Specific energy and quality aspects of infrared (IR) dried parboiled rice

Qualities of infrared (IR) dried parboiled rice in terms of head rice yield, colour, percent-gelatinized kernel and specific energy consumption have been evaluated using five levels of radiation intensity (5514, 4520, 3510, 2520 and 1509 W/m(2)) and four levels of grain bed depths (3 mm (single kernel thickness), 6, 12 and 25 mm) in a vibratory IR dryer. Response surface methodology was followed to predict the effect of above mentioned independent parameters on quality variables and specific energy. The major factor in reduction of head yield was observed because of a marked increase in moisture removal rate with the increase in radiation intensity. The drop in percent head yield was about 6-8% for all the grain bed depths, when the intensity increased from 1509 to 5514 W/m(2). Both grain bed depth and radiation intensity influenced the colour (Yellowness Index) of the milled rice at 1% level of significance. The Yellowness Index of the product was found to vary between 30.54 and 52.44. Radiation intensity and bed depth significantly changed the percent gelatinization of the kernels at the 1% level of significance. The percent of gelatinized kernels increased about 8% at maximum bed depth, and 4% at lower bed depths. The variation of specific energy consumption values was between 14.7 and 73.4 MJ/kg at 1% and 5% levels of significance with the increase in radiation intensity and bed depth, respectively. (C) 2003 Elsevier Ltd. All rights reserved.