Ultrasonic-Assisted Extraction and Antioxidant Activities of the Polysaccharides Extracted from Soybean Curd Residue Fermented by Flammulina velutipes

The water-soluble polysaccharides content of soybean curd residue fermented by Flammulina velutipes was about 7 times higher than unfermented one and more than 4 times higher than Flammulina velutipes fruiting body. The optimized ultrasonic-assisted extraction method (80 °C, 20 min, 80 W and solid-liquid ratio of 1 g/30 mL) showed a water-soluble polysaccharides extraction yield of 7.88% which was higher than that of hot-water extraction method (6.11%). Moreover, the crude polysaccharides were purified and the main components showed strong activities on DPPH radical scavenging (IC50 0.21 mg/mL), ABTS radical scavenging (IC50 0.42 mg/mL), hydroxyl radical scavenging (IC50 0.28 mg/mL) and SOD-like activity (IC50 0.88 mg/mL). The results indicated that the fermentation method could be used as a new approach for bio-active polysaccharides production and a new method for reusing the food industrial waste. The ultrasonic-assisted extraction method could be considered as a more efficient method in polysaccharides extraction process. Furthermore, the fermented soybean curd residue could be expected as a new source of antioxidant with the further research value.