In vitro-study of antioxidant extracts from Garcinia mangostana pericarp and Riesling grape pomace - a contribution to by-products valorization as cosmetic ingredients

The objective of the present study was to compare extracts from two different plant sources regarding their suitability as antioxidant cosmetic ingredients. Both, Garcinia mangostana pericarp, in Europe being widely considered as the non-edible part of a 'superfruit', and Riesling grape pomace accruing from vinification, represent important by-products from food processing. Mixtures of ethanol and water in different ratios were used for the preparation of polyphenol containing extracts. Antioxidant properties of the extracts were determined using well-established in vitro assays (Folin-Ciocalteu, ORAC, DPPH, and ABTS), and skin penetration was investigated by Franz-type diffusion experiments with porcine skin. Extraction of polyphenols was most effective using an equimolar ratio of ethanol and water for both raw materials. Absolute polyphenol contents of mangosteen pericarp extract (65360.71 ± 1168.51 mg/kg DM) were higher than for grape pomace extract (18085.70 ± 411.50 mg/kg DM). However, Folin-Ciocalteu reducing capacities as well as in vitro antiradical activities did not adequately correspond to quantitative polyphenol estimations, as grape pomace extract showed relatively high antiradical capacities. When applied to pig skin, polyphenols from grape pomace extract were detected in low concentrations in the dermis as well as in the transdermal receptor fluid. In contrast, mangosteen pericarp xanthones were almost completely recovered with highest amounts detected in the dermis. In conclusion, both raw materials revealed potential as antioxidant ingredients for cosmetic formulations.