Call number: LD2668 .T4 1979 C517 / 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

Whole muscle cuts and restructured chops were conventionally cooked, microwave cooked, and precooked/ microwave reheated. Whole muscle samples had an additional treatment of blade tenderization. All samples were stored for three storage periods of 2, 15, and 21 days. Precooked samples were evaluated for appearance traits. Blade tenderization did not affect (P>0.05) the traits evaluated with the exception of texture. Precooked products had higher (P<0.05) TBA values than conventionally cooked samples of both whole and restructured chops. Conventionally cooked chops had the lowest (P<0.05) TBA value in both whole muscle and restructured cuts, the lowest (P<0.05) peak force value and the highest (P<0.05) sensory scores in whole muscle samples. TBA values increased (P<0.05) with storage time for up to 21 days. Over 21 days of storage of whole muscle samples, Warner-Bratzler peak force values and overall flavor scores decreased (P<0.05) and juiciness and texture scores improved (P<0.05). Storage did not affect (P>0.05) peak force values and sensory scores of restructured samples. / 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

Jerusalem artichoke has been cultivated in various regions without any special breeding technique. On the other hand, in food industry it does not have a wide usage area. Hence, in food industry its use as a potato substitute in some products is believed to be increasing its economical value. As a first attempt chips and crisps produced from Jerusalem artichoke was analyzed for texture, sensory, color, oil and moisture content. Jerusalem artichoke chips were fried in a bench top deep fat fryer for 120s, 180s and 240s at 160&deg / C, 170&deg / C, 180&deg / C and 190&deg / C. When microwave oven was used samples were cooked for 60s, 75s, 90s, 105s, 120s, 135s and 150s at 600 Watt and 900 Watt. Rheological properties of Jerusalem artichoke puree were investigated and Xanthan gum (2%wb) and sodium metabisulphite (1%wb) added for the desired puree consistence and color. After the production of puree Jerusalem artichoke flour was produced and water added to this flour then dough obtained again. Rheological behaviour of the original puree and these prepared from the containing 1- 4.5 and 1 - 5.0 part water were quite similar. In the light of the experimental results obtained as frying temperature and treatment time increased, moisture content and lightness of the Jerusalem artichoke products have decreased but a*and b* values, hardness, fracture and oil content increased. The best results for frying of Jerusalem artichoke seem to be 180&deg / C with about 240s treatment time for the chips and the same temperature for 180s for the crisps. As microwave power level and duration of treatment increased, moisture content and lightness of the microwave cooked Jerusalem artichoke products have decreased, but a* and b* values increased. Hardness and fracturability values of the products first increased with time and then decreased. When microwave oven was used, the best results were obtained for about 105s treatment time at 600W for the Jerusalem artichoke chips and about 60s processing time at 900W for the crisp. Since treatment time for cooking was significantly reduced when microwave cooking was used, this method could be recommended as an alternative to conventional deep fat frying, as oil is not used as well.

Effects of container geometry and material on microwave cooking performance, as measured by evenness of cooking, firmness, and moisture content were compared. Three food items were heated in round, tube, loaf, and square containers made of clear glass, amber glass, thermoset polyester, and polysulfone. Unflavored gelatin, custard, and cakes were prepared three times in each of the 13 microwave containers. Evenness of cooking was determined by comparing meltdown and temperature in gelatin, temperature and separation/uncooked portions in custard, and index to volume in cakes. Firmness was measured in custard while moisture content was determined in cakes. In analysis of the data, ANOVA and Duncan's multiple range test were performed. Significant differences were found between shapes as food items heated more evenly in tube and round containers than in square containers. Food quality was affected more by shape than by material. Foods prepared in the, plastic materials were more evenly heated than in the glass materials. Statistically, shape and material interacted with each other for three measures of microwave appliance performance temperatures and separation/uncooked portions of custards, and index to volume in cakes. The interaction of shape and material was greater as the heating time increased. / Master of Science

Doctor of Philosophy / Department of Diagnostic Medicine/Pathobiology / Douglas Powell / Randall Phebus / Not-ready-to-eat entrées purchased at retail and prepared in the home have been identified as a risk factor for salmonellosis. From 1998 to 2010, ten outbreaks implicated undercooked not-ready-to-eat entrées. In each outbreak, affected individuals prepared entrées in a microwave oven, did not follow recommended cooking instructions, and failed to take the internal temperature of the cooked product. This dissertation surveyed grocery stores for product availability, evaluated consumers’ preparation practices of raw, breaded, frozen chicken entrées, and validated on-package label instructions. The survey of retail revealed that several manufacturers fail to provide consumers clear preparation instructions. A video capture system was used to observe food preparation practices of 41 consumers–21 primary meal preparers and 20 adolescents–in a mock domestic kitchen using uncooked, frozen, breaded chicken products, and determined if differences exist between consumers’ reported safe food handling practices and actual food handling behavior as prescribed on product labels. Differences between self-report and observed food safety behaviors were identified between groups. Many participants reported owning a food thermometer (73 percent) and reported using one when cooking raw, breaded chicken entrées (19.5 percent); however, only five participants (12.2 percent) were observed measuring the final internal temperature with a food thermometer despite instructions on the product packaging to do so. Food handling errors identified during the meal preparation sessions were then mimicked in a controlled laboratory setting to determine the impact of such deviations on end-product temperature. For all products, highly variable internal temperatures were recorded across entrées when prepared in a 600W microwave oven. Microwave cooking of raw breaded poultry products is unpredictable in achieving uniform target end-point temperatures; however, a 1000W microwave oven consistently produced a safe end product. Data collected through direct observation more accurately reflected consumer food handling behaviors than data collected through self-reported surveys. Low wattage microwave ovens failed to produce a safe end product. Processors should validate instructions for not-ready-eat entrées using a range of microwave ovens rather than a single wattage, develop a unique set of instructions for entrées, and provide consumers clear cooking instructions that result in a safe end product.

Call number: LD2668 .T4 1985 B55 / Master of Science