physical properties were collected from the VIS grain segregator from 603 milled samples of 10 varieties of rice produced between 2010 and 2016 in various regions of Hokkaido, Japan. Data were analyzed by partial least squares regression (PLS) and multiple linear regression (MLR) to develop a dual-step model. Our dual-step model was validated using production year samples (2016) that were different from the calibration set (2010–2015). Our method improved accuracy compared to the conventional method developed using data from an NIR spectrometer, with a standard error of prediction (SEP) = 0.94% and ratio of performance deviation (RPD) = 2.46. Our dual-step model also had the highest robustness when increasing the production year samples of the calibration set, enabling a more precise, accurate, and efficient rice quality screening in Japanese industry.
  • Koyama, K., Abe, H., Kawamura, S., Koseki, S.
    International Journal of Food Microbiology 290 125 - 131 2019年 [査読有り][通常論文]
     
    © 2018 Elsevier B.V. Decimal reduction time (D-value) based on the first-order survival kinetics model is not sufficient for reliable estimation of the bacterial survivors of inactivation treatment because the model does not consider inactivation curvature. However, even though doubt exists in the calculation of D-value, it is still widely used for risk assessment and sterilisation time estimation. This paper proposes an approach for estimating the time-to-inactivation and death probability of bacterial population that considers individual cell heterogeneity and initial number of cells via computer simulation. In the proposed approach, Weibull and Poisson distributions are respectively used to provide individual cell inactivation time variability and initial number of cells variability. Our simulation results show that the time-to-inactivation significantly depends on kinetics curvature and initial number of cells. For example, with increases in the initial number of cells, the respective variance of the time-to-inactivation of log-linear, concave downward curve, and concave upward curve remains constant, decreases, and increases, respectively. The death probability contour plot was successfully generated via our computer simulation approach without using D-value estimation. Further, the death probability calculated using our stochastic approach was virtually the same as that obtained using inactivation kinetics. We validated the simulation by using literature data for acid inactivation of Salmonella population. The results of this study indicate that inactivation curvature can replace D-value extrapolation to estimate the death probability of bacterial population. Further, our computer simulation facilitates realistic estimation of the time-to-inactivation of bacterial population. The R code used for the above stochastic calculation is outlined.
  • Jung-Hyun Lee, Akane Morita, Manabu Kuroshima, Shuso Kawamura, Shigenobu Koseki
    Journal of Food Measurement and Characterization 12 4 2899 - 2904 2018年12月16日 [査読有り][通常論文]
  • Abe Hiroki, Koyama Kento, Kawamura Shuso, Koseki Shigenobu
    INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY 285 129 - 135 2018年11月20日 [査読有り][通常論文]
     
    Stochastic models take into account the uncertainty and variability of predictions in quantitative microbial risk assessment. However, a model that considers thermal inactivation conditions can better predict whether or not bacteria in food are alive. To this end, we describe a novel probabilistic modelling procedure for accurately predicting thermal end point, in contrast to conventional kinetic models that are based on extrapolation of the D value. We used this new model to investigate changes in the survival probability of Salmonella enterica serotype Oranienburg during thermal processing. These changes were accurately described by a cumulative gamma distribution. The predicted total bacterial reduction time with a survival probability of 10-6-the commercial standard for sterility-was significantly shorter than that predicted by the conventional deterministic kinetic model. Thus, the survival probability distribution can explain the heterogeneity in total reduction time for a bacterial population. Furthermore, whereas kinetic methodologies may overestimate the time required for inactivation, our method for determining survival probability distribution can provide an accurate estimate of thermal inactivation and is therefore an important tool for quantitative microbial risk assessment of foods.
  • Cambaza, E.M., Koseki, S., Kawamura, S.
    Food Research 2 5 443 - 446 2018年10月 [査読有り][通常論文]
     
    © 2018 The Authors. Deoxynivalenol (DON) is a mycotoxin produced by Fusarium species, causing involuntary regurgitation in animals including humans. Some studies showed that its synthesis is influenced by environmental factors such as temperature and water activity (aw). This article presents a meta-analysis of two major studies on the phenomenon, discussing on what should be expected in future research in this direction. The specimens were cultured in maize and wheat. In all experiments, Fusarium graminearum was incubated at 15oC, 22oC, 25oC, 28oC and 30oC. At room temperature, the water activity was set to 0.95, 0.97, 0.99, and 0.995. Then, levels of DON were quantified weekly since the 14th day until the 49th day, using HPLC with UV detector at 220 nm. Temperature and water activity seem to have an impact on DON synthesis, though the true correlations still require further analysis.
  • Jian Chen, Hiroko Kudo, Kaito Kan, Shuso Kawamura, Shige Koseki
    Applied and Environmental Microbiology 84 19 2018年10月 [査読有り][通常論文]
  • Yukie Hosotani, Fia Noviyanti, Shigenobu Koseki, Yasuhiro Inatsu, Susumu Kawasaki
    LWT 96 426 - 431 2018年10月01日 [査読有り][通常論文]
     
    The aim of this study was to develop an estimation method for bacterial injury levels of Escherichia coli O157:H7 in food products. Bacterial growth was monitored in recovery medium and quantified by real-time PCR to quantify the growth delay phenomenon as growth delay time (GDT). The relationship between GDT and stress levels (salt-concentration: 9, 13, 15, and 17% stress exposure times:0, 6, 12, 18, and 24 h) was determined. The GDT increased with stress exposure time, and the higher the salt concentration was, the faster the GDT increased. Moreover, bacterial injury levels in 15% NaCl-containing media were estimated by a conventional culture-based method, bacterial membrane destruction assay, NADPH content assay, and intercellular ATP content assay. In these estimations, the result suggested a decrease in bacterial activity and increase in bacterial membrane destruction from 6 to 12 h of exposure, which was consistent with the results of the GDT monitoring method. Furthermore, the estimation of bacterial injury levels in high-salt food (fermented soybean paste) was investigated, and GDT extension was successfully observed until the bacteria completely reached sublethal conditions. Therefore, GDT monitoring by real-time PCR showed the ability to estimate bacterial injury levels along with other existing methods.
  • Cambaza, E., Koseki, S., Kawamura, S.
    International Journal of Environmental Research and Public Health 15 8 2018年08月 [査読有り][通常論文]
  • Cambaza, E., Koseki, S., Kawamura, S.
    Foods 7 7 2018年07月 [査読有り][通常論文]
  • Cambaza, E., Koseki, S., Kawamura, S.
    Agriculture (Switzerland) 8 7 2018年07月 [査読有り][通常論文]
  • Noviyanti, F., Hosotani, Y., Koseki, S., Inatsu, Y., Kawasaki, S.
    Foodborne Pathogens and Disease 15 7 406 - 412 2018年07月 [査読有り][通常論文]
  • Cambaza, E., Koseki, S., Kawamura, S.
    Agriculture (Switzerland) 8 7 2018年07月 [査読有り][通常論文]
  • Taiki Yoshida, Yuji Tasaka, Hyun Jin Park, Yuichi Murai, Hiroki Teramura, Shigenobu Koseki
    Journal of Visualization 21 2 253 - 265 2018年04月01日 [査読有り][通常論文]
     
    Abstract: We proposed a novel ultrasonic Doppler–echo visualization method that is expected to realize nondestructive visualization using an ultrasonic velocity profiler. The visualization uses information of both the Doppler velocity and echo intensity that have usually been used by the ultrasonic velocity profiler to obtain instantaneous velocity profiles. The feasibility of the method is confirmed by measurements of a rubber ball, apple, and tomato having different acoustic impedances, pulp hardnesses, shapes, and inner structures. Mathematical relations and image processing parameters were discussed to obtain images of the inner structures of test objects using the ultrasonic velocity profiler. Trial measurements of test objects elucidated that the Doppler velocity and echo intensity detect different features of the test objects. Using the Doppler velocity and echo intensity, the outlines and inner structures of the objects can be visualized.
  • Susumu Kawasaki, Yukie Hosotani, Fia Noviyanti, Shigenobu Koseki, Yasuhiro Inatsu
    LWT - Food Science and Technology 90 499 - 504 2018年04月01日 [査読有り][通常論文]
     
    We aimed to estimate the bacterial injury level from ground beef samples that underwent various heat exposure treatments. The growth delay time (GDT) in recovery medium was estimated by real-time PCR monitoring assay. Samples of Salmonella Enteritidis in PBS and ground beef were exposed to heat stress in water bath at 52.5–62.5 °C for 0–60 min. Heat-treated samples were transferred to fresh trypticase soy broth, and S. Enteritidis growth recovery was monitored by real-time PCR. Sampling was conducted every 2 h, and total DNA was extracted. The S. Enteritidis cell number was estimated by real-time PCR, and growth recovery curve was constructed from the DNA copy number of the Salmonella invA gene. Growth recovery curve was used for kinetic analysis of GDT. Injured bacteria level in ground beef samples after heat exposure shown differences compared to PBS, where ground beef samples had lower variations in GDT than did PBS samples. Relationship between GDT and heat exposure time was observed where the slope of GDT increased as heat exposure time extended. Recovery of heat-treated S. Enteritidis in near sub-lethal conditions in PBS and ground beef samples, which could not be evaluated by traditional culture methods, was successfully monitored by real-time PCR.
  • Taiki Yoshida, Yuji Tasaka, Hyun Jin Park, Yuichi Murai, Hiroki Teramura, Shigenobu Koseki
    Journal of Visualization 21 2 253 - 265 2018年04月01日 [査読有り][通常論文]
     
    Abstract: We proposed a novel ultrasonic Doppler–echo visualization method that is expected to realize nondestructive visualization using an ultrasonic velocity profiler. The visualization uses information of both the Doppler velocity and echo intensity that have usually been used by the ultrasonic velocity profiler to obtain instantaneous velocity profiles. The feasibility of the method is confirmed by measurements of a rubber ball, apple, and tomato having different acoustic impedances, pulp hardnesses, shapes, and inner structures. Mathematical relations and image processing parameters were discussed to obtain images of the inner structures of test objects using the ultrasonic velocity profiler. Trial measurements of test objects elucidated that the Doppler velocity and echo intensity detect different features of the test objects. Using the Doppler velocity and echo intensity, the outlines and inner structures of the objects can be visualized.
  • Lee, J.-H., Kawamura, S., Koseki, S.
    Food Science and Technology Research 24 2 283 - 287 2018年03月 [査読有り][通常論文]
  • Jung Hyun Lee, Rikako Harada, Shuso Kawamura, Shigenobu Koseki
    Food and Bioprocess Technology 11 1 185 - 193 2018年01月01日 [査読有り][通常論文]
     
    There is a lack of easy-to-use hardware providing clear indications regarding both current temperature and temperature history during thermal processing. The objective of this study was to use the Maillard reaction to develop a novel time-temperature integrator/indicator (TTI) that would be able to perform these tasks during the cooking process. To this end, we comprehensively tested the Maillard reaction using various conditions to determine those under which the reaction illustrated obvious color change when temperature was held at 75 °C for 1 min, which is the recommendation of the Japanese government regarding safe meat product cooking. After adjusting various parameters related to the reaction, we managed to deduce a reaction system of d-ribose (7.0 mol/kg) and l-lysine (3.0 mol/kg) with dibasic potassium phosphate (0.5 mol/kg) satisfying the color-change criterion. The developed Maillard reaction-based TTI consisted of two transparent plastic poaches connected through a loose half-seal. Breaking the half-seal by pushing with fingers results in the mixing of the solutions and the initiation of the Maillard reaction. The TTI was tested in hamburger cooking and its color clearly changed from colorless to brown in hamburger during the 1-min hold at 75 °C, and also successfully eliminated viable 106 CFU/g Escherichia coli O157:H7 cells. The developed TTI will enable to help ensure microbiological safety.
  • Kaito Kan, Jian Chen, Shuso Kawamura, Shigenobu Koseki
    Journal of Food Protection 81 1 25 - 30 2018年01月01日 [査読有り][通常論文]
     
    We previously reported that D-tryptophan exhibits adverse effects on bacterial physiology under osmotic stress. However, the mechanism by which D-tryptophan acts as an inhibitor and/or incompatible solute for bacterial growth has not yet been investigated in detail. In this study, we aimed to determine how osmotic pressure and temperature affect the antimicrobial effect of D-tryptophan. Even at the same level of osmotic pressure, D-tryptophan in conjunction with sodium chloride (NaCl) had a stronger inhibitory effect on the growth of Escherichia coli than that obtained by incubation with potassium chloride (KCl) and sucrose. Because D-tryptophan with NaCl showed the strongest inhibitory effect, we determined the optimum concentration combination of D-tryptophan and NaCl. The growth inhibition boundary conditions as a function of D-tryptophan and NaCl concentrations were determined by a logistic regression model. We found that the minimum level of NaCl for E. coli growth inhibition was 2.5% (w/v) together with 40 mM D-tryptophan. Moreover, the higher the NaCl concentration, the lower the concentration of D-tryptophan that was needed to inhibit bacterial growth. The logistic regression model that we developed enabled us to predict the concentrations required to inhibit bacterial growth. Furthermore, we examined the effect of incubation temperatures ranging from 15 to 468C on the antimicrobial effect of D-tryptophan. The higher the reaction temperature, the more rapid the decrease of viable E. coli that was observed. This trend is likely attributable to activation of physiological metabolism under the optimum growth temperature. Together, our findings should make a significant contribution to the development of a novel bacterial growth control strategy using D-tryptophan.
  • Diaz, E.O., Kawamura, S., Koseki, S.
    AMA, Agricultural Mechanization in Asia, Africa and Latin America 49 2 68 - 73 2018年 [査読有り][通常論文]
  • Non-destructive online real-time milk quality determination in a milking robot using near-infrared spectroscopic sensing system
    Patricia Iweka, Shuso Kawamura, Tomohiro Mitani, Shigenobu Koseki
    Arid Zone Journal of Engineering, Technology and Environment 18 121 - 128 2018年 [査読有り][通常論文]
  • Kento Koyama, Hidekazu Hokunan, Mayumi Hasegawa, Shuso Kawamura, Shigenobu Koseki
    FOOD MICROBIOLOGY 68 121 - 128 2017年12月 [査読有り][通常論文]
     
