Polyphenol chemotypes in five clones of horsemint (Mentha longifolia (L.) L.) – New aspects of chemical diversity and utilization

Mentha longifolia (L.) L. (ML) is characterised by polychemism in terms of volatiles and polyphenols. Despite this, ML has not yet been utilized in the industry. The present study involves five different clones in a cultivation experiment covering two sites and three consecutive years. Aims were to clarify the clone-and phenophase-dependent dynamics in polyphenol production and antioxidant indices of the plants as potential polyphenol crops. The concentration of rosmarinic acid (RA) (4011–55145 mg/kg dry weight, DW), eriocitrin (0–45306 mg/kg), luteolin-7-O-rutinoside (161–30848 mg/kg), cynaroside (0–9076 mg/kg) and hesperidin (144–7138 mg/kg) showed significant differences among the clones, assessed by PERMANOVA and classification algorythms. The accumulation of eriocitrin increased in the 2nd-year-old plantations up to 45-fold compared to the 1st year. Peak accumulation of polyphenol content was detected at the first cutting in vegetative shoots except for a single clone, which also demonstrated a second maximum at blooming, both for RA and flavonoids. RA and eriocitrin concentrations demonstrated the strongest correlation with the antioxidant activities of the extracts. Polyphenol-based chemotypes are proposed as a new finding: i) luteolin-7-O-glycosides-flavanone-RA-rich type,ii) luteolin-7-O-rutinoside/RA type, iii) a RA-based type, poorer in flavonoids, distinguishable by the low flavone and eriocitrin content and iv) another RA-based type, in which eriocitrin is absent. Chemotypes rich in RA or flavonoids may have a potential as sources for natural preservatives or phytotherapeutical products. • Five horsemint clones showed diversity in polyphenols over 2 habitats and 3 years. • Rosmarinic acid, eriocitrin, hesperidin, veronicastroside, cynaroside, diosmin detected. • Eriocitrin accumulation enhanced from the 2nd year and hesperidin concentration was depending on habitat. • Four intraspecific chemotypes were proposed, based on polyphenol characteristics. • Clones HOR2 (flavonoid-rich) and EGR3 (RA-rich) or progenies are suggested for industrial use.