The relationship between enzyme hydrolysis and the components of rice starches with the same genetic background and amylopectin structure but different amylose contents

The relationship between starch components and hydrolysis previously focused on starches with different amylose contents (ACs) and amylopectin structures. In this study, starches were isolated from six rice seeds with the same genetic background but different activities of granule-bound starch synthase I. The starch components and enzyme hydrolysis were measured and analysed to reveal their relationships. The results showed that the six rice starches had the same amylopectin structure but different ACs ranging from approximately 1%-15%. The starch component parameters measured by different methods were significantly correlated with each other. The hydrolysis parameters of starch by both alpha-amylase and amyloglucosidase were analysed using three methods including a non-linear fit to the degree of hydrolysis, a first-order kinetics fit to the degree of hydrolysis, and a first-order kinetics fit to the hydrolysis rate, and they had significant correlation each other. Waxy starch had a fast hydrolysis rate and showed a single hydrolysis phase during early hydrolysis, while starch with a high AC had a bi-phasic hydrolysis process. Starch component parameters including the maximum absorption wavelength, iodine blue, AC, and low molecular weight fraction were significantly negatively correlated to the hydrolysis rate of starch. The above results indicated that starches with different ratios of amylose to amylopectin but the same amylopectin structure had significantly different hydrolysis properties. This study could provide some information for rice quality breeding and starch applications through changing the activity of granulebound starch synthase I.