Starch granule size and amylopectin chain length influence starch in vitro enzymatic digestibility in selected rice mutants with similar amylose concentration

In human diet, the products of starch digestion are a major energy source. Starch is stored as water insoluble granules composed of amylose and amylopectin. The susceptibility of starch granule to digestive enzymes is affected by starch granule size, shape, and composition. In this study, starch characteristics and in vitro enzymatic hydrolysis in three rice (Oryza sativa L.) mutants (RSML 184, RSML 278 and RSML 352) with similar amylose concentration (24.3-25.8%) was compared to parent ADT 43 (21.4%). The three mutants had reduced thousand grain weight and starch concentration but higher protein and dietary fiber concentrations. The mutant RSML 352 had small starch granules and reduced short glucan chains [Degree of polymerization (DP) 6-12] compared to the other two mutants (RSML 184 and RSML 278). The mutant RSML 352 had the highest hydrolytic index (HI) and least concentration of resistant starch (RS) compared to the other two mutants and parent rice ADT 43. The two rice mutants (RSML 184 and RSML 278) had reduced HI and increased RS concentration than the parent ADT 43. The results showed that starch granule size and amylopectin structure influence starch enzymatic digestibility and RS concentration.