Differences in the chemotype of two native spearmint clonal lines selected for rosmarinic acid accumulation in comparison to commercially grown native spearmint

Abstract

Rosmarinic acid (RA) is a water soluble antioxidant present in many Lamiaceae species at varying levels, including spearmint (Mentha spicata L). Two proprietary spearmint clonal lines, KI110 and KI42, with elevated levels of RA (designated Hi-RA) are currently being grown in Indiana for the commercial extraction of RA. The two Hi-RA clonal lines were selected from a native spearmint genetic background and are distinct in their phytochemical composition relative to native spearmint that is commercially grown for purposes of extraction of volatile oils for flavoring applications (“commercial spearmint”). The aim of this study was to describe the major compositional chemotypic differences between the proprietary Hi-RA native spearmint clonal lines relative to a commercial native clonal line of spearmint grown in Indiana. Leaf tissue samples of KI110, KI42 and the commercial spearmint clonal line were collected from field locations in Indiana during June 2013 for RA quantitation and chemical profiling of the essential oil fraction. RA levels in KI110 and KI42 were significantly higher than the commercial spearmint samples. GC–MS analysis revealed major compositional differences between the Hi-RA and commercial spearmint oils. Carvone was the dominant molecule in the commercial spearmint oil, constituting 54% of its oil content. In contrast carvone was below the detection levels in the oils of the two Hi-RA clonal lines, KI110 and KI42. Limonene, another notable constituent of commercial spearmint, was found in lower amounts in the Hi-RA mint clonal lines. Mint lactone and α-cubebene, the predominant compounds in the oil fractions of Hi-RA clonal lines KI110 and KI42, respectively, were either absent or present in insignificant amounts in the commercial spearmint. Differential amounts of myrcene and 1,8-cineole were observed in the three mint oil samples. The chemical fingerprints of the Hi-RA spearmint clonal lines clearly differentiate them from commercial spearmint and they should therefore be considered distinct, clonal lines of spearmint (M. spicata) with potential heath-promotive properties associated with KI110 and KI42 plant extracts that contain higher level of rosmarinic acid.