Microstructure-modified products from stone-milled wheat bran powder improve glycemic response and sustain colonic fermentation

Accumulating evidence indicates carbohydrates that escape digestion from upper gastrointestinal tract can reduce glycemic response, enter the colon where they are fermented by the gut microbiota and thus exert multiple healthy benefits to host. A vertical stone milling process was used to prepare a natural wheat bran powder (SWB) containing pericarp, spermoderm, nucellar layer, aleurone layer, germ, and 15% starchy endosperm of wheat kernel, with the result that protein, amylose, and dietary fiber significantly raised comparing to wheat flour (WF). Two types of products, a powdered drink (SWB-D) and a puffed particle (SWB-P), were extruded from SWB, which underwent a gradient of gelatinization and recrystallization with progressively increased resistant starch (RS) content. Starch-protein complexes were detected in SWB-D and SWB-P, concurrently accounting for lower in vitro digestibility and human glycemic response than those of WF noodles. Intake of SWB-D and SWB-P by healthy volunteers elevated level and extended duration of breath hydrogen indicative of higher gut microbiota fermentation. Therefore, RS and starch-protein complexes formed during extrusion reduce digestibility of SWB and sustain colonic fermentation with health-promoting potential targeting the gut microbiota.