    Despite the development of numerous predictive microbial inactivation models, a model focusing on the variability in time to inactivation for a bacterial population has not been developed. Additionally, an appropriate estimation of the risk of there being any remaining bacterial survivors in foods after the application of an inactivation treatment has not yet been established. Here, Gamma distribution, as a representative probability distribution, was used to estimate the variability in time to inactivation for a bacterial population. Salmonella enterica serotype Typhimurium was evaluated for survival in a low relative humidity environment. We prepared bacterial cells with an initial concentration that was adjusted to 2 x 10n colony-forming units/2 mu l (n = 1, 2, 3, 4, 5) by performing a serial 10-fold dilution, and then we placed 2 ml of the inocula into each well of 96-well microplates. The microplates were stored in a desiccated environment at 10-20% relative humidity at 5, 15, or 25 degrees C. The survival or death of bacterial cells for each well in the 96-well microplate was confirmed by adding tryptic soy broth as an enrichment culture. The changes in the death probability of the 96 replicated bacterial populations were described as a cumulative Gamma distribution. The variability in time to inactivation was described by transforming the cumulative Gamma distribution into a Gamma distribution. We further examined the bacterial inactivation on almond kernels and radish sprout seeds. Additionally, we described certainty levels of bacterial inactivation that ensure the death probability of a bacterial population at six decimal reduction levels, ranging from 90 to 99.9999%. Consequently, the probability model developed in the present study enables us to estimate the death probability of bacterial populations in a desiccated environment over time. This probability model may be useful for risk assessment to estimate the amount of remaining bacteria in a given sample. (C) 2017 Elsevier Ltd. All rights reserved.
  • Suguru Murashita, Shuso Kawamura, Shigenobu Koseki
    JOURNAL OF FOOD PROTECTION 80 7 1198 - 1203 2017年07月 [査読有り][通常論文]
     
    Ice, widely used in the food industry, is a potential cause of food poisoning resulting from microbial contamination Direct microbial inactivation of ice is necessary because microorganisms may have been present in the source water used to make it and/or may have been introduced due to poor hygiene during production or handling of the ice. Nonthermal and nondestructive microbial inactivation technologies are needed to control microorganisms in ice. We evaluated the applicability of a UVC light emitting diode (UVC-LED) for microbial inactivation in ice. The effects of UV intensity and UV dose of the UVC-LED on Escherichia coli ATCC 25922 and a comparison of UVC-LED with a conventional UV lamp for effective bacterial inactivation in distilled water and ice cubes were investigated to evaluate the performance of the UVC-LED. Finally, we assessed the effects of the UVC-LED on pathogens such as E coli O157:H7, Salmonella Typhimurium, and Listeria monocyto genes in ice cubes. The results indicated that UVC-LED effectiveness depended on the UV dose at all UV intensity conditions (0.084, 0.025, 0.013, 0.007, and 0.005 mW/cm(2)) in ice and that UVC-LED could more efficiently inactivate E. coli ATCC 25922 in distilled water and ice than the UV lamp. At a UV dose of 2.64 mJ/cm(2), E. coli in distilled water was decreased by 0.90 log CFU/mL (UV lamp) and by more than 7.0 log CFU/mL (UVC-LED). At 15.2 mJ/cm(2), E. coli in ice was decreased by 3.18 log CFU/mL (UV lamp) and by 4.45 CFU/mL (UVC-LED). Furthermore, UVC-LED irradiation reduced the viable number of pathogens by 6 to 7 log cycles at 160 mJ/cm(2), although the bactericidal effect was somewhat dependent on the type of bacteria. L. monocyto genes in ice was relatively more sensitive to UVC irradiation than were E. coli O157:117 and Salmonella Typhimurium. These results demonstrate that UVC-LED irradiation could contribute to the safety of ice in the food industry.
  • Jun Wang, Shige Koseki, Mi-Ja Chung, Deog-Hwan Oh
    FRONTIERS IN MICROBIOLOGY 8 2017年06月 [査読有り][通常論文]
     
    This study aimed to investigate the growth kinetics of Staphylococcus aureus on rice cake and to determine the shelf life based on the probability model of the increase in S. aureus contamination on rice cake. Secondary models were developed based on the growth parameters derived from the Baranyi model at constant temperatures (15, 25, 35, and 45 0). External validation was then conducted using additional data under experimental conditions not used in development of the models to verify the performance and reliability of the developed model through different goodness-of-fit indices. Furthermore, the growth of S. aureus on rice cake under dynamic temperature was obtained with the root mean square error (RMSE) of 0.218 and the 90.9% acceptable prediction rate. In addition, probability models of the 1-, 2-, 3-, and 4-log increases of S. aureus on rice cake were also developed from the data, which could provide the probability and the time to a certain log increase. The results of validation demonstrated that the developed predictive model and the obtained growth parameters could be used for evaluating the growth behavior of S. aureus on rice cake under different conditions, and qualified to supply sufficient information for microbiological risk assessment studies of S. aureus on rice cake in Korea.
  • Jun Wang, Shige Koseki, Mi-Ja Chung, Deog-Hwan Oh
    FRONTIERS IN MICROBIOLOGY 8 2017年06月 [査読有り][通常論文]
     
    This study aimed to investigate the growth kinetics of Staphylococcus aureus on rice cake and to determine the shelf life based on the probability model of the increase in S. aureus contamination on rice cake. Secondary models were developed based on the growth parameters derived from the Baranyi model at constant temperatures (15, 25, 35, and 45 0). External validation was then conducted using additional data under experimental conditions not used in development of the models to verify the performance and reliability of the developed model through different goodness-of-fit indices. Furthermore, the growth of S. aureus on rice cake under dynamic temperature was obtained with the root mean square error (RMSE) of 0.218 and the 90.9% acceptable prediction rate. In addition, probability models of the 1-, 2-, 3-, and 4-log increases of S. aureus on rice cake were also developed from the data, which could provide the probability and the time to a certain log increase. The results of validation demonstrated that the developed predictive model and the obtained growth parameters could be used for evaluating the growth behavior of S. aureus on rice cake under different conditions, and qualified to supply sufficient information for microbiological risk assessment studies of S. aureus on rice cake in Korea.
  • Kento Koyama, Hidekazu Hokunan, Mayumi Hasegawa, Shuso Kawamura, Shigenobu Koseki
    APPLIED AND ENVIRONMENTAL MICROBIOLOGY 83 4 2017年02月 [査読有り][通常論文]
     
    Despite effective inactivation procedures, small numbers of bacterial cells may still remain in food samples. The risk that bacteria will survive these procedures has not been estimated precisely because deterministic models cannot be used to describe the uncertain behavior of bacterial populations. We used the Poisson distribution as a representative probability distribution to estimate the variability in bacterial numbers during the inactivation process. Strains of four serotypes of Salmonella enterica, three serotypes of enterohemorrhagic Escherichia coli, and one serotype of Listeria monocytogenes were evaluated for survival. We prepared bacterial cell numbers following a Poisson distribution (indicated by the parameter lambda, which was equal to 2) and plated the cells in 96-well microplates, which were stored in a desiccated environment at 10% to 20% relative humidity and at 5, 15, and 25 degrees C. The survival or death of the bacterial cells in each well was confirmed by adding tryptic soy broth as an enrichment culture. Changes in the Poisson distribution parameter during the inactivation process, which represent the variability in the numbers of surviving bacteria, were described by nonlinear regression with an exponential function based on a Weibull distribution. We also examined random changes in the number of surviving bacteria using a random number generator and computer simulations to determine whether the number of surviving bacteria followed a Poisson distribution during the bacterial death process by use of the Poisson process. For small initial cell numbers, more than 80% of the simulated distributions (lambda =2 or 10) followed a Poisson distribution. The results demonstrate that variability in the number of surviving bacteria can be described as a Poisson distribution by use of the model developed by use of the Poisson process. IMPORTANCE We developed a model to enable the quantitative assessment of bacterial survivors of inactivation procedures because the presence of even one bacterium can cause foodborne disease. The results demonstrate that the variability in the numbers of surviving bacteria was described as a Poisson distribution by use of the model developed by use of the Poisson process. Description of the number of surviving bacteria as a probability distribution rather than as the point estimates used in a deterministic approach can provide a more realistic estimation of risk. The probability model should be useful for estimating the quantitative risk of bacterial survival during inactivation.
  • Suguru Murashita, Shuso Kawamura, Shigenobu Koseki
    JOURNAL OF FOOD PROTECTION 80 1 164 - 168 2017年01月 [査読有り][通常論文]
     
    Methods for microbial inactivation are important in the food industry; however, conventional external heating (CH) reduces food quality. Accordingly, the nonthermal effects of ohmic heating (OH) on Bacillus subtilis spores in a sodium chloride aqueous solution at 101 degrees C (i.e., the boiling point), as well as the effects of electric field intensity and frequency during OH, were investigated. Survival kinetics were compared between OH and external CH. The inactivation effect on B. subtilis was greater for all electric field conditions (5, 10, and 20 V/cm) than for CH. In particular, 20 V/cm showed a significantly higher inactivation effect (P < 0.05) on B. subtilis than those of CH at 8, 10, 12, 14, and 16 min. The survival data were fitted to various primary kinetic models. In the Weibull model and the log-linear model, there were significant differences (P < 0.05) in the rate parameters delta and k(max) between OH at 20 V/cm and CH. However, there were no significant differences (P > 0.05) in survival kinetics between 20, 40, and 60 kHz; B. subtilis spores were inactivated more efficiently as the frequency increased. B. subtilis spores were almost completely inactivated at 14 to 16 min for the 60-kHz treatment, but spores were still alive at 20 and 40 kHz for the same treatment times. These results demonstrated that OH inactivates B. subtilis spores more effectively than CH. OH conditions with high electric field intensities and high frequencies resulted in efficient B. subtilis spore inactivation.
  • Kento Koyama, Hidekazu Hokunan, Mayumi Hasegawa, Shuso Kawamura, Shigenobu Koseki
    FOOD MICROBIOLOGY 60 49 - 53 2016年12月 [査読有り][通常論文]
     
    We investigated a bacterial sample preparation procedure for single-cell studies. In the present study, we examined whether single bacterial cells obtained via 10-fold dilution followed a theoretical Poisson distribution. Four serotypes of Salmonella enterica, three serotypes of enterohaemorrhagic Escherichia coli and one serotype of Listeria monocytogenes were used as sample bacteria. An inoculum of each serotype was prepared via a 10-fold dilution series to obtain bacterial cell counts with mean values of one or two. To determine whether the experimentally obtained bacterial cell counts follow a theoretical Poisson distribution, a likelihood ratio test between the experimentally obtained cell counts and Poisson distribution which parameter estimated by maximum likelihood estimation (MLE) was conducted. The bacterial cell counts of each serotype sufficiently followed a Poisson distribution. Furthermore, to examine the validity of the parameters of Poisson distribution from experimentally obtained bacterial cell counts, we compared these with the parameters of a Poisson distribution that were estimated using random number generation via computer simulation. The Poisson distribution parameters experimentally obtained from bacterial cell counts were within the range of the parameters estimated using a computer simulation. These results demonstrate that the bacterial cell counts of each serotype obtained via 10-fold dilution followed a Poisson distribution. The fact that the frequency of bacterial cell counts follows a Poisson distribution at low number would be applied to some single-cell studies with a few bacterial cells. In particular, the procedure presented in this study enables us to develop an inactivation model at the single-cell level that can estimate the variability of survival bacterial numbers during the bacterial death process. (C) 2016 Elsevier Ltd. All rights reserved.
  • Hidekazu Hokunan, Kento Koyama, Mayumi Hasegawa, Shuso Kawamura, Shigenobu Koseki
    JOURNAL OF FOOD PROTECTION 79 10 1680 - 1692 2016年10月 [査読有り][通常論文]
     
    We investigated the survival kinetics of Salmonella enterica and enterohemorrhagic Escherichia coli under various water activity (a(w)) conditions to elucidate the net effect of a(w) on pathogen survival kinetics and to pursue the development of a predictive model of pathogen survival as a function of a(w). Four serotypes of S. enterica (Stanley, Typhimurium, Chester, and Oranienburg) and three serotypes of enterohemorrhagic E. coli (E. coli 026, E. coli 0111, and E. coli 0157:H7) were examined. These bacterial strains were inoculated on a plastic plate surface at a constant relative humidity (RH) (22, 43, 58, 68; or 93% RH, corresponding to the a) or on a surface of almond kernels (a(w) 0.58), chocolate (a(w) 0.43), radish sprout seeds. (a(w) 0.58), or Cheddar cheese (a(w) 0.93) at 5, 15, or 25 C for up to 11 months. Under most conditions, the survival kinetics were nonlinear with tailing regardless of the storage a(w), temperature, and bacterial strain. For all bacterial serotypes, there were no apparent differences in pathogen survival kinetics on the plastic surface at a given storage temperature among the tested RH conditions, except for the 93% RH condition. Most bacterial serotypes were rapidly inactivated on Cheddar cheese when stored at 5 degrees C compared with their inactivation on chocolate, almonds, and radish sprout seeds. Distinct trends in bacterial survival kinetics were also observed between almond kernels and radish sprout seeds, even though the a(w)s of these two foods were not significantly different. The survival kinetics of bacteria inoculated on the plastic plate surface showed little correspondence to those of bacteria inoculated on food matrices at an identical a(w). Thus, these results demonstrated that, for low-a(w) foods and/or environments, a alone is insufficient to account for the survival kinetics of S. enterica and enterohemorrhagic E. coli.
  • Huijuan Zhou, Shuso Kawamura, Shigenobu Koseki, Toshinori Kimura
    Environmental Control in Biology 54 2 93 - 99 2016年 [査読有り][通常論文]
     
