Physicochemical, Functional, and In Vitro Fermentation Characteristics of Buckwheat Bran Dietary Fiber Modified by Enzymatic Extrusion

The effects of cellulase–xylanase synergistic treatment combined with twin-screw extrusion on the physicochemical, functional, and in vitro fermentation characteristics of buckwheat bran dietary fiber (BBDF) were investigated. Compared to single enzymatic hydrolysis, the synergetic modification was more effective in promoting the soluble DF (SDF) ratio (increased from 10.68% to 32.67%), functional properties, and prebiotic activities of BBDF and decreasing the insoluble DF (IDF) content. Under 0.6% (w/w) cellulase and xylanase with mild extrusion conditions (40–80 °C), the modified BBDF exhibited the highest capacities for glucose and cholesterol adsorption. FTIR and XRD experiments indicated that the enzymatic extrusion destroyed the intermolecular interactions of BBDF. Furthermore, enzymatically extruded BBDFs showed 2.2-fold higher short-chain fatty acid (SCFA) yields during in vitro fecal fermentation (total SCFAs: 87.8 mM vs. 40.0 mM in control), with butyrate production reaching 2.5 mM (+76.3%), among which the mildly extruded BBDFs exhibited superior prebiotic effects.