Structural Characterization and Hypoglycemic Activity of Jujube Polysaccharides Extracted by Low-Temperature Pretreatment Combined with Freeze Concentration

In this study, jujube polysaccharides were prepared by four different methods: hot water extraction, freeze-thaw pretreatment (–20 ℃) combined with rotary evaporation concentration (FR), freeze-thaw pretreatment (–20 ℃) combined with freeze concentration (FF), and cryogenic thermostatic reaction bath (–20 ℃) coupled with freeze concentration (CF). Our aim was to systematically explore the effect of low-temperature pretreatment combined with freeze concentration on the extraction efficiency, structural characteristics and in vitro hypoglycemic activity of jujube polysaccharides. Results revealed that cryogenic pretreatment significantly enhanced the hydroxyl (–OH) group content in polysaccharides and better maintained the triple-helix structure compared with traditional hot water extraction. Notably, FF was significantly advantageous in terms of polysaccharide yield, purity and in vitro hypoglycemic efficacy, increasing polysaccharide yield by 105.76%, elevating total sugar content by 25.29%, and reducing half maximal inhibitory concentration (IC50) values for α-glucosidase and α-amylase by 80.1% and 73.4%, respectively compared with traditional hot water extraction. This study provides a new approach for the efficient low-temperature preparation of jujube polysaccharides and offers a theoretical basis for the development and application of natural hypoglycemic products.