Alteration of structural and functional properties of tea polysaccharides after selenylation modification

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Abstract
Selenylation modification is an effective way to improve the nutritional and health effects of tea polysaccharide (TPS), 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) treatment, respectively. These different CSe-TPSs were systematacially compared with ordinary tea polysaccharides (Ord-TPS) and naturally 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 activity of TPS after selenylation were improved as well as their inhibitory effects on carbohydrate digestive enzymes (p < 0.05). The total antioxidant capacity (T-AOC) of PCSe-TPS (selenium content of 240.66 µmol/g) was enhanced by 85.41% compared with Ord-TPS (selenium content of 129.80 µmol/g), while its IC50 values on inhibition of α-amylase and α-glucosidase were significantly lower than other TPS (p < 0.05), which suggested best antioxidant and hypoglycemic activity. Moreover, TPS with higher selenium content and smaller particle size showed better antioxidant and hypoglycemic activities. This research will provide new strategies for application of tea polysaccharides.

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