Bioactivity of the crude polysaccharides from fermented soybean curd residue by Flammulina velutipes

► Soybean curd residue was reused by Flammulina velutipes to produce polysaccharides. ► Optimum fermentation conditions were obtained by response surface methodology. ► The yield of polysaccharides was improved by ultrasonic assisted extraction. ► Polysaccharides showed DPPH radical scavenging activity and SOD-like activity. ► F. velutipes polysaccharides showed a strong immunomodulatory activities.