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

The solid-state fermentation, reusing soybean curd residue (SCR) as a solid substrate, was conducted for producing polysaccharides by Flammulina velutipes (F. velutipes). The optimal fermentation conditions were 74.5% of moisture content, 9.69 of inoculum size and 30.27 of C/N ratio by response surface methodology. 59.15 mg/g of polysaccharides were obtained. F. velutipes polysaccharides were subsequently extracted from fermented SCR by ultrasonic assisted extraction. The optimal extract conditions were 30 min, 80 °C, 150 W and 20 of water to solid ratio and 106.74 mg/g of polysaccharides were obtained. Furthermore, the antioxidant and the immunomodulatory activities of polysaccharides were assessed. The results showed that polysaccharides exhibited a strong DPPH radical scavenging activity, SOD-like activity, stimulatory the proliferation of the macrophage, the production of nitric oxide, phagocytosis and the protection on Doxorubicin damage. These could lay the foundation for changing SCR into a nutritious functional food or a food additive.