Properties of flours and starches as affected by rough rice drying regime

Flours and starches from rough rice dried using different treatment combinations of air temperature (T) and relative humidity (RH) were studied to better understand the effect of drying regime on rice functionality. Rough rice from cultivars Bengal and Cypress were dried to a moisture content of approximate to12% by three drying regimes: low temperature (T 20degreesC, RH 50%), medium temperature (T 40degreesC, RH 12%), and high temperature (T 60, RH 17%). Head rice grams were processed into flour and starch and evaluated for pasting characteristics with a Brabender Viscoamylograph, thermal properties with differential scanning calorimetry, starch molecular-size distribution with high-performance size-exclusion chromatography (HPSEC), and amylopectin chain-length distribution with high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Lower head rice and starch yields were obtained from the batch dried at 60degreesC which were accompanied by an increase in total soluble solids and total carbohydrates in the pooled alkaline supernatant and wash water used in extracting the starch. Drying regime caused no apparent changes on starch molecular-size distribution and amylopectin chain-length distribution, Starch fine structure differences were due to cultivar. The pasting properties of flour were affected by the drying treatments while those of starch were not, suggesting that the grain components removed in the isolation of starch by alkaline-steeping were important to the observed drying-related changes in rice functionality.