Cumin essential oil: Phytochemical analysis, antimicrobial activity and investigation of its mechanism of action through scanning electron microscopy.

In this study, the antimicrobial effects of cumin essential oil (CEO) and its mechanism of action through scanning electron microscopy (SEM) against Escherichia coli and Listeria innocua were investigated. The SEM images were taken at 0, 12 and 24 h at the minimum inhibitory concentration (MIC). The chemical composition of CEO was identified through gas chromatography/mass spectrometry (GC-MS). The antimicrobial effects of CEO were evaluated by the methods of Kirby-Bauer, well diffusion agar, microdilution broth and minimum bactericidal/fungicidal concentration (MBC/MFC). Antioxidant activity was examined by the methods of β-carotene/linoleic acid inhibition and 2,2-diphenyl-1-picrylhydrazyl. Total phenol content (TPC) was measured by Folin-Ciocalteu method. The subsequent analysis of CEO through GC-MS revealed that cuminal (28.28%) was the major compound of CEO. CEO showed a high TPC of 89.45 ± 0.78 mg GAE/g. The free radical scavenging activity of CEO (based on IC50) was equal to 9.10 ± 0.63 μg mL-1. In addition, CEO showed a remarkably high inhibitory effect (63%) on β-carotene bleaching via neutralizing hydroperoxides, which are responsible for the oxidation of highly unsaturated β-carotene. The antimicrobial effect increased as a function of essential oil concentration. However, there were no inhibitory effects on E. coli at 5 mg mL-1. The electron micrographs demonstrated that CEO caused an increase in the permeabilization of the cells and disrupted the membrane integrity.