Thermal Degradation of Starch in Parboiled Rice

Abstract

Abstract Raw and variously parboiled Intan rice (intermediate‐amylose variety) starch was fractionated in Sepharose CL‐2B column into a larger‐molecule (Fr I) and a smaller‐molecule (Fr II) fraction. The amount of Fr I decreased and that of Fr II increased in parboiled as compared to raw rice, the extent of change increasing with increasing severity of processing. The proportion of polysaccharide and “amylose” in Fr I decreased from 70% and 40% of total, respectively, in raw rice to 16% in parboiled rice prepared by 3 kg/cm 2 gauge steam pressure. Simultaneously, the λ max of its iodine complex increased from 570 to 588 nm in Fr I and decreased from 635 to 620 nm in Fr II. The change was marginal or low after steaming at ambient pressure or after sand roasting. The data show that thermal degradation of starch must be considered as another contributor, in addition to starch gelatinization and reassociation, to the peculiar properties of parboiled rice.