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Characterization of temperature and quality profiles of rice dried using microwaves for multiple bed thicknesses
D. SMITH (1), G. Atungulu (2), G. Olatunde (2), S. Sadaka (2) (1) The University of Arkansas, Fayetteville, AR, U.S.A.; (2) The University of Arkansas, , U.S.A..

The volumetric heating phenomenon accorded by microwaves (MW) drying of rough rice may reduce inter-kernel temperature and moisture content (MC) gradients, thereby minimizing fissuring and reduction of the rice milling quality. The objective for this research was to determine the impacts of MW energy intensity and heating duration on temperature, MC and quality profiles for rough rice dried at different bed thicknesses. Medium-grain rough rice (cv. Jupiter) at initial MC of 23% (w.b.) was dried using a 915 MHz industrial microwave set to transmit energy at power levels 5, 10, and 15 kW for 4, 6, and 8 minutes and for rice bed thicknesses 5, 10 and 15 cm. Rough rice temperature profiles, percentage points (%pts) MC reduction, pasting parameters, milling quality, microbial load, and sensory characteristics were investigated. Treatments at rice bed thicknesses >5 cm took longer to achieve surface temperatures (100oC to 112oC) necessary for adequate %pts of MC reduction in a single pass (i.e. to MC<13%); the %pts MC reduction increased with increasing specific energy. Rice beds that obtained = 600 kJ/kg-grain had MC=13.0% (w.b.), and the resulting head rice yield (HRY) was not significantly (p>0.05) different from control samples. Heating with energy input exceeding 750 kJ/kg-grain resulted in HRYs drastically lower than that of control samples. Microbial load on rough rice at 23% MC when dried to 14% MC were significantly (p<0.05) reduced compared to control samples. No impact was noted on dried product sensory attributes.

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