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.