Effect of different drying techniques on structural characteristics and bioactivities of polysaccharides extracted from (Lithocarpus litseifolius [Hance] Chun) sweet tea leaves

Sweet tea is made from the leaves of Lithocarpus litseifolius (Hance) Chun, which is an herbal tea widely consumed in Chinese folk. In this study, five drying techniques were applied to dry sweet tea leaves, and the structural characteristics, antioxidant activities, α-glucosidase inhibitory activities, and antiglycation activities of sweet tea polysaccharides (STPs) were systematically evaluated. The extraction yields of STPs ranged from 2.37 to 4.09%, and STPs prepared by hot-air drying had the highest extraction yield. The five polysaccharides exhibited the same constituent monosaccharides, similar preliminary structural characteristics, different molecular weights (M_w), and different molar ratios of constituent monosaccharides. Critically, five STPs solutions exhibited non-Newtonian behavior, and STPs obtained by hot-air drying had the highest M_w and apparent viscosity. Compared with other drying technologies, relatively high total phenolic content was measured in the STPs obtained by freeze-drying (31.32 ± 1.77 mg GAE/g) and hot-air drying (29.13 ± 1.36 mg GAE/g). Furthermore, five STPs exhibited excellent biological properties, including antioxidant activities, α-glucosidase inhibitory activities, and antiglycation activities. Ultimately, the heat map analysis found that the bioactivities of STPs were related to their high M_w and high content of total phenolic. All results suggested that STPs, especially polysaccharides prepared by hot-air drying and freeze-drying, had good development prospects and application values as functional ingredients for the antidiabetic functional food development.