Chemotypes and Their Stability in Mentha longifolia (L.) L.-A Comprehensive Study of Five Accessions

Mentha longifolia (L.) L. is the most widespread wild-growing mint species found, and its chemical composition is extremely diverse. We studied the essential oil (EO) yield, composition, and chemotaxonomy of five, northern Hungarian accessions of the species in a cultivation experiment covering two vegetation years at two parallel sites. The long-term goal is to establish the cultivation of this stress-tolerant species in Hungary as a source of flavoring and preservative agents for commercial use. Essential oil yield (1-2 mL/100 g) was observed to be dependent on both the accession and the year. Accession HV1 is assumed to be a new, presumably rare chemotype containing carvacrol (19.28-20.56%), 1,8-cineole (14.87-17.45%), thymol (13.36-13.90%), carvacryl acetate (8.81-10.40%), and para-cymene (7.24-8.01%). Only minor fluctuations occurred in concentrations of these constituents due to habitats and years. A radical change in essential oil composition was observed in accession HV2, as one batch was based on thymol (19.79%) and 1,8-cineole (14.93%), while the others were rich in dihydrocarvone isomers (up to 69%). Although this needs further investigation, it does explain the coexistence of limonene-oxo and γ-terpinene pathways in horsemint. According to the literature, the pathway leading to thymol isomers and/or esters may be rare in the entire Mentha genus. We also demonstrated that known chemotypes of horsemint may differ in variability of their EO composition. Our results also led to the conclusion that any declaration on chemotype needs detailed examination and is not realistic on the basis of a single sample. Assumptions were made about the potential areas of utilization: beside fragrance and flavoring uses of essential oils free from pulegone and menthofurane, thymol-based ones may be used as antioxidative and anti-spoilage agents.