Grain Quality and Properties of Starch and Amylopectin of Intermediate- and Low-Amylose Indica Rices

摘要

Selected intermediate- and low-apparent amylose content (AC) Philippine rices differing in alkali spreading value (index of starch gelatinization temperature, GT) and cooked rice hardness were characterized for differential scanning calorimetry (DSC)measurement of gelatinization of granular starch, content of long-chain amylopectin and true amylose by high-performance size exclusion chromatography of debranched starch and amylopectin, and amylopectin chain ratio (ACR) of I degree of polymerization (DP) 6-10/SIGMA DP 6-24 of debranched starch by capillary electrophoresis. The Waxy gene alleles were mainly 17G and 20G for intermediate-AC samples and 17T and 20T for low-AC samples, regardless of GT. Long-chain amylopectin content was as predicted fromapparent amylose content, and ACR was as predicted from GT by DSC and alkali spreading value. AC of milled rice was higher than that of debranched starch by size exclusion chromatography. Differences in long-chain amylopectin content cannot explain differences in cooked hardness among both AC types, and ACR alone cannot explain differences among intermediate AC type. The lower AC of starch of intermediate-AC rice with intermediate GT compared with those of intermediate-AC rice with low GT probably contributed to its softer cooked rice. Increase in cooked hardness from staling was higher forhigh-and intermediate-GT samples, particularly in iow-AC types.