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Implications of One-Pass Drying of Rice with Industrial Microwave on Milling Quality
G. ATUNGULU (1), D. L. Smith (1), S. Rogers (2). (1) The University of Arkansas, Fayetteville, AR, U.S.A.; (2) AMTek Microwaves, Cedar Rapids, IA, U.S.A.

The volumetric heating phenomenon associated with microwaves has the potential to achieve rapid, one-pass drying of rice with reduced inter-kernel moisture content (MC) gradients and may improve rice milling quality. The objective of this study was to investigate the effectiveness of microwave heating to achieve one-pass rice drying and determine the implications of the treatment on rice milling quality.  Freshly-harvested, medium-grain rice samples (cv. Jupiter) at initial MC of 23.5% (wet basis) were heated with an industrial microwave set at a frequency of 915 MHz,  power levels of 20, 15, 10, 5 and 2 kW,  for durations of 1, 2, 3 and 4 minutes. The effects of natural and forced air-cooling and tempering of rice after microwave treatment on moisture removal and head rice yield were determined. Results showed that microwave treatments at power levels of 10 kW and 15 kW for three and two minutes respectively, bore much promise in decreasing rice MC  from 23.5% to 13.0%  wet basis. However, the microwave treatments need to be optimized to maintain head rice yield comparable to that of control samples dried with ambient air at 26<sup>o</sup>C and 55% relative humidity.  When optimized and successfully implemented, the new approach of using microwave heating to achieve rapid drying of high-MC rice would significantly benefit the rice industry to reduce head rice yield reduction; the technology may find immediate application especially to dry parboiled rice. 

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