Targeting human skin health: Bioactive evaluation of acorn shell and red grape pomace extracts against pathogens and skin cells

The agricultural and food sectors generate substantial amounts of by-products that are usually discarded as waste. However, agri-food by-products, rich in many bioactive compounds (BCs), can find several applications while promoting sustainability. Acorn shell (AS) and red grape pomace (RGP) stand out as valuable sources of BCs. To be used in human skin, the biological properties of these by-products need to be investigated. Therefore, this study explored the chemical composition of AS and RGP extracts and evaluated their concentration-dependent effects on key pathogenic (Staphylococcus aureus) and non-pathogenic (Staphylococcus epidermidis) bacteria of the skin microbiota, as well as on resident skin cells (keratinocytes) and skin cancer cells. The AS extract, rich in phenolic acids and gallotannins, and RGP extract, abundant in flavonoids, demonstrated significant antimicrobial activity by inhibiting bacterial growth and biofilm formation (p < 0.001). Notably, RGP extract exert species-specific effects on biofilm development. In parallel, both extracts showed concentration-dependent effects on cell viability, cell cycle, and cell death in keratinocytes and skin cancer cells. Despite limited effects on IL-10 secretion, their BCs profiles suggest potential anti-inflammatory benefits. AS and RGP extracts show promise for antimicrobial, antibiofilm, anticancer, and anti-inflammatory skin applications, though further research is needed to clarify their molecular mechanisms.