Effects of ultrasound-assisted extraction on antioxidant activity and bidirectional immunomodulatory activity of Flammulina velutipes polysaccharide

In order to investigate the impacts of ultrasound-assisted extraction (UAE) on Flammulina velutipes polysaccharides (FVPs), the differences between FVPs extracted by ultrasound-assisted extraction (FVPU) and FVPs extracted by hot water extraction (FVPH) were compared in terms of yield, primary compositions, surface microstructure, helix-coil transition structure, molecular weight distribution, antioxidant activity, and bidirectional immunomodulatory activity. Results indicated that UAE changed the above properties of FVPs. Compared with FVPH, higher yield, protein content, and uronic acid content but lower polysaccharide and polyphenol contents were observed in FVPU. UAE changed the surface microstructure, destroyed the triple helix structure, and increased the proportion of low molecular weight polysaccharide components of FVPU. Compared with FVPH, FVPU showed a stronger reducing power and scavenging activities on DPPH radical, hydroxyl radical, and superoxide anion radical. FVPU was a better inhibitor of inflammation compared with FVPH. However, FVPH had a better immunity enhancing effect compared with FVPU. These results were attributed to the cavitation effect of ultrasonic waves on the structure of polysaccharides during the extraction process of UAE. These findings suggested that UAE was an efficient and environmentally friendly method to produce new polysaccharides from F. velutipes for the development of functional foods or nutraceuticals.