Preparation of polysaccharides from Trichosanthes kirilowii Maxim. and their antioxidant and hypoglycemic activities

In this study, Trichosanthes kirilowii Maxim. polysaccharides (TPs) were prepared by conventional water extraction and alcohol precipitation methods, and the optimal extraction conditions were screened to obtain high-purity TPs with a total sugar content of 94.01% and a trace protein content of 0.3%, which reduced the interference of protein impurities in activity evaluation. The physicochemical properties, structural characteristics, and in vitro antioxidant and hypoglycemic activities of TPs were systematically evaluated. The total sugar and protein contents were determined using classical colorimetric methods, while the TP structure was comprehensively characterized using UV and FT-IR spectroscopies, ion chromatography, gel permeation chromatography, SEM and NMR spectroscopy. Structural characterization confirmed that TP was a neutral heteropolysaccharide with a weight-average molecular weight of 6.92 × 10⁵ Da. It was mainly composed of arabinose, galactose, glucose and galacturonic acid, with typical polysaccharide functional groups and an amorphous porous microstructure. In vitro antioxidant assays showed that TP exerted dose-dependent scavenging effects on DPPH, ABTS, hydroxyl and superoxide anion radicals, with scavenging rates of 95.3%, 93.1%, 93.4% and 94.1%, respectively, at 3.2 mg mL^-1. In H₂O₂-stimulated RAW264.7 cells, TP elevated the activities of CAT, SOD and GSH-Px and reduced MDA accumulation, relieving cellular oxidative damage. Hypoglycemic activity assays revealed that TP inhibited α-amylase and α-glucosidase in a concentration-dependent manner, with inhibitory rates of 79.14% and 84.03%, respectively, at 5 mg mL^-1. In insulin-resistant HepG2 cells, TP increased cellular glucose consumption by 35.28% at the optimal concentration and ameliorated hepatocyte insulin resistance. This study preliminarily clarified the relationship between TP's structural features and its dual antioxidant and hypoglycemic activities. The findings supplement the insufficient systematic structural and functional research on TPs and provide fundamental experimental support for the further development of TPs as natural functional food and hypoglycemic ingredients.