Abstract
Retrogradation of starch in steamed rice grains under sake-making conditions was examined. The enthalpy change derived from retrogradation of amylopectin increased during the koji and sake mash processes. Ethanol in the sake mash accelerated retrogradation of amylopectin. Enzyme digestibility and properties of endosperm starches of 136 Japanese rice samples used for sake production were examined. A digestion test of steamed rice grains was conducted after 24 h storage at 15°C to estimate more accurately digestibility during the sake-making process. The ratio of short-to-long chain amylopectin exhibited a significant correlation with enzyme digestibility, suggesting that the structure of amylopectin may be used as a predictor of digestibility. The gelatinization temperature of brown/milled rice and purified starch measured by DSC (differential scanning calorimetry) correlated well with the ratio of short-to-long chain amylopectin and with enzyme digestibility. Furthermore, the pasting temperature of milled rice as measured by RVA (Rapid Visco Analyser) correlated well with the ratio of short-to-long chain amylopectin and with enzyme digestibility. Therefore, DSC and RVA appear to be useful tools for estimating enzyme digestibility of steamed rice grains under sake-processing conditions because the measurements are done rapidly and require only small weights of brown/milled rice flour samples.
