Structural and mechanistic insights into the anti-tyrosinase, anti-melanogenesis, and anti-browning effect of proanthocyanidins from seed coats of Acer truncatum Bunge.

Acer truncatum is a multifunctional tree species with broad applications in ornamental, healthy drink, and seed oil. In the present study, proanthocyanidins were isolated from the seed coats of A. truncatum, which were largely discarded as industrial wastes in seed oil production. Meanwhile, structural features, effects and mechanisms of anti-tyrosinase, anti-melanogenesis, and anti-browning of A. truncatum seed coat proanthocyanidins (ASPs) were systematically investigated. The joint application of FT-IR, MALDI-TOF-MS, hiolysis-coupled reverse-phase LC-ESI-MS, together with normal-phase LC confirmed that ASPs were predominately constituted by procyanidins with a mean polymerization degree of 12.09. Furthermore, ASPs powerfully inhibited both monophenolase and diphenolase activities of tyrosinase, and the inhibition of diphenolase was proved to be reversible and competitive-uncompetitive mixed type. Analyses of fluorescence quenching, UV spectra, and copper-ion chelation indicated that ASPs could inhibit tyrosinase in varied stages, and molecular docking and dynamic simulation further revealed the interaction mode between ASPs and tyrosinase. Cell assays further suggested that ASPs exhibited a strong inhibition against intracellular tyrosinase activity and melanin production through suppressing the expression of tyrosinase and microphthalmia transcription factor (MITF) at transcription level and caused apoptosis in B16F10 cells at higher concentrations. Antioxidant and anti-browning studies demonstrated that ASPs possessed high capacities of antioxidant, and potently suppress the browning of fresh-cut potatoes. Therefore, this study confirmed that seed coats of Acer truncatum is a potential natural source of tyrosinase, melanogenesis, and browning inhibitor, which provided a theoretical basis for the utilization of ASPs in the cosmetics, pharmaceutical, and food industries.