Aroma Chemistry of Mountain Mints in the Incanum Group of Pycnanthemum Michx.

Mountain mints are fragrant plants of the genus Pycnanthemum (Lamiaceae) that grow throughout the eastern United States. The aroma of Pycnanthemum is highly variable suggesting potential food, flavor, and essential oil applications; however, there is limited understanding of the genus’s aroma chemistry. Therefore, we aimed to characterize the aroma of several selections of Pycnanthemum species in the Incanum Group that hybridize with one another to provide a foundational understanding of their aroma chemistry and enable the development of commercially viable varieties. This was achieved through: 1) species verification of four Pycnanthemum selections; 2) aroma characterization of P. pycnanthemoides, P. albescens, and P. loomisii; and 3) comparison of aroma character and odorant composition of P. incanum, P. pycnanthemoides, P. albescens, and P. loomisii.

Morphological evaluation of the Pycnanthemum selections demonstrated the features were consistent with existing literature. Also, high essential oil yields (1.35-3.72%) indicate they could provide a viable source of essential oil. The odorants of each Pycnanthemum species were determined by aroma extract dilution analysis, quantitated by stable isotope dilution assays, and their stereochemistry determined by chiral chromatography. Twenty-eight odorants were identified in P. pycnanthemoides and those with odor activity values (OAV) >1 included β-ionone, piperitenone, piperitone, linalool, myrcene, (R)-(+)-pulegone, (2S,5R)-(−)-menthone, and 1,8-cineole. Likewise, 24 odorants were identified in P. albescens with 1,8-cineole, myrcene, linalool, 𝛽-ionone, borneol, bornyl acetate, and eugenol having OAVs >1. Finally, 38 odorants were identified in P. loomisii with 1,8-cineole, linalool, 𝛽-ionone, borneol, and eugenol having OAVs >1.

Comparing the odorant composition and stereochemistry showed that the P. incanum and P. pycnanthemoidesselections were dominated by mint-like aroma attributes, driven by p-menthane biosynthetically derived odorants (i.e., pulegone, menthone, piperitone, and piperitenone). Conversely, the P. albescens and P. loomisii selections were dominated by the eucalyptus aroma attribute resulting from 1,8-cineole. This work provides the first comprehensive aroma characterizations of Pycnanthemum species, and a foundation for future studies of aroma diversity within the genus, as well as the development of commercially viable varieties for flavor, fragrance, and essential oil applications.