Modifying Wheat Bran Dietary Fiber Using High-temperature Steaming with Ultrasound-assisted Compound Enzymatic Method: Process Optimization and Effects on <italic>in Vitro</italic> Probiotic Activity

Defatted wheat bran was modified via high-temperature steaming combined with ultrasound-assisted enzymatic treatments. We investigated the influence of various factors on the yield of soluble dietary fiber (SDF). The physicochemical properties of dietary fibers before and after modification and their effects on in vitro probiotic activity were comparatively analyzed. Steaming coupled with ultrasound-assisted enzymatic treatment increased the yield of wheat bran SDF by 34.31%±0.08%. The optimal process parameters were as follows: liquid-to-solid ratio was 1:10 g/mL, steaming temperature was 120 ℃, steaming duration was 30 min, ultrasound power was 450 W, ultrasound treatment duration was 9 min, ultrasound treatment temperature was 45 ℃, enzyme component (cellulase to hemicellulase) ratio was 1:1, and compound enzyme dosage was 2.5% (w/w). The water-holding, oil-holding, and swelling capacities of the SDF increased by 1.75-, 1.57-, and 1.36-fold relative to the premodification values after modification, respectively. The water-holding, oil-holding, and swelling capacities of insoluble dietary fiber (IDF) increased by 1.15-, 1.28-, and 1.09-fold, respectively, compared with the premodification values. Modified SDF and IDF substantially enhanced the growth and adhesive capacities of Lactobacillus acidophilus and Bifidobacterium longum. These results provide a theoretical basis for the high-value use of wheat bran dietary fiber.