    Fresh-cut melon, 'Rupia red' cultivar, was packaged in snap-fit closed packages made from polylactic acid (PLA) and polyethylene terephthalate (PET) and stored at 4 and 10°C for 10 d. Changes in quality of fresh-cut melon, including weight loss, juice leakage, surface color, firmness, soluble solids content (SSC), pH, titratable acidity (TA), Vitamin C and sensory quality, were evaluated throughout the storage period. Overall quality of fresh-cut melon declined regardless of the packaging material. Melon cubes in both packages showed increases in weight loss, juice leakage and TA and they showed decreases in surface color (L∗, a∗, b∗), firmness, SSC, pH, Vitamin C and sensory evaluation. No significant difference in color, firmness, pH, TA or sensory evaluation was observed either of the packages at 4°C, but significant differences in color (L∗, a∗, b∗, ΔE) between the melon cubes in the two packages were found after 7 d of storage at 10°C. Due to higher water vapor and oxygen permeability, the PLA containers used in this study maintained overall quality of fresh-cut melon better than did the PET containers at 10°C during 10 d of storage. Bio-based PLA is a suitable alternative to petroleum-based PET for storage of fresh-cut melon.
  • Shigenobu Koseki, Nobutaka Nakamura, Takeo Shiina
    JOURNAL OF FOOD PROTECTION 78 4 819 - 824 2015年04月 [査読有り][通常論文]
     
    Under osmotic stress, bacterial cells uptake compatible solutes such as glycine-betaine to maintain homeostasis. It is unknown whether incompatible solutes exist that are similar in structure to compatible solutes but have adverse physiological effects on bacterial physiology. The objective of this study was to evaluate solute incompatibility of various amino acids against bacterial growth. Bacterial growth was evaluated by changes in optical density at 595 nm in peptone-yeast-glucose (PYG) broth. Twenty-three amino acids with L and/or D isomers were examined for the effect of bacterial growth inhibition. Among the various amino acids examined, D-tryptophan (similar to 40 mM) in PYG broth supplemented with 0 to 4% (wt/vol) salt inhibited the growth of Listeria monocytogenes, Salmonella enterica, and Escherichia coli 0157:117 at 25 degrees C. D-Tryptophan (30 to 40 mM) completely inhibited the growth of E. coli O157:H7 and Salmonella in the presence of >3% salt, but the growth of L. monocytogenes was not completely inhibited under the same conditions. Low concentrations of salt (0 to 2% NaCl) with D-tryptophan did not significantly inhibit the growth of all bacteria except L. monocytogenes, which was relatively inhibited at 0% NaCl. The effect of D-tryptophan differed depending on the bacterial species, illustrating the difference between gram-positive and gram-negative bacteria. These results indicate that the uptake of D-tryptophan as a compatible solute during osmotic stress may inhibit bacterial growth. The antibacterial effect of D-tryptophan found in this study suggests that D-tryptophan could be used as a novel preservative for controlling bacterial growth in foods.
  • D{\'i}az, E.O., Kawamura, S., Koseki, S.
    Agricultural Engineering International: CIGR Journal 2015 274 - 285 2015年01月 [査読有り][通常論文]
     
    © 2015, Int. Comm. of Agricultural and Biosystems Engineering. All rights reserved. This research involved a study of the physical properties of rough and brown rice of various types. The effect of kernel thickness on physical properties was analyzed. Fundamental physical properties, such as dimensions, mass, and frictional characteristics, were measured for different fractions of rough and brown rice of seven different varieties: Nanatsuboshi, Yumepirika, Oborozuki (Japonica type), IR-28, IR-50, IR-64 (Indica type), and NERICA-4 (NERICA type). Results showed that, in both rough and brown rice, the physical properties of the NERICA type showed a closer relationship with the Indica type than they did with the Japonica type. Moreover, statistical analysis indicated that the physical properties were affected by kernel thickness within each variety of rough and brown rice. Such information could be helpful in designing facilities and machines required for rice processing and storage.
  • Shigenobu Koseki, Nobutaka Nakamura, Takeo Shiina
    JOURNAL OF FOOD PROTECTION 78 1 104 - 110 2015年01月 [査読有り][通常論文]
     
    Bacterial pathogens such as Listeria monocytogenes, Escherichia coli O157:H7, Salmonella enterica, and Cronobacter sakazakii have demonstrated long-term survival in/on dry or low-water activity (a(w)) foods. However, there have been few comparative studies on the desiccation tolerance among these bacterial pathogens separately in a same food matrix. In the present study, the survival kinetics of the four bacterial pathogens separately inoculated onto powdered infant formula as a model low-a(w) food was compared during storage at 5, 22, and 35 degrees C. No significant differences in the survival kinetics between E. coli O157:H7 and L. monocyto genes were observed. Salmonella showed significantly higher desiccation tolerance than these pathogens, and C. sakazakii demonstrated significantly higher desiccation tolerance than all other three bacteria studied. Thus, the desiccation tolerance was represented as C. sakazakii > Salmonella > E. coli O157:H7 = L. monocytogenes. The survival kinetics of each bacterium was mathematically analyzed, and the observed kinetics was successfully described using the Weibull model. To evaluate the variability of the inactivation kinetics of the tested bacterial pathogens, the Monte Carlo simulation was performed using assumed probability distribution of the estimated fitted parameters. The simulation results showed that the storage temperature significantly influenced survival of each bacterium under the dry environment, where the bacterial inactivation became faster with increasing storage temperature. Furthermore, the fitted rate and shape parameters of the Weibull model were successfully modelled as a function of temperature. The numerical simulation of the bacterial inactivation was realized using the functions of the parameters under arbitrary fluctuating temperature conditions.
  • Koseki, S.
    Encyclopedia of Food Microbiology: Second Edition 2014年
  • 川崎 晋, 清水 茂雅, 小関 成樹, 稲津 康弘
    日本食品微生物学会雑誌 31 1 28 - 35 日本食品微生物学会 2014年 [査読有り][通常論文]
     
    The Salmonella growth was monitored in pasteurized and non- pasteurized milk using real-time PCR, and growth prediction model was constructed based on the results. Pasteurized and non- pasteurized milk were inoculated with Salmonella to a concentration of 104 CFU/ml, and the Salmonella growth was monitored for 168 hours at 4℃ to 35℃ using traditional culture method and real-time PCR. With real-time PCR, total-DNA was directly extracted from 1 ml of pasteurized and non- pasteurized milk, and the copy number of Salmonella invA was quantified and converted to the Salmonella cell count. The Salmonella cell counts estimated by traditional culture method and real-time PCR in pasteurized milk were very similar, and these results were reflecting the MRV predictive model. A predictive growth curve was constructed from the Salmonella cell count estimated using real-time PCR, and a relational expression for the maximum growth rate (μmax) and incubation temperature was derived using the square-root model. Comparison of μmax between pasteurized and non-pasteurized milk showed a slightly lower μmax of Salmonella for non- pasteurized milk compared to pasteurized milk, and the maximum cell concentration also tended to be lower for non- pasteurized milk. Application of the real-time PCR monitoring and predictive microbiological analysis enables rapid provision of a growth prediction formula that includes the effects of microbacterial flora and food matrices.
  • Miho Ohkochi, Shigenobu Koseki, Masaaki Kunou, Katsuaki Sugiura, Hirokazu Tsubone
    Journal of Food Protection 76 9 1549 - 1556 2013年09月 [査読有り][通常論文]
     
    The growth kinetics of Listeria monocytogenes and natural flora in commercially produced pasteurized liquid egg was examined at 4.1 to 19.4°C, and a growth simulation model that can estimate the range of the number of L. monocytogenes bacteria was developed. The experimental kinetic data were fitted to the Baranyi model, and growth parameters, such as maximum specific growth rate (μmax), maximum population density (Nmax), and lag time (λ), were estimated. As a result of estimating these parameters, we found that L. monocytogenes can grow without spoilage below 12.2°C, and we then focused on storage temperatures below 12.2°C in developing our secondary models. The temperature dependency of the mmax was described by Ratkowsky's square root model. The Nmax of L. monocytogenes was modeled as a function of temperature, because the Nmax of L. monocytogenes decreased as storage temperature increased. A tertiary model of L. monocytogenes was developed using the Baranyi model and μmax and Nmax secondary models. The ranges of the numbers of L. monocytogenes bacteria were simulated using Monte Carlo simulations with an assumption that these parameters have variations that follow a normal distribution. Predictive simulations under both constant and fluctuating temperature conditions demonstrated a high accuracy, represented by root mean square errors of 0.44 and 0.34, respectively. The predicted ranges also seemed to show a reasonably good estimation, with 55.8 and 51.5% of observed values falling into the prediction range of the 25th to 75th percentile, respectively. These results suggest that the model developed here can be used to estimate the kinetics and range of L. monocytogenes growth in pasteurized liquid egg under refrigerated temperature. Copyright © 2013, International Association for Food Protection.
  • Shige Koseki
    FOOD CONTROL 29 2 416 - 421 2013年02月 [査読有り][通常論文]
     
    An alternative predictive model for microbial inactivation and a novel web-based tool for the application of predictive microbiology are reviewed in this paper. The developed model, based on probabilistic concepts, enabled the identification of minimum processing conditions necessary to obtain a required log reduction, regardless of the underlying inactivation kinetics. The model also provides the probability distribution of the inactivation effect. The revised web-tool, the MRV (Microbial Responses Viewer), provides information concerning growth/no growth boundary conditions and the specific growth rates of queried microorganisms. The MRV enables users to retrieve microbial growth/no growth information intuitively. Using the MRV, food processors can easily identify appropriate food design and processing conditions. (C) 2012 Elsevier Ltd. All rights reserved.
  • Real-Time PCRによる生乳中のサルモネラ・リステリア増殖挙動解析
    川崎 晋, 清水 茂雅, 小関 成樹, 稲津 康弘, 川本 伸一
    日本食品衛生学会学術講演会講演要旨集 104回 111 - 111 (公社)日本食品衛生学会 2012年09月 [査読有り][通常論文]
  • Shige Koseki, Junko Nonaka
    APPLIED AND ENVIRONMENTAL MICROBIOLOGY 78 17 6103 - 6112 2012年09月 [査読有り][通常論文]
     
    The objective of this study was to develop a probabilistic model to predict the end of lag time (lambda) during the growth of Bacillus cereus vegetative cells as a function of temperature, pH, and salt concentration using logistic regression. The developed lambda model was subsequently combined with a logistic differential equation to simulate bacterial numbers over time. To develop a novel model for lambda, we determined whether bacterial growth had begun, i.e., whether lambda had ended, at each time point during the growth kinetics. The growth of B. cereus was evaluated by optical density (OD) measurements in culture media for various pHs (5.5 similar to 7.0) and salt concentrations (0.5 similar to 2.0%) at static temperatures (10 similar to 20 degrees C). The probability of the end of lambda was modeled using dichotomous judgments obtained at each OD measurement point concerning whether a significant increase had been observed. The probability of the end of lambda was described as a function of time, temperature, pH, and salt concentration and showed a high goodness of fit. The lambda model was validated with independent data sets of B. cereus growth in culture media and foods, indicating acceptable performance. Furthermore, the lambda model, in combination with a logistic differential equation, enabled a simulation of the population of B. cereus in various foods over time at static and/or fluctuating temperatures with high accuracy. Thus, this newly developed modeling procedure enables the description of lambda using observable environmental parameters without any conceptual assumptions and the simulation of bacterial numbers over time with the use of a logistic differential equation.
  • S. Koseki, M. L. Tamplin, J. P. Bowman, T. Ross, T. A. McMeekin
    LETTERS IN APPLIED MICROBIOLOGY 54 3 203 - 208 2012年03月 [査読有り][通常論文]
     
    Aims: To elucidate the potential use of microelectrode ion flux measurements to evaluate bacterial responses to heat treatment. Methods and Results: Escherichia coli K12 Was used as a test bacterium to determine whether various heat treatments (55-70 degrees C for 15 min) affected net ion flux across E coli cell membranes using the MIFE (TM) system to measure net K+ fluxes. No difference in K+ fluxes was observed before and after heat treatments regardless of the magnitude of the treatment. Applying hyperosmotic stress (3% NaCl w/v) during flux measurement led to a net K+ loss from the heat treated E cote cells below 65 degrees C as Well as from nonheated cells. In contrast, with E. coli cells treated at and above 65 degrees C, hyperosmotic stress disrupted the pattern of K+ flux observed at lower temperatures and resulted in large flux noise with random scatter. This phenomenon Was particularly apparent above 70 degrees C. Although E. cote cells lost the potential to recover and grow at and above 62 degrees C, K+ flux disruption was not clearly observed until 68 degrees C was reached. Conclusions: No changes in net K+ flux from heat stressed E. coli cells were observed directly as a result of thermal treatments. However, regardless of the magnitude of heat treatment above 55 degrees C, loss of viability indicated by enrichment culture correlated with disrupted K+ fluxes when previously heated cells were further challenged by imposing hyperosmotic stress during flux measurement. This two-stage process enabled evaluation of the lethality of heat treated bacterial cells within 2 h and may be an alternative and more rapid method to confirm the lethality of heat treatment. Significance and Impact of the Study: The ability to confirm the lethality of thermal treatments and to specify minimal time/temperature combinations by a nonculture-dependent test offers an alternative system to culture based methods
  • Shigenobu Koseki, Yasuko Mizuno, Kazutaka Yamamoto
    JOURNAL OF FOOD PROTECTION 74 9 1536 - 1542 2011年09月 [査読有り][通常論文]
     
