Chemical Characterization and In Vitro Evaluation of Antioxidant and Antimicrobial Activities of Vaccinium myrtillus L. Leaves from Estonia

Oxidative stress plays a central role in the development of chronic diseases, increasing interest in natural antioxidants and antimicrobial agents derived from plant sources. Although Vaccinium myrtillus L. (bilberry) fruits are well studied, the bioactive potential of its leaves remains insufficiently explored. In this study, dried leaves collected in Estonia were extracted using five solvents of different polarity (MeOH/H₂O 80:20, EtOH, H₂O, MeOH, and acetone). Antioxidant activity was evaluated in vitro using FRAP and DPPH assays, total phenolic content was determined by the Folin–Ciocalteu method, and selected extracts were qualitatively profiled by LC–ESI/MS in SIM mode. The antimicrobial activity of the aqueous extract was assessed in vitro using an agar-based colony-counting method for minimum inhibitory concentration (MIC) determination. The highest antioxidant activity and phenolic content were observed in methanol and hydroalcoholic extracts, with MeOH/H₂O (80:20) showing the lowest DPPH IC₅₀ and highest TPC values. LC–ESI/MS analysis tentatively identified phenolic acids and flavonoids, including gallic acid, caffeic acid, rutin, quercetin, and kaempferol. The aqueous extract exhibited antibacterial activity, particularly against Gram-positive bacteria (MIC 0.10–0.40 mg/mL). Statistically significant differences among solvent systems were confirmed by one-way ANOVA (p < 0.05). These findings support the solvent-dependent bioactivity of V. myrtillus leaves and their potential application in functional formulations.