Abstract

Essential oils were obtained by hydro distillation of dried leaves from two kinds of Plectranthus tenuicaulis (Hook f.) J. k. Morton grown in Gabon and were analyzed using GC-FID, GC-MS, ¹H and ¹³C NMR. The main constituent was (R), (E)-6,7-epoxyocimene [(E)-myroxide] (72.2 to 83.8%) with small amounts of (Z)-6,7-epoxyocimene (0.6 to 1.3%), (E) and (Z)-β-ocimene (1.1 to 2.4% and 0.6 to 1.7%). The oils were examined for their antioxidant, antimicrobial and antibacterial activities. The antioxidant activity was tested by using an in vitro radical scavenging activity test and β-carotene-linoleic acid assays. The essential oils showed antioxidant and DPPH radical scavenging activities, and they displayed the inhibition of lipid peroxidation. The oils were less effective than butylated hydroxytoluene (BHT). The antimicrobial activity of oils was studied by means of agar disc diffusion and broth microdilution methods. The essential oils of P. tenuicaulis showed antibacterial activity against microorganisms tested; however, they were unable to inhibit the growth of Streptococcus pyogenes and fungal strains. The reference bacteria were the most sensitive to the essential oils. We also observed a significant anticandidal effect.

Key words: Plectranthus tenuicaulis, essential oil, GC-MS, antimicrobial activity; antioxidant activity.

Abbreviation

AME, Antifungal mixture elios; BHT, butylated hydroxytoluene; DPPH, 1,1-diphenyl-2-picrylhydrazil; MBC, minimum bactericidinal concentration; MFC, minimum fungicidal concentration; MIC, minimum inhibitory concentration.