The fine Structure of Amylopectin in Endosperm from Asian Cultivated Rice can be largely Classified into two Classes

1 The present investigations have been performed to characterize the structure of amylopectin in endosperm of rice plants cultivated in Asian countries, and to determine the relationship between the amylopectin structure and physicochemical properties of the starch. The results indicated that almost all of rice amylopectin was distinctly classified into L-type or S-type. The L-type amylopectin was diffrent from the S-type amylopectin in that the numbers of short α-1, 4-glucan chains of DP ≤ 10 were less than 20% of the total α-1, 4-glucan chains of DP ≤ 24 in a single cluster in the former and those were higher than 24% in the latter, while no significant difference between both types was found in the proportion of B2 and longer chains of DP ≥ 25. Strikingly, among the 129 rice varieties examined, only a single variety cv. Khauk Yoe belonging to the Tropical Japonica rice group had an intermediate amylopectin structure between L-type and S-type, called M-type amylopectin. Apparently, the proportion of chains with DP ≤10 to those with DP ≤ 24 in amylopectin molecules was negatively correlated with the onset temperature of gelatinization of the starch, whereas no such correlation was observed between the amylose content and the thermal properties of starch. All these results show that the varietal difference in amylopectin structure is predominantly due to difference in lengths of A chains of the cluster and plays a critical role in determining the physicochemical properties of starch in the rice endosperm.