    The route of pathogen contamination (from roots versus from leaves) of spinach leaves was investigated with a hydroponic cultivation system. Three major bacterial pathogens, Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes, were inoculated into the hydroponic solution, in which the spinach was grown to give concentrations of 10(6) and 10(3) CFU/ml. In parallel, the pathogens were inoculated onto the growing leaf surface by pipetting, to give concentrations of 10(6) and 10(3) CFU per leaf. Although contamination was observed at a high rate through the root system by the higher inoculum (10(6) CFU) for all the pathogens tested, the contamination was rare when the lower inoculum (10(3) CFU) was applied. In contrast, contamination through the leaf occurred at a very low rate, even when the inoculum level was high. For all the pathogens tested in the present study, the probability of contamination was promoted through the roots and with higher inoculum levels. The probability of contamination was analyzed with logistic regression. The logistic regression model showed that the odds ratio of contamination from the roots versus from the leaves was 6.93, which suggested that the risk of contamination from the roots was 6.93 times higher than the risk of contamination from the leaves. In addition, the risk of contamination by L. monocytogenes was about 0.3 times that of Salmonella enterica subsp. enterica serovars Typhimurium and Enteritidis and E. coli O157:H7. The results of the present study indicate that the principal route of pathogen contamination of growing spinach leaves in a hydroponic system is from the plant's roots, rather than from leaf contamination itself.
  • Shigenobu Koseki, Yasuko Mizuno, Susumu Kawasaki, Kazutaka Yamamoto
    JOURNAL OF FOOD PROTECTION 74 9 1543 - 1546 2011年09月 [査読有り][通常論文]
     
    No information has been available on the prevalence of pathogens in fresh produce in Japan. In the present study, information was collected on the occurrence of contamination by Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes in iceberg lettuce in a Japanese retail store. A total of 419 samples of lettuce that had been harvested in different districts and/or by different producers from July 2008 to March 2009 were examined. A multiplex PCR method was used to simultaneously identify the three bacterial pathogens. No pathogenic bacteria, including Salmonella, E. coli O157:H7, and L. monocytogenes, were detected from any of the samples with this highly sensitive and validated procedure. The aerobic bacteria plate counts and coliform bacteria counts in lettuce throughout the examination period did not show any seasonal trends, and the numbers were comparable to those reported by others from around the world. Based on the results of this study, we concluded that none of the three major pathogens were present in this limited survey of iceberg lettuce sold by a retailer in Japan.
  • Shige Koseki, Yasuko Mizuno, Itaru Sotome
    APPLIED AND ENVIRONMENTAL MICROBIOLOGY 77 3 1021 - 1032 2011年02月 [査読有り][通常論文]
     
    The objective of the present study was to develop a mathematical model of pathogenic bacterial inactivation kinetics in a gastric environment in order to further understand a part of the infectious dose-response mechanism. The major bacterial pathogens Listeria monocytogenes, Escherichia coli O157: H7, and Salmonella spp. were examined by using simulated gastric fluid adjusted to various pH values. To correspond to the various pHs in a stomach during digestion, a modified logistic differential equation model and the Weibull differential equation model were examined. The specific inactivation rate for each pathogen was successfully described by a square-root model as a function of pH. The square-root models were combined with the modified logistic differential equation to obtain a complete inactivation curve. Both the modified logistic and Weibull models provided a highly accurate fitting of the static pH conditions for every pathogen. However, while the residuals plots of the modified logistic model indicated no systematic bias and/or regional prediction problems, the residuals plots of the Weibull model showed a systematic bias. The modified logistic model appropriately predicted the pathogen behavior in the simulated gastric digestion process with actual food, including cut lettuce, minced tuna, hamburger, and scrambled egg. Although the developed model enabled us to predict pathogen inactivation during gastric digestion, its results also suggested that the ingested bacteria in the stomach would barely be inactivated in the real digestion process. The results of this study will provide important information on a part of the dose-response mechanism of bacterial pathogens.
  • Shigenobu Koseki, Yoshiko Takizawa, Satoko Miya, Hajime Takahashi, Bon Kimura
    JOURNAL OF FOOD PROTECTION 74 2 176 - 187 2011年02月 [査読有り][通常論文]
     
    The growth kinetics of Listeria monocytogenes and natural flora (NF) in minced tuna from 2 to 30 degrees C were examined, and a simultaneous growth model was developed. The inhibiting effect of the NF on the growth of L. monocytogenes was examined by inoculating different levels of NF isolated from the minced tuna. The kinetic data were fitted to the Baranyi model and estimated the growth parameters such as specific growth rate (mu(max)), maximum population density (N-max), and lag time. The temperature and inoculated NF dependency on the mu(max) of L. monocytogenes and NF were described by modified Ratkowsky's square-root model. As the initial NF level increased, the slopes of the square-root models were decreased for both L. monocytogenes and NF. The N-max of L. monocytogenes was described as a function of temperature and inoculated NF level. Simultaneous growth prediction of L. monocytogenes and NF under constant temperature conditions was examined by using the differential equations based on the Baranyi model with the effect of interspecies competition substituted into the developed mu(max) and N-max models. The root mean square errors between the model prediction and the observation for L. monocytogenes and NF were 0.42 and 0.34, respectively. Predictive simulation under fluctuating temperature conditions also demonstrated a high accuracy of simultaneous prediction for both L. monocytogenes and NF, representing the root mean square errors of 0.19 and 0.34, respectively. These results illustrate that the developed model permits accurate estimation of the behavior of L. monocytogenes in minced tuna under real temperature history until consumption.
  • Tom McMeekin, Mark Tamplin, Tom Ross, Shigenobu Koseki
    AUSTRALIAN JOURNAL OF DAIRY TECHNOLOGY 65 2 91 - 97 2010年08月 [査読有り][通常論文]
     
    Herein we describe systems and technologies for the application of predictive models and the development of growth boundary models. The latter are supported by systematic analysis of the literature and are now used in risk assessments including those cold tolerant pathogens in minimally processed foods including dairy products. To promote further application of predictive models in the dairy industry and potential triple bottom line benefits we strongly advocate collaboration and integration of R&D at several levels.
  • Shige Koseki
    INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY 134 1-2 75 - 82 2009年08月 [査読有り][通常論文]
     
    ComBase is a large database of microbial responses to food environments and has attracted the attention of many researchers and food processors. Although ComBase contains a vast amount of data, it is not easy to obtain desired information from the retrieved data. In the present study, we developed a new ComBase-derived database (Microbial Responses Viewer, MRV) consisting of microbial growth/no growth data. The response was defined as representing "growth" if a significant increase in bacterial concentration (>1.0 log(10)) was observed. Alternatively, "growth" was defined as a positive value of the specific growth rate. The growth/no growth data of nineteen different microorganisms were extracted from all the data in ComBase comprising 29 kinds of microorganism. Furthermore, the specific growth rate of each microorganism was modelled as a function of temperature, pH, and water activity (a(w)) using a Poisson log-linear model, which is a family of generalized linear models (GLMs). For 16 of the 19 microorganisms, the specific growth/death rate was successfully modelled as a function of temperature, pH, and a(w) using GLM. The specific growth rate was illustrated using a two-dimensional contour plot with growth/no growth data. MRV provides information concerning growth/no growth boundary conditions and the specific growth rates of queried microorganisms. Using MRV, food processors can easily find the appropriate food design and processing conditions. This database will contribute to the efficient and safe production and distribution of processed foods. (C) 2008 Elsevier B.V. All rights reserved.
  • Itaru Sotome, Makiko Takenaka, Shigenobu Koseki, Yukio Ogasawara, Yoshitaka Nadachi, Hiroshi Okadome, Seiichiro Isobe
    LWT-FOOD SCIENCE AND TECHNOLOGY 42 6 1035 - 1040 2009年07月 [査読有り][通常論文]
     
    A heating system using superheated steam (SHS) and a spray of hot water microdroplets (WMD) has been developed to prevent drying of food material during SHS heating. Blanching of potato was examined with the new system (SHS + WMD), SHS, and hot water. In SHS + WMD heating, a mixture of SHS at 115 degrees C, 2.46 kg/h flow rate and hot water at 0.54 kg/h was used. In SHS heating, the flow rate and temperature of the SHS were 3.0 kg/h and 115 degrees C. The temperature of the hot water was approximately 100 degrees C. Potato tissue processed with hot water became soft and brittle, and its brightness and chromatic quality decreased due to absorption of water and dissolution of solid content to the water. In contrast, these quality changes were prevented in SHS + WMD and SHS heating. Heat transfer by SHS was enhanced by the presence of WMD, presumably because the water layer formed on the potato by condensation of SHS was stirred and its thermal resistance was decreased by collisions of WMD with the potato. The mass of potato processed with SHS + WMD was almost constant during the heating, while the relative mass of potato processed with SHS decreased to 96.7% with 16 min of heating. (C) 2009 Elsevier Ltd. All rights reserved.
  • Shige Koseki, Maki Matsubara, Kazutaka Yamamoto
    APPLIED AND ENVIRONMENTAL MICROBIOLOGY 75 7 1885 - 1891 2009年04月 [査読有り][通常論文]
     
    A probabilistic model for predicting Enterobacter sakazakii inactivation in trypticase soy broth (TSB) and infant formula (IF) by high-pressure processing was developed. The modeling procedure is based on a previous model (S. Koseki and K. Yamamoto, Int. J. Food Microbiol. 116: 136-143, 2007) that describes the probability of death of bacteria. The model developed in this study consists of a total of 300 combinations of pressure (400, 450, 500, 550, or 600 MPa), pressure-holding time (1, 3, 5, 10, or 20 min), temperature (25 or 40 degrees C), inoculum level (3, 5, or 7 log(10) CFU/ml), and medium (TSB or IF), with each combination tested in triplicate. For each replicate response of E. sakazakii, survival and death were scored with values of 0 and 1, respectively. Data were fitted to a logistic regression model in which the medium was treated as a dummy variable. The model predicted that the required pressure-holding times at 500 MPa for a 5-log reduction in IF with 90% achievement probability were 26.3 and 7.9 min at 25 and 40 degrees C, respectively. The probabilities of achieving 5-log reductions in TSB and IF by treatment with 400 MPa at 25 degrees C for 10 min were 92 and 3%, respectively. The model enabled the identification of a minimum processing condition for a required log reduction, regardless of the underlying inactivation kinetics pattern. Simultaneously, the probability of an inactivation effect under the predicted processing condition was also provided by taking into account the environmental factors mentioned above.
  • Daiki D. Horikawa, Ken-Ichi Iwata, Kiyoshi Kawai, Shigenobu Koseki, Takashi Okuda, Kazutaka Yamamoto
    ZOOLOGICAL SCIENCE 26 3 238 - 242 2009年03月 [査読有り][通常論文]
     
    High hydrostatic pressure (HHP) can induce physical changes in DNA, proteins, and lipids, causing lethal or sublethal damage to organisms. However, HHP tolerance of animals has not been studied sufficiently. In this study, HHP tolerance of four species of invertebrate anhydrobiotes (the tardigrade Milnesium tardigradum, a nematode species in the family Plectidae, larvae of Polypedilum vanderplanki, and cysts of Artemia franciscana), which have the potential to enter anhydrobiosis upon desiccation, were investigated by exposing them to 1.2 GPa for 20 minutes. This exposure killed the anhydrobiotes in their ordinary hydrated state, but did not affect their survival in the anhydrobiotic state. The results indicated that the hydrated anhydrobiotes were vulnerable to HHP, but that HHP of 1.2 GPa was not sufficient to kill them in anhyrdobiosis.
  • Shigenobu Koseki, Yasuko Mizuno, Kazutaka Yamamoto
    FOOD MICROBIOLOGY 25 2 288 - 293 2008年02月 [査読有り][通常論文]
     
    This study examined the inactivation of Listeria monocytogenes in milk by high-pressure processing (HPP) and bacterial recovery during storage after HPP. We developed a technique to inhibit the bacterial recovery during storage after HPP (550 MPa for 5 min) using a mild-heat treatment (30-50 degrees C). Various mild-heat treatments were conducted following HPP to investigate the condition on which the bacterial recovery was prevented. Immediately after HPP of 550 MPa at 25 degrees C for 5 min, no L. monocytogenes cells were detected in milk regardless of the inoculum levels (3, 5, and 7 log(10) CFU/ml). However, the number of L. monocytogenes cells increased by > 8 log(10) CFU/ml regardless of the inoculum levels after 28 days of storage at 4 degrees C. Significant recovery was observed during storage at 25 degrees C; the bacterial number increased by > 8 log(10) CFU/ml after 3 days of storage in the case of an initial inoculum level of 7 and 5 log(10) CFU/ml. Even in the case of an initial inoculum level of 3 log(10) CFU/ml, the bacterial number reached the level of 8 log(10) CFU/ml after 7 days of storage. No bacterial recovery was observed with storage at 37 degrees C for 28 days. Milk samples were treated by various mild-heat treatments (30-50 degrees C for 5-240 min) following HPP of 550 MPa at 25 degrees C for 5 min, and then stored at 25 degrees C for 70 days. The mild-heat treatment (e.g., 37 degrees C for 240min or 50 degrees C for 10min) inhibited the recovery of L. monocytogenes in milk after HPP. No recovery of L. monocytogenes in milk was observed during 70-day storage at 25 degrees C in samples that received mild-heat treatments such as mentioned above following HPP (550 MPa for 5 min). Moreover, the mild-heat treatment conditions (temperature and holding time) required to inhibit the recovery of L. monocytogenes in milk was modelled using a logistic regression procedure. The predicted interface of recovery/no recovery can be used to calculate the mild-heat treatment condition to control bacterial recovery during storage at 25 degrees C after HPP (550 MPa for 5 min). The results in this study would contribute to enhance the safety of high-pressure-processed milk. (C) 2007 Elsevier Ltd. All rights reserved.
  • 小関 成樹
    農業機械学会誌 70 Supplement 453 - 454 The Japanese Society of Agricultural Machinery and Food Engineers 2008年
  • 小関 成樹, 津田 升子, 五十部 誠一郎
    農業機械学会誌 70 445 - 446 The Japanese Society of Agricultural Machinery and Food Engineers 2008年
  • Shigenobu Koseki, Yasuko Mizuno, Kazutaka Yamamoto
    INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY 119 3 300 - 307 2007年11月 [査読有り][通常論文]
     
