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

[Display omitted] • Insoluble dietary fiber (IDF) apparently reduced starch digestion rate and content. • IDF was a mixed-type (competitive and non-competitive) inhibitor to a -amylase. • α -Amylase could bind to IDF by hydrogen bonding and van der Waals forces. • IDF changed the structure of α -amylase, leading to reduction in enzyme activity. This study investigated effects of insoluble dietary fiber (IDF) from wheat bran on starch digestion in vitro , analyzed the inhibition kinetics of IDF toward α -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 α -amylase, because IDF could bind α -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 α -amylase, mainly through van der Waals and/or hydrogen bonding forces. This interaction induced alternations in α -amylase secondary structure, showing more loosening and misfolding structures. This may prevent the active site of enzyme from capturing substrates, contributing to reduced α -amylase activity. These results would shed light on the utilization of IDF in functional foods for the management of postprandial blood glucose. [ABSTRACT FROM AUTHOR]