Converting Spent Coffee Grounds into Bioactive Extracts with Potential Skin Antiaging and Lightening Effects

The aim of this study was to valorize spent coffee grounds (SCG) into bioactive extracts for improving skin health. These extracts were obtained by subcritical water extraction (SWE) at 100 bar and temperatures up to 220 degrees C, in a semicontinuous mode. They were analyzed for phenolic acids, carbohydrates, antioxidant activity (AA) measured by the DPPH assay, ROS-scavenging activity in keratinocyte cells, and elastase and tyrosinase inhibitory activity. SCG extracts collected up to 140 degrees C had higher phenolic acids content (19.9 mg(GA)/g(dry) SCG), higher AA (EC50 of 20.6 mu g mL(-1)), and lower carbohydrate content (38 mgsugars/gdry SCG) than the fraction collected from 140 to 220 degrees C (5.7 mg(GA)/g(dry SCG), EC50 of 132.2 mu g mL(-1), and 286 mg(sugars)/g(dry SCG)). The extracts were proven to have antiaging and skin lightening effects by inhibiting elastase (99% and 97.9%) and tyrosinase (78.6% and 92.1%) activity. The extracts were incorporated in shear thinning and acidic hydrogels for topical application. Release (70%) and permeation studies (65.3 +/- 13.1 g/cm(2)) as well as cytotoxicity assays were performed to evaluate the release and permeation of bioactive compounds and the safety of hydrogels.