Effects of molecular compositions on crystalline structure and functional properties of rice starches with different amylopectin extra-long chains

Abstract The extra-long chain (ELC) of amylopectin influences molecular compositions of starch. In this study, starches were isolated from 22 rice varieties with different ELCs. Molecular compositions of starch were determined, and their relationships with crystalline structure, gelatinization properties, pasting properties, and enzyme hydrolysis were analysed. The results showed that the starches with different ELCs had significantly different structural and functional properties. The ELC was significantly positively related to setback viscosity and negatively related to relative crystallinity, lamellar peak intensity, swelling power, gelatinization enthalpy, and rapidly digestible starch of retrograded starch. The true amylose content was significantly positively related to retrogradation and negatively related to peak viscosity and hydrolysis degree by α-amylase and amyloglucosidase. The short branch-chain of amylopectin was significantly positively related to lamellar peak intensity, swelling power, hydrolysis degree by α-amylase, and rapidly digestible starch of retrograded starch and negatively related to setback viscosity and resistant starch of retrograded starch. The ratio of short to long branch-chain of amylopectin was significantly positively related to swelling power and hydrolysis degree by α-amylase. The principal component analysis and partial least squares discriminant analysis demonstrated that the low-ELC starches were distinguished from the middle- and high-ELC starches, the middle-ELC starches basically clustered together, but the high-ELC starches were highly dispersed. The above results would provide some new information for rice quality breeding and starch applications by changing the ELC in starch.