Effect of granular and molecular structure of starch on physicochemical properties and digestibility of dough- and mature-stage rice.

Dough-stage rice has been reported to have higher nutritional composition and antioxidant activity. This study aimed to examine the impacts of composition, molecular order of starch granules, amylopectin chain length distribution, and the Molecular Weight (MW) distribution of starch on digestibility and the nutritional quality. Starch granules in dough-stage rice were larger, more dispersed, and higher crystallinity. Starch digestibility was highly correlated with amylose content, B1 chain, crystalline/amorphous lamellar thickness (Lc, La), and the MW of amylose. The Lc and La in dough-stage were not significantly different from mature-stage, suggesting that amylopectin structure had a lesser effect than amylose content. During maturation, short A and long B3 chains decreased, accompanied by an increase in B1 and B2 chains. B1 chain in dough-stage was positively correlated with resistant starch (RS) and slowly available glucose (SAG) but negatively correlated with rapidly available glucose (RAG). Dough-stage rice could be promoted as a healthy grain.