Abstract: This study aimed to establish and optimize an ultrasound-assisted ethanol extraction process for grapevine (Vitis vinifera L.) leaf, and to evaluate the in vitro antioxidant and hypoglycemic activities of the purified polyphenol fractions. Taking grapevine leaf as the material, the ultrasonic-assisted extraction method was applied to extract polyphenols. Single-factor experiments combined with a Box-Behnken response surface methodology were employed to optimize the extraction parameters and evaluate their effects on polyphenol yield. The results showed that the optimal extraction technology was as follows: ultrasonic temperature of 69 °C, ultrasonic time of 51 min, ethanol volume fraction of 61%, and liquid to material ratio of 40∶1 (mL∶g). The yield of polyphenols in the crude grapevine leaf extract reached (36.56±0.86) mg/g. After purification with macroporous resin, grapevine leaf polyphenols exhibited strong antioxidant activity in vitro, with IC₅₀ values for DPPH and ABTS⁺ radical scavenging of 0.037 3 mg/mL and 0.091 3 mg/mL, respectively. Meanwhile, the grapevine leaf polyphenols showed significant inhibitory effects against α-amylase and α-glucosidase, with IC₅₀ values of 0.076 3 mg/mL and 0.147 0 mg/mL, respectively. These results indicated that grapevine leaf polyphenols possessed strong antioxidant and hypoglycemic potential, providing a reference for the resource utilization of grapevine leaf agricultural by-products.

Key words: grapevine （Vitis vinifera L.） leaf, polyphenols, response surface methodology, antioxidant activity, hypoglycemic activity