Chemical Composition of Essential Oils from <i>Nepeta transcaucasica</i> Grossh. and <i>Nepeta cataria</i> L. Cultivated in Bulgaria and Their Antimicrobial and Antioxidant Activity

Abstract

The genus <i>Nepeta</i>, belonging to the family Lamiaceae, includes about 300 species, most of which are used in folk medicine due to their pronounced biological properties. The aim of the present study was to evaluate the agrobiological characteristics of <i>Nepeta transcaucasica</i> (<i>N. transcaucasica</i>) Grossh. and <i>Nepeta cataria</i> (<i>N. cataria</i>) L., cultivated in Bulgaria, and obtain their essential oils and determine their antimicrobial and antioxidant activities. The agrobiological characteristics of the two species growing in Kazanlak were analyzed; therefore, high variability in the population of <i>N. transcaucasica</i> and comparative homogeneity in <i>N. cataria</i> was shown. The species <i>N. transcaucasica</i> contained 0.28% essential oil with main components β-citronellol (52.05%), eucalyptol (7.34%), β-citronellal (6.06%), germacrene D (5.45%), (<i>Z</i>)-β-ocimene (5.14%), and β-caryophyllene (3.06%). The species <i>N. cataria</i> consisted of 0.19% essential oil with main components β-citronellol (26.31%), geraniol (15.92%), neral (11.45%), nerol (9.56%), carvacrol (6.04%), and β-citronellal (5.35%). The antibacterial activity against Gram-positive bacteria <i>Listeria monocytogenes</i> and <i>Staphylococcus aureus</i> and Gram-negative bacteria <i>Escherichia coli</i> (<i>E. coli</i>) and <i>Salmonella enterica</i> subsp. <i>enterica</i> serovar Abony was determined. The essential oils showed antimicrobial activity only against <i>E. coli</i>. The diameters of the inhibition zones were found to be 26 mm for the species <i>N. transcaucasica</i> and 10 mm for the species <i>N. cataria</i>. The antioxidant activity of the two essential oils was also determined by four different methods, DPPH, ABTS, FRAP, and CUPRAC, with the highest values for the ABTS radical, for the species <i>N. transcaucasica</i> (48.72 μM TE/mL), and the species <i>N. cataria</i> (310 μM TE/mL).