Alteration of Structural and Functional Properties of Tea Polysaccharides After Selenylation Modification

Selenylation modification is an effective way to improve the nutritional and health effects of tea polysaccharide, but the effects of different selenylation methods on the structure and efficacy of polysaccharides remain unclear. In this study, a series of chemically selenized tea polysaccharides (CSe-TPS, selenium content of 129.98 ~ 1454.99 µg/g) were prepared by Na₂SeO₃-HNO₃ method, which were promoted by heating (HCSe-TPS), ultrasound (UCSe-TPS), and pulse electric field (PCSe-TPS) treatments, respectively. These different CSe-TPSs were systematically compared with ordinary tea polysaccharides (Ord-TPS) and natural selenium-enriched tea polysaccharides (NSe-TPS) in aspect of molecular structure and biological functions. The results of molecular structure and apparent morphology showed that the particle size (p < 0.05) and the thermal stability of Ord-TPS were reduced after selenylation modification, while the absolute potential of polysaccharide was increased (p < 0.05), coupled with altered monosaccharide composition and changed apparent morphology. However, the main functional groups and the secondary structure of Ord-TPS did not change. The antioxidant activities of tea polysaccharides after selenylation were improved as well as their inhibitory effects on carbohydrate digestive enzymes (p < 0.05). The total antioxidant capacity of PCSe-TPS (selenium content of 240.66 ± 1.43µmol/g) was enhanced by 85.41% compared with Ord-TPS (selenium content of 129.80 ± 3.42 µmol/g), while its IC₅₀ values on inhibition of α-amylase (2.91 ± 0.18 mg/mL) and α-glucosidase (0.18 ± 0.01 mg/mL) were significantly lower than other tea polysaccharides (p < 0.05), which suggested best antioxidant and hypoglycemic activity. Moreover, tea polysaccharides with higher selenium content and smaller particle size showed better antioxidant and hypoglycemic activities. This research will provide new strategies for the application of tea polysaccharides.