Physicochemical Characterization and Bioactivities of Polysaccharides From <i>Siraitia grosvenorii</i> : Effects of Different Extraction Methods

Five Siraitia grosvenorii polysaccharides (SGPs), namely, SGP-H, SGP-A, SGP-B, SGP-E, and SGP-U, were extracted from hot air-dried fruits using hot water extraction (HWE), acid-assisted extraction (ACAE), alkaline-assisted extraction (ALAE), enzyme-assisted extraction (EAE), and ultrasonic-assisted extraction (UAE), respectively. The extraction yields of ACAE and ALAE were 1.65- and 1.59-fold higher than that of traditional HWE, respectively. Monosaccharide composition analysis showed that SGP-H, SGP-A, SGP-E, and SGP-U were acidic heteropolysaccharides composed of mannose, rhamnose, glucuronic acid, galacturonic acid, glucose, galactose, and arabinose with a notable discrepancy in the molar ratio, whereas SGP-B exhibited the lowest uronic acid content and a unique monosaccharide profile dominated by glucose (76.62%). Comprehensive characterization confirmed significant differences in molecular weight, glycosidic linkage, and surface morphology among the five SGPs. Antioxidant assays indicated that SGP-B exhibited the stronger ABTS and 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity than the other SGPs, with EC₅₀ values of 416 ± 5.4 and 338 ± 14.8 µg/mL, respectively. Meanwhile, immunomodulatory studies on RAW264.7 macrophages revealed that SGP-B significantly enhanced phagocytosis by 29% and stimulated the secretion of immune factors. Therefore, SGP-B, obtained via ALAE, shows great application potential in the development of antioxidants and immunomodulators, and further research deserves attention.