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Microwave power is seen as a promising alternative to conventional methods for drying freshly harvested grains to safe storage moisture levels. In an attempt to elaborate a continuous flow microwave dryer, the optimum operating characteristics of a prototype microwave antenna were investigated during a low power microwave drying simulation with corn at three different moisture content levels (15%, 23% and 30% w.b.). The antenna consisted of a slotted waveguide with the orientation and width of the slots being the main points of investigation. / The optimum angle of the slots with respect to the direction of propagation of the travelling wave was found to be in the neighbourhood of 55° at all moisture contents. Slots 13 mm wide gave better results than the 6 mm ones which are often suggested in literature.

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Conventional thermal kinetics of enzyme inactivation and microbial destruction in fruit juices were studied in the pasteurization temperature range (50 to 90°C). Pectin methylesterase (PME), as the most heat resistant enzyme, in orange juice and Saccharomyces cerevisiae and Lactobacillus plantarum, as the most common spoilage yeast and bacteria, respectively, in apple juice used as indicators were subjected to heat treatment in a well-agitated water bath. Based on gathered time-temperature profiles, effective portions of the come-up (CUT) and come-down (CDT) times (lags) were determined for inclusion in kinetic data handling. The inactivation/destruction kinetics followed typical first-order rate of reactions. / A continuous-flow microwave heating system was set up and evaluated for obtaining kinetic parameters under microwave heating conditions. The outlet temperature was characterized as a function of fluid flow rate, heating volume and initial temperature. / Kinetics of enzyme inactivation and microbial destruction at various temperatures under continuous-flow microwave heating conditions were then evaluated using the technique established above. The rates of inactivation/destruction varied depending on temperature. Taking into consideration the effectiveness of the CUT and contributory thermal inactivation during the CDT, the D-values were found to vary from 38.5 s at 55°C to 1.32 s at 70°C (pH 3.7) for PME, 4.75 s at 52.5°C to 0.378 s at 60°C (pH 3.4) for S. cerevisiae (ATCC 16664) and 14.1 s at 57.5°C to 0.327 s at 65°C (pH 3.4) for L. plantarum (ATCC 14917). / Some non-thermal microwave effects were hypothesized to exist and responsible for such differences between the two heating modes. Enzyme inactivation and microbial destruction were then studied further to evaluate the non-thermal effects. A continuous-flow microwave heating system was developed operating at full power while maintaining sample temperatures below 40°C by circulating a microwave-transparent liquid (kerosene) for immediate removal of heat produced in the juice during microwave exposure. / In order to explain and better characterize the faster rate of inactivation/destruction associated with microwave heating conditions observed in kinetic studies, additional tests were carried out using the second set-up described above, but without the cooling heat exchanger. The temperature of samples of different sizes were allowed to progressively increase under carefully controlled conditions. Inactivation of PME in orange juice (pH 3.7) and destruction of S. cerevisiae in apple juice (pH 3.4) were again used as parameters. The results once again clearly demonstrated superior inactivation/destruction effects under microwave heating which increased with temperature and decreased with sample size. (Abstract shortened by UMI.)

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Thesis (M.Sc.). / Written for the Dept. of Bioresource Engineering. Title from title page of PDF (viewed 2007/08/30). Includes bibliographical references.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 135-142). Also available via the Internet.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 107-112). Also available via the Internet.