Kombucha-Mediated Fermentation Enhances Antioxidant, Anti-Inflammatory, Anti-Ageing and Antimicrobial Properties of Fruit Tree Leaf Agro-Waste Extracts from Malus domestica, Prunus armeniaca and Prunus cerasus

Fruit tree leaves are an abundant agro-waste material with promising yet underexplored biological potential. This study compared the biological activity of aqueous extracts obtained from apple (Malus domestica), apricot (Prunus armeniaca), and cherry (Prunus cerasus) leaves and their kombucha-fermented counterparts in the context of cosmetic and dermatological applications. Phytochemical composition before and after fermentation was analyzed chromatographically. Antioxidant activity was evaluated using DPPH, ABTS, and FRAP assays, while intracellular reactive oxygen species (ROS) levels in keratinocytes and fibroblasts were assessed using the H2DCFDA probe. Cytotoxicity was determined by Alamar Blue and Neutral Red assays. Antimicrobial activity against seven bacterial strains was investigated using minimum inhibitory concentration and disc diffusion methods. Anti-inflammatory activity was evaluated in LPS-stimulated THP-1 cells by measuring TNF-α, IL-1β, and IL-6 levels using ELISA. The influence of the samples on collagenase, elastase, and hyaluronidase activity was also analyzed. Fermentation increased the content of selected phenolic compounds and enhanced antioxidant, antimicrobial, anti-inflammatory, and anti-ageing properties. Ferments more effectively reduced oxidative stress in skin cells and showed no cytotoxicity within the tested concentration range. These findings indicate that kombucha fermentation may support the valorization of fruit tree leaf agro-waste as multifunctional ingredients for skincare formulations.