Size-dependent physicochemical property and functionality of insoluble dietary fiber derived from wheat bran

Insoluble dietary fibers (IDFs) demonstrate healthy benefits, while the impact of particle sizes on their properties is far from understood. This study investigated physicochemical and functional properties of IDFs derived from wheat bran with three different sizes. Results indicated that water-holding capacity, oil-holding capacity and α-amylase activity inhibition of IDF had a positive association with their corresponding size. Meanwhile, grinding progress also influenced particle antioxidant capacity, in which the IDFs with a medium size had the greatest antioxidant activity in term of DPPH, ABTS+ and FRAP, which might indicate the importance of appropriate processing for guaranteeing a greater exposure of functional groups. In contrast, extra grinding of IDF led to a lower antioxidant capacity, which might indicate the loss of functional groups on particle surface due to physical action. All IDFs promoted short-chain fatty acids production via gut microbiota fermentation associated with the alteration of gut microbiota. A clinical trial was further performed, and the results indicated that consumption of medium-size IDF increased D-alanyl-d-alanine and decreased kynurenic acid levels in feces, which was positively related to abundance of Romboutsia and NK4A214_group, respectively. This study may contribute to designing individual IDFs for meeting different functional criteria.