Evaluating antioxidant and antimicrobial activities of essential oils extracted from six plants: Caraway, mint, onion, parsley, fennel, and watercress

Abstract

BackgroundEssential oils extracted from mint, parsley, caraway, onion, fennel, and watercress contain compounds that have different effects on the growth of some microbial strains. These volatile oils can also be used to flavor some foods and preserve foods to extend their shelf life.AimTo identify the composition of extracted volatile oils and know their effect on the growth of some microbial strains.Materials and methodsCommercial samples of six plants (caraway, mint, onion, parsley, fennel, and watercress) were purchased from the local market. Extractions of essential oils from the sample as well as gas chromatography/mass spectrometry analysis were performed. Antimicrobial activity holes (1 cm diameter) were made in the center of Petri dishes containing nutrient agar with 1 ml suspension of the tested microorganisms using a flamed cork borer. Each hole was filled with tested essential oils.ResultsThe results showed that the major components of essential oils of caraway were carvone and limonene (53.69 and 45.23%, respectively), the major components of essential oils of mint were isomenthone and menthol (42.55 and 28.29%, respectively), the major components of essential oils of fennel were estragole and limonene (89.12 and 09.50%, respectively), the major components of essential oils of parsley were valencene, limonene, and pulegone (46.97, 23.09, and 10.56%, respectively), the major components of essential oils of onion were o-cymene and thymoquinone (23.69 and 22.72%, respectively), the major components of essential oils of watercress were estragole (100%). The study investigated the antimicrobial activities of essential oils of mint and parsley to be the best for inhibition of the growth of most tested bacteria, whereas essential oils (50 μl) extracted from caraway, fennel, onion, and watercress did not inhibit the growth of tested bacteria. Essential oils extracted from mint and parsley were tested for antibacterial activity against Salmonella sp., Staphylococcus aureus, Enterococcus, and Citrobacter. The results showed that tested oils of mint and parsley exhibited an inhibitory effect on the growth of the microorganisms Salmonella sp., S. aureus, and Enterococcus. At 200 μl, essential oils extracted from mint did not show inhibition of the growth of Citrobacter and Escherichia coli. However, parsley did not show inhibition of growth of the E. coli at 100, 200, and 300 μl.ConclusionSome of the essential oils (mint and parsley) showed antibacterial activity against Salmonella sp., S. aureus, Enterococcus, and Citrobacter. Some oils did not show inhibition of the growth of Citrobacter and E. coli. These volatile oils can be used to flavor some food and preserve it by extending the shelf life.