Dioscorea saponin transforms the structure of truffle exo-polysaccharide and enhances its antioxidant activity

Dioscorea saponin (DS) can increase the exo-polysaccharide production of Tuber melanosporum. In the present study, we assessed the effect of DS on the structure and antioxidant activity of exo-polysaccharide. In the absence of DS, only one exo-polysaccharide (TP1) composed of mannose, rhamnose and glucose was isolated. However, two exo-polysaccharides (STP1 and STP2) were isolated in the presence of DS. STP1 was composed of glucose, galactose and arabinose, and STP2 consisted of rhamnose, glucose, galactose and arabinose. The skeletal structure of TP1, STP1 and STP2 was composed of alpha-D-glucopyranose. The antioxidant activity of exo-polysaccharide exhibited a concentration-dependent manner. The DPPH radical-scavenging rate (61.37%) and total antioxidant activity (50.02%) of STP were higher compared with TP1. The STP increased the DPPH radical-scavenging rate depending on the increase of the maximum rate of the reaction at saturating substrate concentrations (k(cat)), while STP increased the reducing power depending on the k(cat) and affinity of substrate to STP. The inhibitory action of STP on hydroxyl radical generation depended on the blockage of Fe2+ by STP, making it unable to react with H2O2 to form center dot OH, and STP could bind to the Fe2+-H2O2 complex and prevent the Fe2+ from turning H2O2 into product.