Phytochemical Variability of <i>Mentha</i> L. Species Over Three Growing Seasons

Species of the genus Mentha are valued for their aroma and bioactivity. This study presents a comprehensive 3-year (2022-2024) evaluation of two Mentha spicata and three Mentha × piperita genotypes. Methanolic extracts were analyzed for total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity (AA) using spectrophotometry; individual phenolic compounds were determined by HPLC-DAD, and essential oils (EOs) were characterized by GC-MS. Significant inter- and intra-species variability was observed. M. × piperita showed higher phytochemical levels (TPC: 33.61-55.23 mg GAE/g DW; TFC: 27.56-43.01 mg CE/g DW; and AA: 46.48-103.93 mg TE/g DW) than M. spicata (TPC: 28.92-39.57 mg GAE/g DW; TFC: 23.48-35.11 mg CE/g DW; and AA: 40.09-93.59 mg TE/g DW). Rosmarinic acid predominated in all samples (6227.11 to 29321.70 µg/g DW), with elevated levels observed in M. × piperita. EO yields ranged from 0.55% to 2.31% (v/w), with carvone dominant in M. spicata and menthone, dl-menthol, or piperitenone oxide in M. × piperita. Principal component analysis confirmed distinct chemical differentiation among genotypes. Genotype had a strong, and year a moderate, effect on phytochemical profiles. These results highlight the species-specific potential of Mentha for food, pharmaceutical, and cosmetic applications.