Commercial Mentha Teas as Sources of Bioactive Volatile Compounds: Chemical Composition, Chemotypes, and Antimicrobial Activity

Abstract

Mint (Mentha spp.) teas are widely consumed as functional herbal beverages and represent important dietary sources of bioactive volatile compounds. The present study comparatively evaluated the chemical composition and antimicrobial activity of essential oils (EOs) obtained from commercially available Mentha tea products purchased in Estonia, Lithuania, and Norway. In 10 EO samples studied, 85 compounds were identified by GC–MS. Carvone was the dominant constituent in the carvone chemotype (up to 58.1%), whereas menthol reached 30.7% in the menthol chemotype. Hierarchical clustering of CLRtransformed GC–MS data revealed three well-defined chemotypes among the analyzed Mentha EOs: carvone chemotype (three samples), menthol chemotype (five samples) and mixed, carvone-menthol chemotype (two samples). The antimicrobial activity of EOs was evaluated against 17 clinical antibiotic-sensitive and antibiotic-resistant microorganisms by the agar well diffusion method. The strongest antimicrobial activity was observed against resistant clinical Staphylococcus aureus strains, with MIC values as low as 0.10 mg/mL. EOs with a high carvone content consistently showed higher activity, especially against S. aureus, including resistant phenotypes. In contrast, menthol-chemotype EOs were associated with reduced antibacterial effectiveness. The obtained results demonstrate that the investigated commercial mint teas differ considerably in their phytochemical composition and biological properties, which may contribute to differences in their potential nutraceutical relevance as functional plant-derived beverages.