Application of Deep Eutectic Solvents to Prepare Mixture Extracts of Three Long-Lived Trees with Maximized Skin-Related Bioactivities

This study aims to apply deep eutectic solvents (DESs) as safe and efficient extraction media that could yield maximized skin-related bioactivities from a mixture of long-lived trees. Ginkgo biloba L., Cinnamomum camphora (L.) J. Presl., and Cryptomeria japonica (L.f.) D. Don, native to Asia, were examined as potential resources of cosmeceutical products. Various DESs synthesized from cosmetics-compatible compounds were used to prepare leaf extracts. A DES containing glycerol and xylitol yielded the highest extractability for isoquercetin, and was selected as the optimal solvent. Isoquercetin has various bioactivities and was found in the extracts of the leaves of all three trees. Then, a series of mixtures of the tree leaves were prepared according to a simplex-centroid mixture design, and their DES-extracts were tested for skin-related activities, including antioxidant, anti-tyrosinase, and anti-elastase activities. The mixture design resulted in two special cubic models and one quadratic model best fitted for describing the antioxidant and anti-elastase activities, and the anti-tyrosinase activity, respectively. Based on the established models, three different optimal formulations of the three kinds of tree leaves were suggested for maximized responses. The present strategy, which is based on the simplex-centroid mixture design with a DES as the extraction solvent, could be applied to developing new materials from a mixture of natural resources, suitable for the cosmetics and related fields.