    This study examined bacterial recovery on sliced cooked ham that was inoculated with Listeria monocytogenes, treated by high pressure processing (HPP) and then stored at 10 degrees C for 70 days. The number of L. monocytogenes on the ham inoculated with 5 log(10) CFU/g was initially reduced by HPP at 500 MPa for 10 min to below the detectable level (10 CFU/g). However, the bacterial count gradually increased during storage, and exceeded the initial inoculum level at the end of the 70-day period, having risen by 7-8 log(10) CFU/g. A novel predictive model was therefore developed to estimate the recovery of L. monocytogenes during storage after HPP. Recovery of L. monocytogenes was defined as the detection of > 10(2) CFU/g bacteria, in view of the relevant food safety objectives of L. monocytogenes. At each 14-day sampling session, the ham was scored as either 1 or 0 indicating bacterial recovery or no bacterial recovery, respectively. The data were then subjected to a simple linear logistic regression model, which provided a good fit as indicated by the performance statistics. Using this model, we estimated the minimum HPP conditions necessary for the required storage periods. Additionally, as the developed model was based on logistic regression, the probability of the recovery of L. monocytogenes during storage after HPP was estimated. Our model not only calculated the appropriate shelf life and process conditions, but also provided a method for evaluating the risk of the recovery of pathogenic bacteria during storage. (C) 2007 Elsevier B.V All rights reserved.
  • Shigenobu Koseki, Seiichiro Isobe
    JARQ-JAPAN AGRICULTURAL RESEARCH QUARTERLY 41 4 273 - 282 2007年10月 [査読有り][通常論文]
     
    The demand for fresh salad vegetables, such as iceberg lettuce, has increased worldwide in recent years. Numerous sanitizers have been examined for their effectiveness in killing or removing pathogenic bacteria on fresh produce. However, most of the sanitizers are made from the dilution of condensed solutions which involves some risk in handling and is troublesome. A sanitizer that is not produced from the dilution of a hazardous condensed solution is required for practical use. Electrolyzed water and ozonated water were investigated for bactericidal effects on fresh-cut produce as a convenient and safe alternative sanitizer. Although the efficacy of acidic electrolyzed water (AcEW) as a sanitizing agent was dependent on the kind of produce treated, AcEW could be sufficiently effective to offer an alternative solution to conventional sanitizers, such as sodium hypochlorite solution (150 ppm). A novel produce-washing procedure using a combination of alkaline electrolyzed water (AlEW), AcEW and mild heat demonstrated significant bactericidal effect compared with the treatment with ambient temperature. Besides the bactericidal effect, the progress of browning on lettuce was suppressed by using mild heat treatment. Furthermore, as a novel usage of AcEW, we examined the use of AcEW-ice for preserving vegetables. AcEW-ice inactivated the spoilage and pathogenic bacteria on lettuce and reduced the temperature of lettuce during storage.
  • Shigenobu Koseki, Kazutaka Yamamoto
    INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY 116 1 136 - 143 2007年05月 [査読有り][通常論文]
     
    The survival/death interface model was developed for prediction of inactivation of Listeria monocytogenes by high pressure processing (HPP). The model was derived from data sets comprising 360 combinations of environmental factors such as pressure (200, 300 400, and 500 MPa), pressure-holding time (1, 3, 5, 10, 20, 30 min), pH (3, 4, 5, 6, 7), and inoculum level (3, 5, 7 log(10) CFU/ml). The determination of survival/death of L. monocytogenes after HPP was confirmed by the presence/absence of colony forming ability on non-selective agar plates after 30 days of incubation at 20 degrees C in broth to take into account recovery of HPP-induced injured cells. The developed linear logistic model with time logarithmically transformed gave a degree of agreement between probabilities predicted by the fitted model and all observations as 99.3% concordant. The model provided a good fit to the data as shown by performance statistics. The developed interface model in the present study provided requisite process conditions for the target effect of HPP on L. monocytogenes. In addition to using the simple linear logistic model, a polynomial logistic model was also fitted to the data where pressure-holding time was not logarithmically transformed. That model did not produce a better fit to the data and resulted in some potentially misleading predictions. Optimization of HPP could be accomplished using the model developed in this study. Furthermore, choice in processing factors allows for processing flexibility in HPP and specifies the process criteria that are incorporated into the HACCP plan. (c) 2007 Elsevier B.V. All rights reserved.
  • Shigenobu Koseki, Kazutaka Yamamoto
    INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY 116 2 275 - 282 2007年05月 [査読有り][通常論文]
     
    The inactivation kinetics of Escherichia coli (ATCC 25922) during high pressure processing (HPP) was examined from 200 to 400 MPa in 50 MPa increments at 15 degrees C. Although the time course of HPP-induced E. coli inactivation in 0.1% peptone water successfully fitted the Weibull function, this procedure involved curve fitting, and not prediction. The objective of this study was to develop a novel HPP-induced microbial inactivation model to simulate the inactivation kinetics under various pressure conditions. The maximum inactivation rate during HPP was calculated from the inactivation curves at different pressure conditions on a semi-log plot. The relationship between the square root of the absolute value of the inactivation rate (root k(max)) and treatment pressure was linear (R-2=0.99). The linear relationship between root k(max) and treatment pressure also successfully described independent data from other studies in the literature. Overall, the newly developed differential equation model, into which was substituted the square root function of the inactivation rate, was capable of simulating the inactivation kinetics during HPP at constant pressure. Additionally, the model could successfully describe the inactivation kinetics during HPP using other researchers' data. The accuracy of prediction of the new model was comparable to that derived from Weibull or modified Gompertz fitting to the observed data. Furthermore, the new model could successfully simulate the inactivation kinetics during dynamic pressure conditions, which included come-up time, changes in holding pressure during treatment, and pressure-release time. Moreover, the effect of pulsed pressure treatment was also simulated successfully using this model. Therefore, the modeling procedure presented in this study will contribute to the advancement of predictive modeling for HPP-induced microbial inactivation. (c) 2007 Elsevier B.V All rights reserved.
  • Shigenobu Koseki, Kazutaka Yamamoto
    INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY 115 1 43 - 47 2007年04月 [査読有り][通常論文]
     
    Inactivation of Listeria monocytogenes (108 CFU/ml) by high hydrostatic pressure (HHP) from 400 to 600 MPa at 25 degrees C for 10 min was investigated with various concentrations of sodium chloride, sucrose, and sodium phosphate buffer solutions. Sodium chloride significantly inhibited HHP-induced inactivation of L. monocytogenes at concentrations higher than 2.6 M. A low concentration of sodium chloride within 1.7 M had no effect on HHP-induced inactivation. Almost complete inactivation at relatively low sodium chloride concentration solution was observed with treatments above 500 MPa. Sucrose also significantly inhibited HHP-induced inactivation of L. monocytogenes when greater than 1.2 M sucrose solutions were used. HHP-treatment at 400 MPa reduced the number of L. monocytogenes in 1.2 M, 1.5 M, and 1.8 M sucrose solutions by 4.8, 2.0, and 0.7 log cycles, respectively. Higher pressure, did not yield significant reductions. Sodium phosphate buffer significantly inhibited HHP-induced inactivation of L. monocytogenes . In particular, 1 M phosphate buffer completely inhibited HHP-induced inactivation even at 600 MPa. HHP-treatment at 400 MPa reduced the number of L. monocytogenes in 0.1 M, 0.25 M, and 0.5 M phosphate buffer solutions by 5.6, 4.1, and 3.2 log cycles, respectively. The effect of HHP-induced inactivation of L. monocytogenes in the three kinds of solution was evaluated by adjusting water activity (a(w)). However, the baroprotective effect differed depending on the kind of solute even at the same a(w). This result showed no consistent correlation between a, and solute concentration in terms of the baroprotective effect. As an alternative approach, saturation of suspension solution was used for evaluating the effect of HHP-induced inactivation of L. monocytogenes. As the saturation of suspension media increased, the effect of HHP-induced inactivation of L. monocytogenes decreased regardless of the kinds of solute. The saturation of solution would be an alternative parameter of inhibition in terms of HHP-induced inactivation of bacteria. (c) 2006 Elsevier B.V. All rights reserved.
  • Shigenobu Koseki, Kazutaka Yamamoto
    INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY 111 2 175 - 179 2006年09月 [査読有り][通常論文]
     
    The effect of pH and solute concentration of suspension media on high hydrostatic pressure (HHP) induced inactivation of Listeria monocytogenes (approximate 10(8) CFU/ml) was investigated by the using treatment between 300 MPa and 600 MPa at 25 degrees C for 10 min. The suspension media used in this study represented different concentrations (0.1% to 10%) of buffered peptone water (BPW) with an adjusted pH of 4 to 7. An increase in the concentration of BPW resulted in a decreased HHP-induced inactivation of L. monocytogenes that was dependent on the pH of the medium. HHP-treatment at 300 MPa showed no bactericidal effect at neutral pH regardless of the BPW concentration. When the pH of BPW (0.1% to 5%) was reduced to 4, L. monocytogenes was completely inactivated (more than an 8 log cycle reduction) with a HHP-treatment of at least 3 00 MPa. HHP-treatment above 400 MPa completely inactivated L. monocytogenes in a relatively dilute BPW (0.1 % and 1%) with an adjusted pH below 6. While only a 2 log cycle reduction was observed in 10% BPW at the pH ranging from 5 to 7 after treatment with 600 MPa, L. monocytogenes in 10% BPW at pH 4 was completely inactivated. Even though a significant bactericidal effect of HHP-treatment was not observed when applied with a low pressure such as 300 MPa or suspended in higher BPW at neutral pH, a reduction of the pH greatly affected the HHP-induced inactivation of L. monocytogenes. These results indicated that information concerning the pH of food or media would greatly assist an optimization of HHP-treatment for the inactivation of bacteria. (c) 2006 Elsevier B.V. All rights reserved.
  • Shigenobu Koseki, Kazutaka Yamamoto
    INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY 110 1 108 - 111 2006年07月 [査読有り][通常論文]
     
    Escherichia coli ATCC 25922 in phosphate buffered saline solution (PBS, pH 7.1, 108 CFU/ml) was inactivated by high hydrostatic pressure (HHP, 400 to 600 MPa) treatment at 25 degrees C for 10 min. Colonies of E. coli were not detected on non-selective plate count agar immediately after a HHP-treatment of at least 550 MPa. E. coli subjected to at least 500 MPa in PBS were incubated at 4, 25, and 37 degrees C for 120 h. No colonies were detected on plate count agar throughout the 120-h incubation period at 4 or 37 degrees C. In contrast, the number of E coli during storage at 25 degrees C increased from an undetectable level (< 1 CFU/ml) to the level of initial cell counts regardless of the treatment pressure level. The recovery in PBS required a maximum time of 48 h, while the period during which cell numbers remained at an undetectable level increased from 24 to 72 h as the treatment pressure increased. E. coli treated at 550 and 600 MPa in PBS were inoculated into trypticase soy broth (TSB) and stored at 4, 25, and 37 degrees C for 120 h. No recovery was recorded in TSB during the 120-h storage at 37 degrees C. In contrast, the number of E.coli during storage at 25 degrees C in TSB increased beyond the level of initial cell counts regardless of the treatment pressure level. The recovery of cell numbers observed in TSB was faster than that in PBS samples, as bacterial growth in TSB assisted faster recovery. When the incubation temperature in PBS was shifted to 25 degrees C after 120-h at 4 or 37 degrees C, recovery of E. coli was observed in samples shifted from 4 to 25 degrees C regardless of the treatment pressure. However, the time during which cell numbers remained at an undetectable level was extended by increasing the level of treatment pressure, and recovery required a maximum time of 48 h. On the other hand, no recovery was observed with HHP-treated E. coli subjected to an incubation temperature shift from 37 to 25 degrees C. This study indicates that an appropriate incubation temperature after HHP-treatment is needed to optimize the recovery of HHP-injured bacteria and thus prevent overestimation of the lethal effect of HHP-treatment. (c) 2006 Elsevier B.V. All rights reserved.
  • 五月女 格, 鈴木 啓太郎, 小関 成樹, 坂本 晋子, 竹中 真紀子, 小笠原 幸雄, 名達 義剛, 五十部 誠一郎
    日本食品科学工学会誌 : Nippon shokuhin kagaku kogaku kaishi = Journal of the Japanese Society for Food Science and Technology 53 9 451 - 458 Japanese Society for Food Science and Technology 2006年 [査読有り][通常論文]
     
    115℃のアクアガス，115℃過熱水蒸気ならびに100℃の熱水にてジャガイモの加熱処理を行った．加熱媒体からジャガイモへの熱伝達率を測定した結果，アクアガスの熱伝達率が最も高かったが，加熱処理中のジャガイモ中心部の温度履歴に加熱媒体間の差は見られなかった．また加熱処理によるジャガイモ中のペルオキシダーゼ失活の進行にも加熱媒体間の差は見られなかった．この原因は，いずれの加熱媒体による加熱処理においてもジャガイモ表面における熱伝達は十分に大きく，ジャガイモ内部温度変化はジャガイモ自身の熱拡散係数に律速されていたためであったことが，ジャガイモ内部における熱伝導シミュレーションの結果から確認された．<BR>また，それぞれの加熱媒体により加熱処理されたジャガイモの品質を比較した結果，アクアガスならびに過熱水蒸気により加熱処理されたジャガイモが熱水にて処理されたジャガイモと比較して，硬さも保たれ色彩も良好であった．走査型電子顕微鏡によるジャガイモ微細構造の観察結果，熱水により加熱処理されたジャガイモにおいては熱水への固形成分の溶出が推察された．このことから固形成分の溶出の有無が加熱処理されたジャガイモの品質に影響を及ぼしたと考えられた．またアクアガスによる加熱処理では過熱水蒸気処理と比較して質量減少を抑制することができた．更に，アクアガス処理によりジャガイモ表面に塗布した<I>B. subtilis</I>胞子を死滅させることが可能であった．<BR>以上のことからアクアガスを用いることにより，熱水による加熱処理と比較して良好な品質にて，また過熱水蒸気処理と比較して小さな質量減少にて，ジャガイモのブランチングを行うことが可能であると結論付けられた．またアクアガスを用いて加熱処理されたジャガイモを無菌状態にて保存することにより，高品質なジャガイモの長期間貯蔵が可能になると期待された．今後はジャガイモの酵素失活に必要な加熱温度条件等を詳細に検討し，アクアガスにより加熱処理されたジャガイモの貯蔵性ならびに貯蔵されたジャガイモの品質変化について解明していく予定である．
  • S Koseki, S Isobe
    JOURNAL OF FOOD PROTECTION 69 1 154 - 160 2006年01月 [査読有り][通常論文]
     
