Structural Characterization, Phenolic Acid Modification, and Antioxidant Activities of Polysaccharide From Mogroside Waste Liquid of Siraitia grosvenorii

To improve the comprehensive utilization of Siraitia grosvenorii (Swingle) C. Jeffrey, a novel polysaccharide (SGP) was isolated from the mogroside waste liquid of S. grosvenorii. In addition, ferulic acid–SGP (FA-SGP) and caffeic acid–SGP (CA-SGP) were prepared by modifying SGP with phenolic acid. The structural characteristics and antioxidant activities of the three polysaccharides were analyzed. SGP displayed a pore-like structure and was mainly composed of glucose and xylose with a molecular weight of 2.64 kDa. It was a pyran-type polysaccharide with both α-glycosidic and β-glycosidic bonds. The linkage types were Glcp-(1→D →3)-Glcp-(1→, →4)-Glcp-(1→, →6)-Glcp-(1→, →3,6)-Glcp-(1→. FA and CA were covalently attached to SGP by ester bonds, and the molecular weights of FA-SGP and CA-SGP were 5.34 and 3.83 kDa, respectively. They formed a tightly interconnected reticulation structure. Activities tests demonstrated that compared to the native SGP, FA-SGP and CA-SGP could significantly enhance the antioxidant capacity and improve the protective effects on H₂O₂-damaged SH-SY5Y cells. The regulation of FA-SGP and CA-SGP toward the oxidative stress in SH-SY5Y cells might be related to the Bcl-2/Caspase-3/Bax signaling pathways. In this study, phenolic acid grafts with excellent antioxidant activity were prepared using SGP as the lead compound. This provided a new direction for obtaining S. grosvenorii products with satisfactory bioactivity and a reference for the deep processing of S. grosvenorii industry.