Antioxidant and antibacterial activity of the essential oil and methanol extract from Mentha longifolia Hudson

Mentha spp. has been used as a folk remedy for treatment of nausea, bronchitis, flatulence, anorexia, ulcerative colitis, and liver complaints due to its antinflammatory, carminative, antiemetic, diaphoretic, antispasmodic, analgesic, stimulant, emmenagogue, and anticatharrhal activities. This study was designed to evaluate antimicrobial and antioxidant activities of the essential oil and methanol extract from Mentha longifolia hudson. Total phenolic constituent of the extract was 4.5 g/100 g as gallic acid equivalent. GC–MS analysis of the oil resulted in the identification of 45 constituents, cis-piperitone epoxide, pulegone and piperitenone oxide being the main components.Antioxidant activity was evaluated through 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay and β-carotene/linoleic acid assay. The essential oil and methanol extract were individually tested (disc-diffusion assay and evaluating minimum inhibition concentration (MIC)) against a number of bacteria. The essential oil showed strong antimicrobial activity against bacteria tested whereas the methanol extract almost remained inactive. In contrast, the extract showed much better activity than the essential oil in antioxidant activity assays employed, e.g. in the inhibition of free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) and β-carotene/linoleic acid systems. In the former, the extract was able to reduce the stable free radical DPPH with an IC50 of 55.3 μg/ml while that of the oils was 10630 μg/ml. When compared to BHT, a synthetic antioxidant, both showed weaker antioxidative potential. Similarly, in β-carotene/linoleic acid assay, these samples were not effectively able to inhibit the linoleic acid oxidation; exhibiting only 24% and 36% inhibitions at 2 mg/ml, respectively; both were far below than that of BHT.