    We examined the effect of ozonated water treatment on microbial control and quality of cut iceberg lettuce (Lactuca sativa L.). Fresh-cut lettuce was washed in ozonated water (3, 5, and 10 ppm) for 5 min at ambient temperature. The native bacterial population on the lettuce declined in response to a rise in ozone concentration. However, there was no further bacterial reduction (1.4 log CFU/g) above 5 ppm ozone. Although ozonated water treatment increased the phenylalanine ammonia lyase (PAL) activity of the lettuce stored at 10 degrees C compared with the water wash treatment after 1 day of storage, the concentration of ozone did not affect PAL activity. The a* value of the residue of the lettuce methanol extracts, which reflects the extent of browning, increased dramatically in lettuce treated with 10 ppm ozonated water compared with other treatments. Treatment with 3 or 5 ppm ozonated water resulted in more rapid changes in the a* value than after the water treatment. The combined treatment of hot water (50 degrees C, 2.5 min) followed by ozonated water (5 ppm, 2.5 min) had the same bactericidal effect as treatment with ozonated water (5 ppm, 5 min) or sodium hypochlorite (NaOCI, 200 ppm, 5 min), giving a reduction in bacteria numbers of 1.2 to 1.4 log CFU/g. The ascorbic acid content of the lettuce was not affected by these treatments. The combined treatment of hot water followed by ozonated water greatly inhibited PAL activity for up to 3 days of storage at 10 degrees C. Treatment with this combination greatly suppressed increases in the a* value. thus retarding the progress of browning compared with other treatments throughout the 6-day storage. NaOCI treatment also inhibited browning for up to 3 days of storage. Bacterial populations on the lettuce treated with sanitizers were initially reduced but then showed rapid growth compared with that of the water wash treatment, which did not reduce bacterial counts initially.
  • S Koseki, S Isobe
    INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY 104 3 239 - 248 2005年10月 [査読有り][通常論文]
     
    The growth of pathogenic bacteria Escherichia coli O157:H7, Salmonella spp., and Listeria monocytogenes on iceberg lettuce under constant and fluctuating temperatures was modelled in order to estimate the microbial safety of this vegetable during distribution from the farm to the table. Firstly, we examined pathogen growth on lettuce at constant temperatures, ranging from 5 to 25 degrees C, and then we obtained the growth kinetic parameters (lag time, maximum growth rate (mu max), and maximum population density (MPD)) using the Baranyi primary growth model. The parameters were similar to those predicted by the pathogen modelling program (PMP), with the exception of MPD. The MPD of each pathogen on lettuce was 2-4 log(10) CFU/g lower than that predicted by PMP. Furthermore, the MPD of pathogens decreased with decreasing temperature. The relationship between root mu(max). and temperature was linear in accordance with Ratkowsky secondary model as was the relationship between the MPD and temperature. Predictions of pathogen growth under fluctuating temperature used the Baranyi primary microbial growth model along with the Ratkowsky secondary model and MPD equation. The fluctuating temperature profile used in this study was the real temperature history measured during distribution from the field at harvesting to the retail store. Overall predictions for each pathogen agreed well with observed viable counts in most cases. The bias and root mean square error (RMSE) of the prediction were small. The prediction in which mu(max) was based on PMP showed a trend of overestimation relative to prediction based on lettuce. However, the prediction concerning E. coli O157:H7 and Salmonella spp. on lettuce greatly overestimated growth in the case of a temperature history starting relatively high, such as 25 degrees C for 5 h. In contrast, the overall prediction of L. monocytogenes under the same circumstances agreed with the observed data. (c) 2005 Elsevier B.V. All rights reserved.
  • S Koseki, S Isobe
    INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY 101 2 217 - 225 2005年05月 [査読有り][通常論文]
     
    The growth of pathogenic bacterium Listeria monocytogenes on fresh-cut iceberg lettuce under constant temperatures was modelled in order to investigate microbial safety during distribution of this vegetable. We examined the effects of several incubation temperatures, ranging from 5 to 25 degrees C, on bacterial growth. These data were fitted to the Baranyi model and the curves showed a high correlation coefficient at all temperature (R-2> 0. 95). In addition, the native bacterial flora of the lettuce did not affect the growth rate of.L monocylogenes regardless of incubation temperature. However, the lag time was reduced at a ratio of native bacteria to inoculated L. nionocytogenes (100: 1) at low incubation temperatures (5 and 10 degrees C). Furthermore, the maximum population density (MPD) was increased at a low ratio of native to inoculated L. monocytogenes (1: 1) at all incubation temperatures. These results were compared with the previous work published by Buchanan et al. (1989) [Buchanan, R.L., Stahl, H.G., Whiting, R.C., 1989. Effects and interactions of temperature, pfl, atmosphere, sodium chloride, and sodium nitrite on the growth of Listeria monocytogenes. J. Food Prot. 52, 844-85 1] that is being developed at the US Department of Agriculture (USDA) Agricultural Research Service's Pathogen Modelling Program (PMP). The broth-based Buchanan model for L. monocytogenes was found to markedly deviate from the observed data. In order to investigate this discrepancy, we examined the effects of medium environment and nutrient content on L. monocytogenes growth using tryptic soy agar plates (TSAP) and agar plates (AP) containing 1.7% sucrose. The inoculated bacteria on both TSAP and AP showed slower growth rates than that predicted by thc PMP. The MPD of bacteria grown on TSAP was similar to the PMP model (similar to 9 og(10) CFU/ml or plate (circle of diameter of 90 mm)) regardless of the incubation temperature. By contrast, the MPD observed on AP was similar to 4 log(10) CFU lower than that observed on TSAP or predicted by the PMP. Both the growth rate and the MPD of L. monocytogenes on AP were similar to those on lettuce. These results suggest that the solid medium and poor nutrient content inhibited the growth of L. monocytogenes on lettuce. The growth rates of the inoculated L. monocytogenes on all media were described using Ratkowsky's simple square root model. (c) 2005 Elsevier B.V. All rights reserved.
  • 吉田 恭一郎, 阿知波 信夫, 片寄 政彦, 木澤 由美子, 小関 成樹, 五十部 誠一郎, 阿部 一博
    日本食品科学工学会誌 : Nippon shokuhin kagaku kogaku kaishi = Journal of the Japanese Society for Food Science and Technology 52 6 266 - 272 Japanese Society for Food Science and Technology 2005年 [査読有り][通常論文]
     
    電解水の殺菌処理の高度化について検討した.(1) ネギの部位によって有効塩素の消失量に違いが認められた. 有効塩素濃度, 処理水量, 殺菌効果の関係や作業の簡便さを考慮し, 強酸性電解水による2分間浸漬が最適であると考えられた. 前処理として強アルカリ性電解水処理を行うことがネギでも有効であることが明らかとなった. その場合も, 温強アルカリ性電解水で1分以上の処理を行った後, 冷強酸性電解水で2分以上の攪拌を行う処理が最適であると考えられた.(2) 共焦点レーザー顕微鏡を用いてレタスの表面を観察した結果, 気孔周辺や細胞の境界部分など変化がある部分に多数の菌が存在していることが明らかとなった. そのため, 強酸性電解水で処理を行っても菌との接触が容易ではないために高い殺菌効果につながっていないと考えられた. ネギに関しても同様に, 表面の変化がある部分に多数の菌の付着が認められ, その分布もある程度の深度まで達していることが明らかとなった. またレタスと同様に, 気孔周辺に存在している菌や損傷細胞等の中へ侵入している菌に対する高い殺菌効果は得にくいと考えられた.
  • K Yoshida, N Achiwa, M Katayose, S Koseki, S Isobe, K Abe
    JOURNAL OF THE JAPANESE SOCIETY FOR FOOD SCIENCE AND TECHNOLOGY-NIPPON SHOKUHIN KAGAKU KOGAKU KAISHI 52 6 273 - 277 2005年 [査読有り][通常論文]
     
    Most cases of microbial food contamination may be caused by cross-contamination at food processing stage. In this study, application of electrolyzed water for pre-cut vegetables was examined for bacterial control at their processing stage. The authors previously reported basic research on enhanced bactericidal effect by electrolyzed water on pre-cut vegetables. Based on the previous report, this study aimed for advanced experiment considering actual field applications and for examination of the resulting effects. In addition to microbial food contamination, chemical contamination was also studied. The rinsing effect of electrolyzed water was examined for the put-pose of reducing residual pesticide used for cultivation. To establish an effectual washing process in actual applications, a washing tank was installed in a pre-cut vegetable processing plant, and routine bacterial counting was performed. As the result of preservation study on the green onion treated in the washing tank, 5 degrees C storage was more effective than room temperature or 20 degrees C storage in controlling bacterial growth. Before the washing tank was installed, bacteria attached to green onion varied to some degree but counted 10(5)-10(6)CFU/g for total bacteria and 10(1)-10(5) CFU/g for total coliforms. The washing tank treatment successfully reduced the bacterial count to 10(4)-10(6)CFU/g for total bacteria and negative- 10(4)CFU/g for total coliforms. A commercial pesticide was used to determine the effect of electrolyzed water in rinsing residual pesticide. Mixture with acidic electrolyzed water resulted in reducing detection of an organic phosphorus pesticide Phenthoate (TM). in a model experiment, a combined treatment with hot alkaline electrolyzed water and cold acidic electrolyzed water was most effective. The results suggested that electrolyzed water might be effective in rinsing residual pesticide.
  • S Koseki, S Isobe, K Itoh
    JOURNAL OF FOOD PROTECTION 67 11 2544 - 2549 2004年11月 [査読有り][通常論文]
     
    Acidic electrolyzed water (AcEW) was used as frozen AcEW (AcEW-ice) for inactivation of Listeria monocytogenes and Escherichia coli O157:H7 on lettuce. AcEW-ice was prepared from AcEW with 20,50, 100, and 200 ppm of available chlorine by freezing at -40degreesC and generated 30, 70, 150, and 240 ppm of chlorine gas (CIA respectively. The AcEW-ice was placed into styrene-foam containers with lettuce samples at 20degreesC for 24 h. Although AcEW-ice generating 30 ppm Cl(2) had no effect on L. monocytogenes cell counts, AcEW-ice generating 70 to 240 ppm of Cl(2) significantly (P < 0.05) reduced L. monocytogenes by ca. 1.5 log CFU/g. E coli O157:H7 cell counts were reduced by 1.0 log CFU/g with AcEW-ice generating 30 ppm of Cl(2). ACEW-ice generating 70 and 150 PPM of Cl(2) reduced E. coli O157:H7 by 2.0 log CFU/g. Further significant reduction of E. coli O157:H7 (2.5 log CFU/g) was demonstrated by treatment with AcEW-ice generating 240 PPM Of Cl(2). However, treatment with ACEW-ice generating 240 pprn of Cl(2) resulted in a physiological disorder resembling leaf burn. AcEW-ice that generated less than 150 PPM Of Cl(2) had no effect on the surface color of the lettuce. AcEW-ice, regardless of the concentration of the emission of Cl(2), had no effect on the ascorbic acid content in the lettuce. The weight ratio of lettuce to AcEW-ice required was determined to be over 1:10. The bactericidal effect of AcEW-ice appeared within the first 2 h. The use of AcEW-ice provides simultaneously for low temperature storage and inactivation of bacteria.
  • S Koseki, K Yoshida, Y Kamitani, S Isobe, K Itoh
    FOOD MICROBIOLOGY 21 5 559 - 566 2004年10月 [査読有り][通常論文]
     
    Cut lettuce dip-inoculated with Escherichia coli O157:H7 and Salmonella was treated with alkaline electrolyzed water (AIEW) at 20degreesC for 5 min, and subsequently washed with acidic electrolyzed water (AcEW) at 20degreesC for 5 min. Pre-treatment with AIEW resulted in an approximate 1.8 log(10) cfu/g reduction of microbial populations, which was significantly (p less than or equal to 0.05) greater than microbial reductions resulting from other pre-treatment solutions, including distilled water and AcEW. Repeated AcEW treatment did not show a significant bacterial reduction. Mildly heated (50degreesC) sanitizers were compared with normal (20degreesC) or chilled (4degreesC) sanitizers for their bactericidal effect. Mildly heated AcEW and chlorinated water (200 ppm free available chlorine) with a treatment period of 1 or 5 min produced equal reductions of pathogenic bacteria of 3 log(10) and 4 log(10) cfu/g, respectively. The procedure of treating with mildly heated AIEW for 5 min, and subsequent washing with chilled (4degreesC) AcEW for period of 1 or 5 min resulted in 3-4 log(10) cfu/g reductions of both the pathogenic bacterial counts on lettuce. Extending the mild heat pre-treatment time increased the bactericidal effect more than that observed from the subsequent washing time with chilled AcEW. The appearance of the mildly heated lettuce was not deteriorated after the treatment. In this study, we have illustrated the efficacious application of AIEW as a pre-wash agent. and the effective combined use of AIEW and AcEW. (C) 2003 Elsevier Ltd. All rights reserved.
  • S Koseki, K Yoshida, S Isobe, K Itoh
    JOURNAL OF FOOD PROTECTION 67 6 1247 - 1251 2004年06月 [査読有り][通常論文]
     
