Exploring the Bioactive Potential and Biocompatibility of Extracts from Agro-Industrial Residues for Cosmetic Applications

Every year, significant amounts of agro-industrial residues are generated. These residues contain several antioxidant compounds that can be extracted and applied to cosmetic products. In this study, phenolic-rich extracts from different agro-industrial residues (chestnut shell—CS, grape seed—GS, kiwi peel—KP, onion peel—OP, and pomegranate peel—PP) were obtained and their antioxidant potential and biocompatibility towards human fibroblasts (HFF-1) were evaluated. The total phenolic content ranged from 37.6 mg of gallic acid equivalents (GAE)/g for KP to 343.9 mgGAE/g for CS. Moreover, CS, GS, OP, and PP extracts exhibited strong antioxidant properties, while KP showed more moderate potential. Biocompatibility tests demonstrated that CS and GS extracts were non-cytotoxic at concentrations below 500 mg/L, while OP and PP were safe up to 1000 mg/L. KP extracts were biocompatible up to 10,000 mg/L. This work demonstrated the bioactive potential of various agro-industrial residues for application in the cosmetic industry, given their antioxidant capacity. Additionally, it was the first to establish safe application limits for Soxhlet-extracted compounds, ensuring their safety to consumers. This research emphasises the importance of evaluating the biocompatibility of each extract before its incorporation into cosmetics, as their composition is highly variable.