Insoluble dietary fiber from wheat bran retards starch digestion by reducing the activity of alpha-amylase

This study investigated effects of insoluble dietary fiber (IDF) from wheat bran on starch digestion in vitro, analyzed the inhibition kinetics of IDF toward a-amylase and discussed the underlying mechanisms. Digestion results showed IDF significantly retarded starch digestion with reduced digestion rate and digestible starch content. Enzyme inhibition kinetics indicated IDF was a mixed-type inhibitor to a-amylase, because IDF could bind a-amylase, as evidenced by confocal laser scanning microscopy. Fluorescence quenching and UV-vis absorption experiments conformed this, found IDF led to static fluorescence quenching of a-amylase, mainly through van der Waals and/or hydrogen bonding forces. This interaction induced alternations in a-amylase secondary structure, showing more loosening and misfolding structures. This may prevent the active site of enzyme from capturing substrates, contributing to reduced a-amylase activity. These results would shed light on the utilization of IDF in functional foods for the management of postprandial blood glucose.

Automated summary

This study investigated the effect of insoluble dietary fiber (IDF) from wheat bran on starch digestion in vitro and explored the underlying mechanisms of IDF's inhibition towards a-amylase. The results showed that IDF significantly slowed down starch digestion and reduced digestible starch content. The enzyme inhibition kinetics revealed that IDF acted as a mixed-type inhibitor to a-amylase, binding to the enzyme and causing alterations in its secondary structure. This interaction hindered the enzyme's activity and prevented it from capturing substrates. These findings have implications for the use of IDF in functional foods for managing postprandial blood glucose.