Rice starch molecular size and its relationship with amylose content

The composition and starch molecular structure of eight rice varieties were studied. Waxy and non-waxy (long-, medium-, and short-grain) rice varieties from California and Texas were used. The amylose contents were measured using the Concanavalin A method and were found to be related to the type of rice: waxy approximate to 1.0%, short and medium grain 8.7-15.4%, and long grain 17.1-19.9%. The weight-average molar masses (M-w) of the starches varied from 0.52 to 1.96 x 10(8) g/mol. As would be expected, a higher Mw of rice starch correlated to lower amylose content. The range of Mw of amylopectin was 0.82 to 2.50 x 10(8) g/mol, and there was also a negative correlation of amylopectin M-w with amylose content. Amylose M-w ranged from 2.20 to 8.31 x 10(5) g/mol. After debranching the amylopectin with isoamylase, the weight-average degree of polymerization (DPw) for the long-chain fraction correlated positively with a higher amylose content. California and Texas varieties were significantly different in their amylose content, starch M-w (short- and medium-grain only), and amylopectin M-w (p < 0.05).