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京都大学 / 新制・課程博士 / 博士(農学) / 甲第24661号 / 農博第2544号 / 新制||農||1098(附属図書館) / 学位論文||R5||N5442(農学部図書室) / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 矢野 浩之, 教授 和田 昌久, 教授 今井 友也 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

M.S.

Seafood products are a common consumer choice and a variety of cooking methods are used in seafood preparation. Although often cooked, products such as shrimp and salmon remain some of the most common carriers of foodborne disease. Cooking these products at elevated temperatures efficiently reduces foodborne disease causing pathogens to a safe level, but applying too much heat to seafood products can produce an overcooked, low quality food. It is necessary to investigate the cooking processes used in seafood preparation and establish appropriate consumer cooking parameters that optimize both the quality and microbial safety of the products. To achieve these goals, this study develops mathematical models for the inactivation of Salmonella sp., change in quality attributes, and the product heating profiles during the cooking process for shrimp and Atlantic salmon. Studies were performed to monitor the product heating profile during the baking and boiling of shrimp and the baking and pan-frying of salmon. Product color, texture, moisture content, mass loss, and pressed juice were evaluated during the cooking processes as the products reached the internal temperature recommended by the FDA. Studies were also performed on the inactivation of Salmonella cocktails in homogenized and non-homogenized shrimp and salmon. To effectively predict inactivation during cooking, the Bigelow, Fermi distribution, and Weibull distribution models were applied to the homogenized data. Minimum cooking temperatures necessary to destroy Salmonella sp. in shrimp and salmon were also determined. The heating profiles of the two products were modeled using the finite difference method. Temperature data directly from the modeled heating profiles was then used in the kinetic modeling of quality change and Salmonella inactivation during cooking. It was concluded that consumers need to judge the doneness of both shrimp and Atlantic salmon by the lightness factor (CIE L*) of the core region of both products. The core region's lightness factor, which a consumer may consider as opaqueness, more accurately represented the thermal doneness than the external qualities. The FDA's current recommendations for a 3 log reduction for intact seafood products and homogenized seafood products were each analyzed. Results were in agreement with the recommended 68°C plus 15 seconds for homogenized products. For intact products, shrimp inactivation results were in agreement with the recommended 63°C plus 15 seconds, but intact salmon achieved only a 2 log reduction by the temperature-time combination. It was also found that predictive models can effectively describe the survival data for two Salmonella cocktails. The Weibull distribution model, which takes into account any tailing effect in survival data, fit the survival data of Salmonella in shrimp acceptably. The Fermi distribution model, which incorporates any shouldering effect in data, was an acceptable fit for the inactivation data for salmon. Using three-dimensional slab geometry for salmon fillets and two-dimensional frustum cone geometry for shrimp resulted in acceptable model predictions of thermal distributions for the cooking methods studied. The temperature data attained directly from the modeled heating profiles was effectively used in the predictive quality and inactivation models. Agreeable first-order kinetic models were formulated for Î L and Î C color parameters in shrimp and salmon. Other kinetic models formulated were for texture change in salmon and pressed juice in both salmon and shrimp. Using a fixed inactivation level of 3 logs and a fixed quality of 95% best quality, optimal cooking conditions were determined that both provide a high quality product and assure microbial safety. Based on the specific cooking methods in this study, the optimal boiling times for extra jumbo and colossal sized shrimp were 100 seconds and 159 seconds, respectfully. The optimal oven baking times were 233 seconds for extra jumbo shrimp and 378 seconds for colossal shrimp. For Atlantic salmon, the optimal oven baking time was 1132 seconds and the optimal pan frying time was 399 seconds. / Master of Science

Microwave Blanching instructions for a variety of vegetables have recently been published by several sources. More research is needed, however, to establish microwave blanching times that are sufficient to destroy enzymes which cause nutritional and sensory deterioration in frozen vegetables while maintaining optimal quality. In the present study the General Electric Company's recommended blanch times for carrots and green beans were investigated using three microwave ovens. Peroxidase was used as an indicator enzyme for measuring blanching adequacy. It was determined that oven variation had no significant effect on percent residual peroxidase activity in either vegetable (p > 0.05). A large degree of standard deviation in the percent residual peroxidase activity was found among the blanched portions of vegetable. This variation was attributed to the inconsistent levels of peroxidase enzyme in the vegetables themselves. Blanch time had the most significant impact on percent residual peroxidase activity (p < 0.01). After a four-minute blanch, carrots retained approximately 21-25% peroxidase activity and green beans retained approximately 37-46% peroxidase activity. These ranges are much higher than the acceptable level of 5% residual peroxidase activity. Six minutes of blanching for green beans and five minutes of blanching for carrots were required to reduce residual peroxidase activity to acceptable levels. Vegetables with such low peroxidase activity show no deleterious enzyme related changes during frozen storage. Microwave blanching has the potential to be an acceptable alternative to hot water blanching, but further research is needed to optimize microwave blanching procedures. / Master of Science

