Analysis of Ultrasonic-Microwave Synergistic Enzyme Extraction of Soluble Dietary Fiber from Millet Bran and Its Antioxidant Activity

Ultrasonic­-microwave synergistic enzyme method was used to study the effects of liquid-material ratio, synergistic time, extraction temperature and compound enzyme addition on the yield of soluble dietary fiber (SDF) from millet bran. Response surface methodology was used to optimize the process, and the antioxidant activity of soluble dietary fiber from millet bran were analyzed. The results showed that the optimum extraction conditions of SDF from millet bran were as follows: The liquid-material ratio was 31:1 mL/g, the synergistic time was 21 min, the extraction temperature was 56 ℃, and the compound enzyme addition was 1.4%. Under these conditions, the yield of the soluble dietary fiber was 6.35% and its purity was 91.27%. The antioxidant activity showed that when the sample concentration was 14 mg/mL, the SDF reducing power of millet bran was 1.219, and its IC₅₀ values for DPPH radical scavenging rate, ABTS⁺ radical scavenging rate and hydroxyl radical scavenging rate were 2.45, 26.15 and 5.98 mg/mL respectively. The results indicated that the SDF from millet bran had good antioxidant activity.