?-Glucosidase Inhibitory And Antioxidant Activities Of Polyphenols In Ampelopsis Grossedentata Leaves

Ampelopsis grossedentata leaves are a kind of polyphenol-rich plant rescource for functional foods.The previous studies about Ampelopsis grossedentata leaves always focus on its polyphenols with low molecular weight,such as dihydromyricetin.There were few reports about its tannins.In view of this,the ultrasonic-microwave synergistic extraction of the polyphenols of Ampelopsis grossedentata leaves was optimized by using the response surface method.The tannin fraction in the water extract was also separated and identified.Then,the ?-glucosidase inhibitory and antioxidant activities of the tannin fraction(TF)and dihydromyricetin(DMY)were systematically compared.With water as solvent,the optimum process for ultrasonic-microwave synergistic extraction was determined as following: ultrasonic power 50 w,extraction time 10 min,ratio of liquid to solid 50:1,microwave power 350 w,microwave time 100 s.Under this condition,the polyphenol yield was 19.35 %,which was expressed as the DMY equivalent.The DMY content of the product obtained by spray drying was as high as 43.08 %.The TF in the water extract of Ampelopsis grossedentata leaves was obtained by using column chromatography.According to UV,IR and NMR analysis,TF was identified as the conjugate of saccharides and gallic acid,which belonged to the gallotannins.In the ?-glucosidase inhibitory assay,the water extract,TF and DMY of Ampelopsis grossedentata leaves showed the ?-glucosidase inhibitory activities.The IC50 values of the water extract,TF and DMY for ?-glucosidase inhibitory capacity were 23.10,1.94 and 72.21 ?g/mL,respectively.The ?-glucosidase inhibitory capacity of TF was far higher than that of DMY.It could be referred that TF was one of the important components responsible for ?-glucosidase inhibitory activity,which could be closely related to the hypoglycemia activity of Ampelopsis grossedentata leaves.The inhibition kinetics test suggested that the inhibition type of the water extract,TF and DMY belonged to a mixed competitive inhibition and non competitive inhibition type.And the fluorescence quenching of ?-glucosidase casued by the water extract,TF and DMY was also observed in the fluorescence analysis.In the reducing power,DPPH and ABTS radical scavenging assays,the water extract,TF and DMY of Ampelopsis grossedentata leaves showed the strong antioxidant activities.The IC50 values of the water extract,TF and DMY for DPPH radical scavenging activity were 15.78,10.17 and 7.66 ?g/mL,respectively.Their corresponding IC50 values for ABTS radical scavenging activity were >60,39.02 and 29.51 ?g/mL,respectively.And the linear relationship between the concentration and the reducing powere of the sample(r2 > 0.996)could be also observed.In the above chemical antioxidant assays,DMY showed the highest activity,followed by TF and the water extract.In the cell medol of HepG2,the water extract,TF and DMY of Ampelopsis grossedentata leaves showed the strong cellular antioxidant activities.In the “no PBS wash” protoctol,the EC50 values of the water extract,TF and DMY for inhibiting the production of the peroxy radical were 80.10,13.13 and 12.56 ?g/mL,respectively.Their corresponding EC50 values in the “PBS wash” protocol were 163.16,30.62 and 78.94 ?g/mL,respectively.The performance of TF was significantly superior to that of DMY.In this study,the ultrasonic-microwave synergistic extraction method of the polyphenolic compounds in of Ampelopsis grossedentata leaves was established.And the tannin fraction in the leaves was separated and identified.It was found that the tannin fraction played the important role in the antioxidant and ?-glucosidase inhibitory functions of the leaves,which could help us to understand the bioactivities of Ampelopsis grossedentata leaves.