This study was conducted to determine the effect of heating methods (conventional and microwave), heating temperatures, and refrigerated storage on the flavor deterioration in precooked chicken parts. Chicken breasts and legs were evaluated by chemical analyses and sensory evaluation. Data was analyzed by Fisher's least significant difference (LSD) and Duncan's test. Results of the thiobarbituric acid test (TBA) indicated that heating temperature, regardless of heating method had a significant influence on oxidative deterioration. When the legs were heated for a longer time at a lower temperature, the TBA values significantly increased indicating heightened warmed-over flavor (WOF). Two-day refrigerated storage had no measurable influence on the TBA numbers. The legs generally had a higher degree of lipid oxidation reflected by higher TBA values. Heating method and 2-day refrigerated storage did not have a significant effect on the nonheme iron content of breasts or legs. The effects of heating temperature were inconsistent for the legs and breasts which was attributed to the different initial iron content of the legs, and the release of nonheme iron during the initial processing of the legs. The nonheme iron values of the legs were greater relative to the breasts. Heating and storage in general increased the area of peak 3 in legs, but had no effect on the breasts. A significant increase in the hexanal (peak 8) content of legs occurred upon 2-day storage, but not for breasts. Peak 7 significantly decreased when the breasts were heated, stored, and reheated. This was not the case for the legs. Sensory panelists could not differentiate between heating methods or temperatures for either part. / Master of Science

Microwaves heat food rapidly and foods are prepared in less time. However, due to non-uniform heating nature of microwave cooking, there exists a serious concern over complete elimination of pathogens in the food. There has been an increase in interest to accurately understand the behavior of different food materials in a microwave field and microbial inactivation during microwave cooking. Recent research showed that fat content in muscle food plays an important role in microbial inactivation by increasing the inactivation level with an increase in the fat level. It was also demonstrated that muscle food heats up differently than a vegetable food product. Cooking food in a microwave oven either by covering the food container or not results in significantly different temperature profiles. The current research attempts to use modeling techniques to analyze impact of these factors on microwave heating. Mathematical modeling is faster, easier and economically better than actual experiments in determining heating behavior of a microwave-cooked food. Though modeling cannot completely replace actual experiments, it can be used as a tool to understand the effects of various factors influencing the microwave cooking. A factor that is highly important during microwave processing is dielectric properties of the material. The interaction of microwave with the food is mainly based on its dielectric properties, which can change with temperature. Therefore, determination of dielectric properties of food with respect to temperature becomes critical. The current research project has two parts. One to determine the dielectric properties of food being tested and another is to employ mathematical modeling techniques to analyze the effect of fat content, food type and the effect of cooking food by covering the bowl using the lid and not covering bowl. Dielectric properties of ground beef patties at 4%, 9%, 20% fat levels and frozen broccoli were determined using an open-ended, 3.6 mm diameter, semi-rigid coaxial line with copper conductors, connected to a network analyzer. The properties were determined at various temperatures. Foods were measured in triplicate. Results showed that dielectric constant and dielectric loss factor of low fat ground beef were higher than that of high fat level ground beef. In addition, the dielectric properties of florets were lower than that of stem parts for frozen broccoli. A 1,200W, household type microwave oven was used in this study to heat the food. Food was placed in a microwave-safe glass bowl and cooked for 120 seconds. One headspace and three internal temperature measurements were recorded for every 0.6 seconds. Five replications were performed. Finite element method was used as modeling technique and temperatures were predicted. Experimental and predicted temperature values were compared. Results showed that the model used in the study was more suitable for modeling the uncovered cooking than covered cooking process. Modeling results also revealed that high fat ground beef patties reached higher temperature than low fat patties. In high fat meat products, fat content also contributed to increase in temperature during microwave heating. In vegetable products and low fat meat food, moisture content is mainly responsible for microwave heating. A more extensive study on critical fat level above which fat content helps in increasing temperature is needed. In addition, inclusion of steam properties in the headspace for modeling the covered cooking is recommended. / Master of Science