    An examination was made of the efficacy of acidic electrolyzed water (AcEW, 30 ppm free available chlorine), ozonated water (5 ppm ozone), and a sodium hypochlorite solution (NaOCl, 150 ppm free available chlorine) for use as potential sanitizers of cucumbers and strawberries. AcEW and NaOCl reduced the aerobic mesophiles naturally present on cucumbers within 10 min by 1.4 and 1.2 log CFU per cucumber, respectively. The reduction by ozonated water (0.7 log CFU per cucumber) was significantly less than that of AcEW or NaOCl (P less than or equal to 0.05). Cucumbers washed in alkaline electrolyzed water for 5 min and then treated with AcEW for 5 min showed a reduction in aerobic mesophiles that was at least 2 log CFU per cucumber greater than that of other treatments (P less than or equal to 0.05). This treatment was also effective in reducing levels of coliform bacteria and fungi associated with cucumbers. All treatments offered greater microbial reduction on the cucumber surface than in the cucumber homogenate. Aerobic mesophiles associated with strawberries were reduced by less than 1 log CFU per strawberry after each treatment. Coliform bacteria and fungi associated with strawberries were reduced by 1.0 to 1.5 log CFU per strawberry after each treatment. Microbial reduction was approximately 0.5 log CFU per strawberry greater on the strawberry surface than in the strawberry homogenate. However, neither treatment was able to completely inactivate or remove the microorganisms from the surface of the cucumber or strawberry.
  • S Koseki, K Yoshida, Y Kamitani, K Itoh
    JOURNAL OF FOOD PROTECTION 66 11 2010 - 2016 2003年11月 [査読有り][通常論文]
     
    The influence of bacterial inoculation methods on the efficacy of sanitizers against pathogens was examined. Dip and spot inoculation methods were employed in this study to evaluate the effectiveness of acidic electrolyzed water (AcEW) and chlorinated water (200 ppm free available chlorine) against Escherichia coli O157:H7 and Salmonella spp. Ten pieces of lettuce leaf (5 by 5 cm) were inoculated by each method then immersed in 1.5 liters of AcEW, chlorinated water, or sterile distilled water for 1 min with agitation (150 rpm) at room temperature. The outer (abaxial) and inner (adaxial) surfaces of the lettuce leaf were distinguished in the spot inoculation. Initial inoculated pathogen population was in the range 7.3 to 7.8 log CFU/g. Treatment with AcEW and chlorinated water resulted in a 1 log CFU/g or less reduction of E. coli O157:H7 and Salmonella populations inoculated with the dip method. Spot inoculation of the inner surface of the lettuce leaf with AcEW and chlorinated water reduced the number of E. coli O157:H7 and Salmonella by approximately 2.7 and 2.5 log CFU/g, respectively. Spot inoculation of the outer surface of the lettuce leaf with both sanitizers resulted in approximately 4.6 and 4.4 log CFU/g reductions of E. coli O157:H7 and Salmonella, respectively. The influence of inoculation population size was also examined. Each sanitizer could not completely eliminate the pathogens when E. coli O157:H7 and Salmonella cells inoculated on the lettuce were of low population size (10(3) to 10(4) CFU/g), regardless of the inoculation technique.
  • S Koseki, K Itoh
    JOURNAL OF FOOD PROTECTION 65 2 326 - 332 2002年02月 [査読有り][通常論文]
     
    Nitrogen (N-2) gas packaging for fresh-cut vegetables (lettuce and cabbage) has been examined as a means of modified atmosphere packaging (MAP) for extending the shelf life of cut vegetables. Gas composition in enclosed packages that contained cut vegetables and were filled with 100% N-2 had an oxygen (O-2) concentration of 1.2 to 5.0% and a carbon dioxide (CO2) concentration of 0.5 to 3.5% after 5 days of storage. An atmosphere of low concentrations of O-2 and high CO2 conditions occurred naturally in the package filled with N-2 gas. Degradation of cut vegetables in terms of appearance was delayed by N-2 gas packaging. Because of this effect, the appearance of fresh-cut vegetables packaged with N-2 gas remained acceptable at temperatures below 5degreesC after 5 days. Treatment with acidic electrolyzed water (AcEW) contributed to the acceptability of the vegetables' appearance at 5 and 10degreesC in the air-packaging system. N-2 gas packaging did not significantly affect the growth of microbial populations (total aerobic bacteria, coliform. bacteria, Bacillus cereus, and psychrotrophic bacteria) in or on cut vegetables at 1, 5, and 10degreesC for 5 days. Microbial growth in or on the cut vegetables was inhibited at 1degreesC for 5 days regardless of atmospheric conditions.
  • S Koseki, K Fujiwara, K Itoh
    JOURNAL OF FOOD PROTECTION 65 2 411 - 414 2002年02月 [査読有り][通常論文]
     
    We investigated the effects of frozen acidic electrolyzed water (AcEW) on lettuce during storage in a styrene-foam container. The lettuce was kept at 2 to 3degreesC for 24 h. Populations of aerobic bacteria associated with lettuce packed in frozen AcEW were reduced by 1.5 log CFU/g after storage for 24 h. With frozen tap water, no microorganism populations tested in this study were reduced. A frozen mixture of AcEW and alkaline electrolyzed water (A1EW) also failed to reduce populations of microorganisms associated with lettuce. Although chlorine gas was produced by frozen AcEW, it was not produced by the AcEW-A1EW mixture. This result indicates that the main factor in the decontandnative effect of frozen AcEW was the production of chlorine gas. Accordingly, low-temperature storage and decontamination could be achieved simultaneously with frozen AcEW during distribution.
  • S Koseki, K Itoh
    JOURNAL OF FOOD PROTECTION 64 12 1935 - 1942 2001年12月 [査読有り][通常論文]
     
    Effects of storage temperature (1, 5, and 10 degreesC) on growth of microbial populations (total aerobic bacteria, coliform bacteria, Bacillus cereus, and psychrotrophic bacteria) on acidic electrolyzed water (AcEW)-treated fresh-cut lettuce and cabbage were determined. A modified Gompertz function was used to describe the kinetics of microbial growth. Growth data were analyzed using regression analysis to generate "best-fit" modified Gompertz equations, which were subsequently used to calculate lag time, exponential growth rate, and generation time. The data indicated that the growth kinetics of each bacterium were dependent on storage temperature, except at 1 degreesC storage. At 1 degreesC storage, no increases were observed in bacterial populations. Treatment of vegetables with AcEW produced a decrease in initial microbial populations. However, subsequent growth rates were higher than on nontreated vegetables. The recovery time required by the reduced microbial population to reach the initial (treated with tap water [TW]) population was also determined in this study, with the recovery time of the microbial population at 10 degreesC being <3 days. The benefits of reducing the initial microbial populations on fresh-cut vegetables were greatly affected by storage temperature. Results from this study could be used to predict microbial quality of fresh-cut lettuce and cabbage throughout their distribution.
  • S Koseki, K Yoshida, S Isobe, K Itoh
    JOURNAL OF FOOD PROTECTION 64 5 652 - 658 2001年05月 [査読有り][通常論文]
     
    The disinfectant effect of acidic electrolyzed water (AcEW), ozonated water, and sodium hypochlorite (NaOCl) solution on lettuce was examined. AcEW (pH 2.6; oxidation reduction potential, 1140 mV; 30 ppm of available chlorine) and NaOCl solution (150 ppm of available chlorine) reduced viable aerobes in lettuce by 2 log CFU/g within 10 min. For lettuce washed in alkaline electrolyzed water (AlEW) for 1 min and then disinfected in AcEW for 1 min, viable aerobes were reduced by 2 log CFU/g. On the other hand, ozonated water containing 5 ppm of ozone reduced viable aerobes in lettuce 1.5 log CFU/g within 10 min. It was discovered that AcEW showed a higher disinfectant effect than did ozonated water significantly at P < 0.05. It was confirmed by swabbing test that AcEW, ozonated water, and NaOCl solution removed aerobic bacteria, coliform bacteria, molds, and yeasts on the surface of lettuce. Therefore, residual microorganisms after the decontamination of lettuce were either in the inside of the cellular tissue, such as the stomata, or making biofilm on the surface of lettuce. Biofilms were observed by a scanning electron microscope on the surface of the lettuce treated with AcEW. Moreover, it was shown that the spores of bacteria on the surface were not removed by any treatment in this study. However, it was also observed that the surface structure of lettuce was nor damaged by any treatment in this study. Thus, the use of AcEW for decontamination of fresh lettuce was suggested to be an effective means of controlling microorganisms.
  • S Koseki, K Itoh
    JOURNAL OF THE JAPANESE SOCIETY FOR FOOD SCIENCE AND TECHNOLOGY-NIPPON SHOKUHIN KAGAKU KOGAKU KAISHI 48 5 365 - 369 2001年 [査読有り][通常論文]
     
    We examined the effect of acidic electrolyzed water (AcEW), NaOCl solution (150 ppm), and tap water on the quality of fresh cut vegetables. The vegetable quality tested in this study was the color tone of the appearance, the total chlorophyll content, the beta -carotene content, and the ascorbic acid content. The appearance of the cut or non-cut vegetable was not changed by the 10 min soaking in AcEW. The total chlorophyll content in the cut cabbage and the cut lettuce soaked in AcEW for 10 min was decreased by 10 -20%. The beta -carotene content in the carrot soaked in AcEW for 10 min was decreased by about 30%. However, the reaction mechanism of these decreasing of pigment content is not clear. On the other hand, the ascorbic acid content in the cut cabbage, cut lettuce and cut cucumber treated with AcEW for 10 min was decreased by 20%, 15% and 35%, respectively. These results were also shown in the treatment with NaOCl solution and tap water. Thus, the loss in quality of the cut vegetable treated with AcEW was equivalent with NaOCl and tap water. Therefore, it was found out that AcEW did not affect the quality of cut vegetables.
  • S Koseki, K Itoh
    JOURNAL OF THE JAPANESE SOCIETY FOR FOOD SCIENCE AND TECHNOLOGY-NIPPON SHOKUHIN KAGAKU KOGAKU KAISHI 47 12 914 - 918 2000年 [査読有り][通常論文]
     
    It has been shown that acidic electrolyzed water was effective in the surface disinfection of shredded vegetables. In the treatment shredded vegetables were simply soaked in acidic electrolyzed water so far. In this research, in the disinfection of shredded vegetables by acidic electrolyzed water, the effectiveness of physical supplementary means used together was examined, Combined use of the physical supplementary means and acidic electrolyzed water did not contribute to disinfection. However, the physical supplementary means was shown to be considerably effective when vegetables were washed with alkaline electrolyzed water by physical supplementary means and then disinfected in acidic electrolyzed water by the physical supplementary means. This effect: was remarkable on cucumbers, but little on lettuces and cabbages. Stirring was most effective among the supplementary means used. It was found out that five minutes each of washing and disinfecting was necessary for high disinfectant effect on cucumbers. Moreover, it was suggested that: the effect of stirring was more effective than that of pretreatment of alkaline electrolyzed water on cucumber disinfection.
  • S Koseki, K Itoh
    JOURNAL OF THE JAPANESE SOCIETY FOR FOOD SCIENCE AND TECHNOLOGY-NIPPON SHOKUHIN KAGAKU KOGAKU KAISHI 47 12 907 - 913 2000年 [査読有り][通常論文]
     
    Electrolysis of dilute sodium chloride solution produces alkaline electrolyzed water (AlEW) in the cathode side, simultaneously produces acidic electrolyzed water (AcEW) in the anode side. AlEW presents high pH (above 11) and extremely low ORP (below -800 mV). There has been no study attempting to use AlEW for washing shredded vegetables. Thus we examined the availability of AlEW as wash water before disinfecting shredded vegetables (cabbages, lettuces, and cucumbers) with AcEW. Washing shredded vegetables by AlEW for one minute before disinfecting with AcEW was more effective than only disinfecting with AcEW for five minutes. Equally good results were ascertained among three different vegetables. Moreover, the activity of AcEW thigh ORP and available chlorine concentration) was little declined when prewashing with any solutions (AlEW, 17 mM NaOH, and tap water) was applied before disinfecting Although this effect was induced by not only AlEW but also tap water and 17 mM NaOH, in view of the disinfectant effect, it is suggested that washing with AlEW before disinfecting would be suitable for shredded vegetables as an effective utilization of AlEW.
  • S Koseki, K Itoh
    JOURNAL OF THE JAPANESE SOCIETY FOR FOOD SCIENCE AND TECHNOLOGY-NIPPON SHOKUHIN KAGAKU KOGAKU KAISHI 47 9 722 - 726 2000年 [査読有り][通常論文]
     
    Acidic electrolyzed water (AcEW) is a new disinfectant prepared by electrolyzing dilute sodium chloride solutions. AcEW has a low pH (below 2.7), high oxidizing reduction potential (ORP above+ 1 100 mV) and available chlorine concentration (ACC, 40 similar to 50 ppm). We studied the disinfectant effect of AcEW on five kinds of shredded vegetables. The microbial counts in lettuces, cabbages, carrots and burdocks were reduced from 1:10 to 1/100 of the initial numbers within 10 minuets by soaking the vegetables in AcEW. However, 20 minuets of soaking in AcEW were required for the initial microbial counts in cucumbers to be reduced by 1/10. The appearance of the vegetables did not deteriorate alter soaking for 20 minuets in AcEW. The disinfectant effect was not enhanced by prolongation of treatment time. Therefore, soaking shredded vegetables in AcEW for 10 similar to 20 minuets is sufficient to disinfect microbes contaminating the surface of the vegetables. Moreover, we compared the disinfectant effects of AcEW and sodium hypochlorite (ACC of about 150 ppm) on shredded lettuces, cabbages, cucumbers, carrots and burdocks. It was found that the disinfectant effect of AcEW was equivalent to that of sodium hypochlorite solution. Unlike sodium hypochlorite solution, which has been used as a disinfectant for shredded vegetables, AcEW is easy to handle and there is little residual chlorine odor. AcEW is therefore a useful substitute for sodium hypochlorite to disinfect shredded vegetables.
  • S Koseki, K Itoh
    JOURNAL OF THE JAPANESE SOCIETY FOR FOOD SCIENCE AND TECHNOLOGY-NIPPON SHOKUHIN KAGAKU KOGAKU KAISHI 47 12 888 - 898 2000年 [査読有り][通常論文]
     
