Bioprocessing of Wheat Bran by Combined Extrusion and Solid-State Fermentation: Impact on Biopolymer Physicochemical and Functional Properties

This study aimed to investigate the effects of thermo-mechanical treatment and solid-state fermentation (SSF) on the structural, physicochemical, and techno-functional characteristics of wheat bran (WB), with a particular emphasis on specific isolated protein fractions, starch, and dietary fibre. WB was subjected to extrusion at different temperatures (90, 115, and 130 °C) and screw speeds (16 and 25 rpm), followed by a 24-h SSF with Liquorilactobacillus uvarum. Changes in chemical composition, hydration properties (water absorption, solubility, swelling capacity), temperature-dependent (30–80 °C) extract viscosity, as well as protein extraction yields and in vitro protein digestibility of isolated protein fractions were systematically evaluated. Extrusion reduced insoluble dietary fibre (IDF) content by 15.7–33.9%, while increasing soluble dietary fibre (SDF) content by 59.1–94.2%, and SSF with L. uvarum additionally increased the SDF fraction by 6.5–7.9%. Regarding technological properties, extrusion increased WB water solubility (WS) up to 14.6%, and 24-h fermentation further enhanced WS, reaching up to 16.3%. Extrusion increased the degree of starch gelatinisation up to 49.1%, whereas fermentation reduced it to 40.7% and decreased the WB extract viscosity by 18.3–24.6%. Furthermore, 24-h SSF enhanced the in vitro digestibility of globulin, gliadin, and glutenin fractions from initial values of 71.3–78.8%, 70.6–75.2%, and 70.2–73.0% to 82.0–85.6%, 83.3–88.6%, and 79.4–89.0%, respectively. The observed thermo-induced thickening and enhanced digestibility suggest that modified wheat bran has potential as a functional bio-ingredient for future application in novel food formulations.