Use of the bioluminometric ATP assay was evaluated for estimating total bacterial counts in ground beef. Minimum sensitivity was found to be 10⁶ cfu/g using a double filtration procedure for sample preparation. Although ATP content per cfu decreased approximately 10 fold during storage, correlation of total aerobic plate count (APC) with microbial ATP content was 0.96. Selective non-microbial ATP extraction with ATPase treatment was evaluated for use in conjunction with the double filtration procedure to increase assay sensitivity. The new method was effective for removing additional non-microbial ATP without reducing ATP in bacteria. Estimated APC values were generally accurate to within ±0.50 log for ground beef samples above the detection limit of 5 x 10⁴ cfu/g. ATPase treatment increased sensitivity of the ATP assay and APC estimation by about 1 log while increasing assay time by 40 minutes, for a total of 60 minutes for 4 samples assayed in triplicate. The ATP assay was evaluated for use with ground beef patties inoculated with mixed ground beef spoilage flora, <i>Pseudomonas</i>, or <i>Lactobacillus</i> and stored at 2°C or 10°C using oxygen permeable or impermeable (vacuum) packaging. Excellent correlation (r²=0.95) was obtained for each inoculum and storage condition over the range of 5 x 10⁴ to 1 x 10⁹ cfu/g, when estimated APC values were compared with experimentally observed APC values. Usefulness of the ATP assay for estimating APC values of frozen ground beef was evaluated. Retail ground beef and <i>Lactobacillus</i>- and <i>Pseudomonas</i>-inoculated beef were frozen and thawed at different rates and examined for APC and microbial ATP content. Results indicated that, although freezing and thawing lowered numbers of <i>Pseudomonas</i>, APC values and microbial ATP content closely correlated. APC estimates were generally accurate to within 1/2 log. The importance of using an ATP assay standard to correct for variable enzyme activity and presence of quenching factors was demonstrated, and improved formulae were developed for optimum assay standard use. Alternate regression methods were evaluated for estimation of APC values but did not yield enhanced accuracy. Only one regression equation was needed for estimating APC values of ground beef containing different types of bacteria stored in various ways. Therefore, little knowledge of ground beef history is needed in order to rapidly and accurately estimate microbial numbers in ground beef using the bioluminometric ATP assay. / Ph. D.

Since sweet potatoes, which also furnish vitamin A, are a common food in the popular diets of Texas and are so generally grown over the state, the purpose of this study is (1) to ascertain the amount of vitamin C in eight of the varieties most commonly grown and (2) to determine the effect of the three most popular methods of cooking (boiling, baking, and candying) on the vitamin C content of these varieties of sweet potatoes.

Ready-to-eat poultry products, which are precooked so that they can be reheated and served, have gained widespread consumer acceptance. The production of these products generally includes a process that is sufficient to destroy nonsporeforming bacterial pathogens. However, recontamination of these products after the heat process is unavoidable at some level. It could occur during processing steps where the precooked products are handled or exposed to air or unclean work surfaces, during packaging operations, or during handling by the consumer. Reheating instructions are often targeted toward maintaining the integrity of the packaging material of the product instead of the destruction of microorganisms. The objective of this study was to determine if the reheating instructions for precooked poultry products were adequate to destroy vegetative cells of potential bacterial pathogens. Listeria monocytogenes was used as the test microorganism in this study since it is one of the most heat resistant nonsporeforming pathogens that might contaminate these products. D-values were determined in selected poultry products and thermal death time curves were developed. Various ready-to-eat poultry products were obtained from manufacturing plants and from local grocery stores. The minimum and maximum recommended cook times for both microwave and conventional ovens were evaluated in triplicate for all the products. A Campbell Scientific Inc. 21X Micrologger and type T thermocouples and a Luxtron 755 Multichannel Fluoroptic Thermometer and MSA probes were used to record the subcutaneous and internal temperatures of the products heated in the conventional and microwave oven respectively. Heating curves were constructed from the raw data and F values were calculated using z-value data from the IDT curve. Inoculated pack studies were conducted with L. monocytogenes to confirm calculated data. The reheating instructions of many of the products were inadequate to destroy bacterial pathogens. The surface temperatures were usually sufficient to destroy contamination whereas the internal temperatures usually did not reach adequate levels. Since bacterial contamination generally moves from the exterior of a product toward the interior, it would seem that the inadequate interior temperatures would not be a cause of too much concern. However, during the inoculated pack studies, it appears that surface evaporative cooling allowed for survival of the L. monocytogenes. In summary, the adequacy of the heating process varied within brands, between products, and by packaging materials used. / M.S.