    The main factor contributing to the disinfecting potential of acidic electrolyzed water (AcEW) is deduced to be the oxidizing power of available chlorine. In this study, we compared the reliability of two different methods for measuring the available chlorine concentration (ACC). Several AcEW solutions with different levels of ACC to which various reducing agents (ascorbic acid, ammonium iron (II) sulfate, and iron (II) chloride) had been added were prepared. These ACC levels were quantified by iodometry and the DPD (N, N-diethyl-p-phenylenediamine) method. In the case of AcEW with iron (II) ions, iodometry did not show the correct ACC. On the other hand, the DPD method correctly quantified ACC even in the case of AcEW with iron (II) ions. Thus, the DPD method is an appropriate method for measuring ACC in AcEW. Moreover, we investigated the effect of the available chlorine concentration (ACC) in AcEW on its disinfecting potential. First, we examined the disinfectant effects of AcEW on shredded vegetables. We found that there was no difference in the disinfectant effects between AcEW with high ACC (40 ppm) and low ACC (0.4 ppm). The similar effect was detected in AcEW with 0 ppm of ACC, a solution that seemed to be the same as hydrochloric acid. Moreover, tap water with pH adjusted to 2.4 showed the same disinfectant effect as that of AcEW. These results indicated that AcEW is a solution in which available chlorine is activated in a low pH condition. Next, we examined the disinfectant effects of AcEW on a suspension obtained from shredded vegetables in vitro. The disinfecting potential became weaker, but did not completely disappear, when ACC was reduced to 0 ppm, Thus, AcEW with low ACC could be used to disinfect shredded vegetables, although the disinfecting potential of AcEW would become weak. When the effective concentration of Acc was examined, it was found that the AcEW with ACC of less than 20 ppm did not have sufficient disinfectant potential. Moreover, it was found that high ORP (above 1000 mV) does not contribute to disinfecting potential. Thus, the lower limit of ACC in AcEW for AcEW to exert a sufficient disinfectant effect will be 20 ppm.
  • S Koseki, K Itoh
    JOURNAL OF THE JAPANESE SOCIETY FOR FOOD SCIENCE AND TECHNOLOGY-NIPPON SHOKUHIN KAGAKU KOGAKU KAISHI 47 5 390 - 393 2000年 [査読有り][通常論文]
     
    Electrolyzed Water (Acidic Electrolyzed Water, Alkaline Electrolyzed Water) has recently attracted the interest of researchers in various fields such as medicine, agriculture and food processing. in this study, we investigated the preservability of Electrolyzed Water produced in a two-cell batch-type apparatus. It was found that Acidic Electrolyzed Water could be preserved for one year under shaded and sealed conditions. However, Acidic Electrolyzed Water became inert after three days when exposed to light, although pH remained stable for one year. It was found out that the quality of Alkaline Electrolyzed Water changes easily regardless of preservation conditions.
  • Masuda, T., Koseki, S. Y., Yasumoto, K., Kitabatake, N.
    Journal of Agricultural and Food Chemistry 48 7 2000年

MISC

所属学協会

  • Editorial board member, Applied and Environmental Microbiology   Editorial board member, International Journal of Food Microbiology   Editorial board member, Journal of Food Protection   

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2021年04月 -2024年03月 
    代表者 : 小関 成樹
     
    乾燥食品（環境）において微生物が長期間にわたり生残するための乾燥ストレス耐性を獲得するメカニズムを，微生物細胞のガラス転移現象に焦点を絞り，その物理的状態の変化の観点から明らかにする。食中毒細菌の制御から有用細菌の安定保存までを可能とする科学的な基盤を構築することを目的とする。具体的には以下の3つの研究課題について取り組む。 初年度は、研究対象を従来の細菌だけから，真菌類（カビ，酵母）や細菌芽胞に拡大して，ガラス転移温度（Tg）と水分活性（aw）との関係を昇温レオロジー測定によって明らかにした。また，得られたTgと保存中の生残に及ぼす影響を明らかにする。具体的には乾燥食品の食中毒原因として主要なサルモネラ属菌およびその近縁種の代替細菌としてCronobacter sakazakii など様々な食品の腐敗および変敗の原因となる細菌芽胞について検討した。 また、乾燥耐性が高く，食品産業において重要な細菌 Cronobacter sakazakiiと酵母を用いて、様々なawに調節した試料の分子ダイナミクス（mean square displacement, MSD）を幅広い温度範囲で測定した。また，研究室既設の温度変調FT-IRを用い，各試料の分子間相互作用変化をガラス転移と水和レベルの観点から検討した。さらに、従来よりも高感度かつ広い温度範囲で微生物のガラス転移を検出可能な方法として，直列型昇温レオロジー測定を構築した。モデル試料としてアルブミンを用い，装置の効果を検証した。
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2018年04月 -2021年03月 
    代表者 : 小関 成樹, 川井 清司
     
    本年度は以下について検討した。 1.細菌のガラス転移温度(Tg)と水分活性(aw)との関係解明 ガラス転移に伴う力学的性質の変化を簡便に捉えるための方法として，市販のレオメータに温度制御装置を取り付けた昇温レオロジー測定法を 構築し，この測定手法を乾燥状態の細菌に適用することを考案し，昨年度の検討を通じてサルモネラの細菌細胞のガラス転移温度(Tg)も昇温 レオロジー測定によって検出し得ることを確認した。今年度は，試料調製や測定条件等を慎重に検討した上で，サルモネラ以外のクロノバクタ ー属菌等の乾燥に耐性を有する菌種におけるTgと水分活性(aw)の関係の違いを検討した。さらに，ガラス転移温度をパラメータに組み込んだ ，細菌の生残予測モデルを開発した。 2.微生物のガラス転移温度(Tg)制御方法の開発 細菌のTgを可塑剤や硬化剤などによって制御する場合，それらの物質が細菌の細胞膜を透過する必要がある。一般に可塑剤は低分子であるた め，電解質やポリオール溶液に浸すことで，容易に成し得られる。問題は細胞内への硬化剤の導入である。一般にTgの高い成分は分子サイズも 大きく，細胞膜を透過させることはできない。この問題を克服するにあたり，申請者らは低分子同士の複合体形成に着目している。既往の研究 (Macfarlane et al., 2002)により，ある種の電解質(塩化マグネシウム等)とポリオール(グリセロール等)とは乾燥状態において複合体 を形成し，Tgが相乗的に高くなることが知られている。これらの物質はいずれも細胞膜を透過可能な分子サイズであり，細胞毒性も低い。本年 度は細胞内に導入した後，乾燥することで，細胞内部で複合体が形成され，内部のTgを引き上げることが可能かを詳細に検討した。
  • 食物消化過程におけるカンピロバクターの生残特性を基盤とする新たな用量反応モデルの開発
    内閣府：食品健康影響評価技術研究
    研究期間 : 2018年 -2019年 
    代表者 : 小関成樹
  • 日本学術振興会：科学研究費助成事業 国際共同研究加速基金(国際共同研究強化)
    研究期間 : 2016年 -2018年 
    代表者 : 小関 成樹
     
    本研究ではD-Trpにより細菌の増殖が抑制されるメカニズムを解明するためD-Trpが細菌細胞内で作用している可能性，細菌細胞外で作用している可能性の2つの仮説を立て検証を行った。得られた結果を総合的に判断すると，D-Trpによる細菌の増殖抑制はD-Trpが細菌に取り込まれて起こるのでなく，細胞膜や細胞外部で作用している可能性が高いという結論が得られた。またD-Trpにより増殖抑制されたE. coliは増殖可能な環境下に移ると再増殖したことから，D-Trpを微生物制御に利用する際は常に環境中にD-Trpが存在する必要があると考えられる。
  • 必須アミノ酸による食品有害細菌の増殖抑制効果：作用機構の解明と予測モデルの開発
    文部科学省：科学研究費助成事業 国際共同研究加速基金（国際共同研究強化）
    研究期間 : 2015年 -2018年 
    代表者 : 小関成樹
  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    研究期間 : 2014年04月 -2017年03月 
    代表者 : 小関 成樹
     
    新たな微生物制御技術の開発を最終的な目的とし，D-トリプトファンによるE. coliの増殖抑制効果に関する基礎的な検討を行った結果，以下の3点を明らかにした。1）D-トリプトファンによるE. coliの増殖抑制効果は浸透圧ストレスのみによって誘導されるものでなく，NaCl濃度が重要な役割を果たしている。2）NaCl濃度，D-トリプトファン濃度を説明変数とする，E. coli増殖限界予測モデルを構築し，効果発現に必要な濃度条件の組み合わせを探索可能とした。3）D-トリプトファンの取り込みによってE. coliは死滅し，その死滅速度は温度依存性が明確で，増殖の至適温度付近で最大の死滅速度になる。
  • 損傷菌の発生機序の解明と検出・制御技術の開発
    農林水産省：食品の安全性と動物衛生の向上のためのプロジェクト
    研究期間 : 2013年 -2017年 
    代表者 : 稲津康弘
  • 日本学術振興会：科学研究費助成事業 若手研究(B)
    研究期間 : 2011年04月 -2015年03月 
    代表者 : 小関 成樹
     
    細菌のストレス応答時の適合溶質の細胞質内への取り込みに注目して，細菌が誤って適合溶質として機能しない非適合溶質を取り込むことによって，代謝阻害を誘導し，結果として増殖を抑制する，との仮説のもとに種々のアミノ酸をはじめとする食品素材の細菌増殖抑制効果を明らかにした。アミノ酸のなかでも，D-トリプトファンが顕著な効果を示すことを明らかにするとともに，最適な作用条件を解明した。新たな非熱的な微生物制御手法として利用が期待できる。
  • 低水分含量食品中における食中毒細菌（サルモネラ、腸管出血性大腸菌）の菌数変動および生存確率予測モデルの開発
    内閣府：食品健康影響評価技術研究
    研究期間 : 2014年 -2015年 
    代表者 : 小関成樹
  • 日本学術振興会：科学研究費助成事業 若手研究(A)
    研究期間 : 2009年 -2012年 
    代表者 : 小関 成樹
     
    近年,食品の安全性を確保する手法として,「リスク」の概念の導入が進みつつある。リスク概念から生まれた新たな概念として,フードチェーン全体を考慮するFood Safety Objective(FSO)が提案されている。本研究ではFSOに対応可能な新たな殺菌評価手法を開発することを目的として,殺菌効果の評価を従来の速度論的な評価から,確率論的な評価へ転換する。さらに,確率論的な評価の中で、殺菌処理によりネガティブな効果を受ける品質の評価を取り入れて,品質面と殺菌効果との最適化を図るための新たな概念として,安全性をゾーンとして捉えるStatistical Safety Zone(SSZ,確率論的安全ゾーン)理論を提案する。本年度は加熱殺菌の指標菌としてC.sporogens, B.subtilisおよびB.coagulansについて検討した。加熱温度,加熱時間,pH,水分活性といった基本要因が殺菌効果に及ぼす影響を明らかにして,新たな確率論的な殺菌予測モデルを開発するための基礎データを蓄積した。取得データは死滅確率(殺菌成功)をロジスティック回帰分析によって,多数の要因を組み込んで記述する数理モデルへと発展させることを可能とする。さらに、本年度は導入したレトルト殺菌機を用いて加熱方式の違いによる殺菌効果の違いについても明らかにして、それらの差異を従来殺菌の指標として用いられてきたF値による評価との関係を明らかにして、新たな評価手法開発の基盤を構築した。
  • 予測微生物学的解析手法を用いた微生物学的リスク評価システムの開発
    内閣府：食品健康影響評価技術研究
    研究期間 : 2007年 -2009年 
    代表者 : 小関成樹
  • 養液栽培におけるオゾン水による微生物制御と生産安定技術の開発
    農林水産省：先端技術を活用した農林水産研究高度化事業
    研究期間 : 2007年 -2008年 
    代表者 : 谷岡 隆
  • 日本学術振興会：科学研究費助成事業 若手研究(B)
    研究期間 : 2006年 -2008年 
    代表者 : 小関 成樹
     
    非熱処理の一つである高圧処理における殺菌効果に及ぼす種々の環境要因を定量的に評価して,従来の死滅曲線を求めるモデル化手法とは異なる殺菌効果予測モデルを実際の食品系において開発した。また,高圧処理によって生ずる損傷菌の回復を制御するために,高圧処理後に温和な加熱処理を施す手法を開発した。さらに,損傷回復制御条件の最適化のための数理モデルを開発し,必要に応じた処理条件の選定を可能とした。
  • 日本学術振興会：科学研究費助成事業 特別研究員奨励費
    研究期間 : 2003年 -2004年 
    代表者 : 小関 成樹
     
    本研究は希薄な食塩水を電気分解することによって得られる強酸性電解水の殺菌力と,青果物の微生物増殖過程とに注目して,以下の3点を目的としている. 1)強酸性電解水の殺菌効果を,青果物に接種した食中毒細菌に対する微生物学的な試験と共焦点レーザー蛍光顕微鏡(CLSM)による視覚化によって検討し,強酸性電解水の青果物における作用機構を明らかにする. 2)強酸性電解水の新たな利用方法として,電解水氷の有効な活用方法を開発する.そのために,電解水氷の殺菌特性および冷却特性を明らかにする. 3)強酸性電解水あるいは電解水氷によって殺菌した青果物の安全性を確保しつつ流通させるために,予測微生物学の手法を用いて,青果物の保存中における食中毒細菌増殖予測モデルを開発する. の以上3項目であるが,本年度はE.coli O157:H7をはじめとする種々の食中毒細菌青果物に接種し,青果物上での食中毒菌の増殖特性について検討した.一定温度条件下における増殖についての予測モデルの開発をした.さらに,変動温度条件にも対応できる予測モデルを開発して,実際の流通中の温度履歴からレタス上の食中毒細菌の増殖を精度良く予測することができた.この成果によって,温度履歴を測定することでその野菜における微生物学的な安全性を推定,評価することが可能になった.これらの結果はInternational Journal of Food Microbiologyに2報投稿し,受理され現在印刷中である. 以上のように,本年度の研究実施状況は当初の計画通りに順調に進捗した.

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