Research on antioxidant performance of diglucosyl gallic acid and its application in emulsion cosmetics

Diglucosyl gallic acid is a whitening active with powerful whitening function. When it acts on human skin, microorganisms on the skin surface and part of the stratum corneum produce α-glucosidase to sever the glucose bond of diglucosyl gallic acid, thereby converting part of diglucosyl gallic acid into gallic acid, acting on the skin and exerting the excellent effects of diglucosyl gallic acid and gallic acid at the same time. Diglucosyl gallic acid has high stability and water solubility, it can reduce free radical generation, inhibit tyrosinase generation, prevent melanin transfer, and control skin inflammation. The present study investigates the in vitro tyrosinase inhibition activity, antioxidant capacity of diglucosyl gallic acid as well as its clinical efficacy as a cosmetic ingredient.

Taking VC and gallic acid as controls, the pH = 6.8, 0.05 mmol/L Na2HPO4-NaH2PO4 buffer solution was prepared to test the tyrosinase inhibitory activity and antioxidant capacity of diglucosyl gallic acid respectively. Using arbutin and nicotinamide, two common cosmetic raw materials as controls, 20 volunteers (aged 20-35 years old) were selected for the test. (2 ± 0.1) mg/cm2 take the lotion to be tested and apply it to the test part evenly, twice a day, volunteers are not allowed to use sunscreen or other sunscreen products during the study period.

The results show that diglucosyl gallic acid has a stronger ability to inhibit the activity of tyrosinase compared with VC, and its IC50 value is 2.68 mg/ mL. Their potential antioxidant activities are further evaluated by the DPPH (α, α-diphenyl-β-picrylhydrazyl) method and the ABTS [2,2´-azinobis-(3-ethylbenz othiazoline-6-sulphonate)] radical cation (ABTS+) method, in which the gallic acid demonstrates a better performance than the traditional antioxidant vitamin C (VC), while the diglucosyl gallic acid shows poorer performance. As to the reducing ability, VC has the best performance, much better than gallic acid and diglucosyl gallic acid. Furthermore, through clinical experiments, it is shown the application of the diglucosyl gallic acid as a cosmetic ingredient can considerably improve the brightness of the skin and meanwhile reduce the area of ultraviolet spots, melanin and erythema over time.

The above in vitro and in vivo studies on diglucosyl gallic provide the basis for its future application development in cosmetics.