Digestion rate of tapioca starch was lowed through molecular rearrangement catalyzed by 1,4-α-glucan branching enzyme

The 1,4-alpha-glucan branching enzyme (GBE) was used to modify native starch. GBE treatment resulted in the molecular rearrangement of tapioca starch, leading to an increase in the alpha-1,6 linkage content, the weight ratio of the short-chain fraction to the long-chain fraction (SF: LF), the content of cyclic molecules, and a decrease in the average ECL. GBE treatment also suppressed the digestion rate of starch. The magnitude of these changes increased in a time-dependent manner. After a 10-h GBE treatment, the rapidly digestible starch (RDS) content of starch was decreased by 14.5%. The RDS content was negatively related with the alpha-1,6 glycosidic linkage content (R-2=0.8982) and the SF: LF ratio (R-2=0.9646) but positively related with the average ECL of starch (R-2=0.9406). Cyclic structures may also have suppressed the hydrolytic activity of pancreatin and alpha-myloglucosidase. These joint actions of the molecular rearrangements catalyzed by GBE, not just the increase in alpha-1,6 linkage content, provides a mechanistic basis for the digestion rate reduction.