Chemical composition profiling and antifungal activity of the essential oil and plant extracts of <i>Mesembryanthemum edule</i> (L.) bolus leaves

Abstract

Background: Essential oil from Mesembryanthemum edule leaves have been used by the Eastern Cape traditional healers for the treatment of
respiratory tract infections, tuberculosis, dysentery, diabetic mellitus, laryngitis and vaginal infections. The investigation of bioactive compounds
in the essential oil of this plant could help to verify the efficacy of the plant in the management or treatment of these illnesses.
Materials and methods: Various concentrations of the hydro-distilled essential oil, ranging from 0.005-5 mg/ml, were tested against some fungal strains, using the micro-dilution method. Minimum inhibitory activity was compared with four other different crude extracts of hexane, acetone,
ethanol and aqueous samples from the same plant. The chemical composition of the essential oil, hexane, acetone and ethanol extracts was
determined using GC-MS.
Result: GC/MS analysis of the essential oil resulted in the identification of 28 compounds, representing 99.99% of the total oil. Phytoconstituents
of hexane, acetone and ethanol extracts yielded a total peak chromatogram of fifty nine compounds. A total amount of 10.6% and 36.61% of the constituents were obtained as monoterpenes and oxygenated monoterpenes. Sesquiterpene hydrocarbons (3.58%) were relatively low compared to the oxygenated sesquiterpenes (9.28%), while the major concentrated diterpenes and oxygenated diterpenes were 1.43% and 19.24 %, respectively and phytol 12.41%. Total amount of fatty acids and their methyl esters content, present in the oil extract, were found to be 19.25 %. Antifungal activity of the oil extract and four solvent extracts were tested against five pathogenic fungal strains. The oil extract showed antifungal activity against Candida albican, Candida krusei, Candida  rugosa, Candida glabrata and Cryptococcus neoformans with MIC ranges of 0.02-0.31 mg/ml. Hexane extract was active against the five fungal strains with MICs ranging between 0.02-1.25 mg/ml. Acetone extracts were active against C. krusei only at 0.04mg/ml. No appreciable antifungal activity was found in either ethanol or water extracts when compared with commercial antibiotics.
Conclusion: The profile of chemical constituents found in M. edule essential oil and its antifungal properties support the use of M. edule by traditional healers as well as in the pharmaceutical and food industries as a natural antibiotic and food preservative.

Key words: Mesembryanthemum edule, Essential oil, GC/MS, Antifungal activity, Opportunistic fungi