Essential oil composition of five Nepeta species cultivated in Lithuania and evaluation of their bioactivities, toxicity and antioxidant potential of hydrodistillation residue
Essential oils of Nepeta cataria var. citriodora, N. transcaucasica, N. melissifolia, N. sibirica and N. nuda were investigated. The yields of EO were from 0.78 (N. nuda) to 5.94 (N. cataria) mg/g plant dry weight (pdw). In total, 143 compounds were identified and quantified in Nepeta plant EOs by GC-MS/FID. 4aα,7α,7aβ-Nepetalactone (NL) was dominant constituent in N. cataria and N. nuda EO (50.16 and 55.72%, respectively) followed by 4aα,7α,7aα-NL (35.64 and 6.20%, respectively); other quantitatively important compounds were β-caryophyllene, caryophyllene oxide, some monoterpene alcohols and their aldehydes. N. transcaucasica EO was composed mainly of citronellol (17.69%), 4aα,7β,7aα-NL (14.34%), geranial (9.05%) and geranyl acetate (8.20%), whereas EOs of N. melissifolia and N. sibirica contained high percentages of 1,8-cineole (37.35 and 42.58%, respectively) and caryophyllene oxide (22.06 and 20.35%, respectively). In order to valorize EO distillation residues their antioxidant potential was evaluated by several in vitro assays: water extracts were considerably stronger radical scavengers than acetone extracts isolated from the solid EO distillation residue. The bioactivities and toxicological data of Nepeta spp. and their main EO components were assessed based on the most recently reported data.