Solvent-dependent phenolic profile and in vitro antioxidant and antimicrobial activities of Vaccinium myrtillus L. leaves

Oxidative stress contributes significantly to the development of chronic diseases, increasing interest in plant-derived antioxidants and antimicrobial agents. While bilberry fruits have been widely investigated, leaves from Northern European hemiboreal wild populations remain underexplored. This study provides a systematic comparative evaluation of the solvent-dependent recovery of phenolic compounds and their associated antioxidant and antibacterial activities from Estonian Vaccinium myrtillus leaves. Extracts were prepared using methanol/water (80:20), ethanol, water, methanol, and acetone. Antioxidant activity was evaluated by DPPH and FRAP assays, while total phenolic content (TPC) was determined using the Folin–Ciocalteu method. Selected extracts were analyzed by LC–ESI/MS in SIM mode. Methanol and hydroalcoholic extracts showed the strongest antioxidant activity and highest phenolic content, with the methanol/water (80:20) extract exhibiting the lowest DPPH IC₅₀ value and highest TPC. LC–ESI/MS analysis tentatively identified phenolic acids and flavonoids, including gallic acid, caffeic acid, rutin, quercetin, and kaempferol. In addition, a preliminary antimicrobial evaluation was conducted using a hydroalcoholic macerate prepared under separate extraction conditions; this extract demonstrated antibacterial activity, particularly against Gram-positive bacteria, with MIC values ranging from 0.10 to 0.40 mg/mL. Significant differences among extraction solvents were confirmed by one-way ANOVA (p < 0.05). These findings highlight the solvent-dependent bioactivity of bilberry leaves and their potential application in functional formulations.