Antimicrobial activity of plant essential oils using food model media: Efficacy, synergistic potential and interactions with food components

• Published in: Food microbiology 2009-04, Vol.26 (2), p.142-150
• Main Authors: Gutierrez, J., Barry-Ryan, C., Bourke, P.
• Format: Article
• Language: English
• Subjects: Animals; antibacterial properties; Antimicrobial; Aroma and flavouring agent industries; bacterial contamination; beef; Biological and medical sciences; Carbohydrates - pharmacology; Colony Count, Microbial; Consumer Product Safety; culture media; Dose-Response Relationship, Drug; Drug Synergism; Enterobacter; Enterobacter - drug effects; Enterobacter - growth & development; Essential oils; Food composition; Food Contamination - prevention & control; Food industries; Food Microbiology; Food model; food pathogens; Food Preservation - methods; food preservatives; Fundamental and applied biological sciences. Psychology; herbs; Humans; Hydrogen-Ion Concentration; Lactobacillus; Lactobacillus - drug effects; Lactobacillus - growth & development; Lactuca - microbiology; lemon balm; lettuce; Listeria; Listeria - drug effects; Listeria - growth & development; Lycopersicon esculentum; marjoram; Meat - microbiology; Melissa officinalis; Microbial Sensitivity Tests; milk; Milk - microbiology; minimum inhibitory concentration; model food systems; natural additives; oregano; Origanum; Origanum - chemistry; Origanum majorana; Origanum vulgare; plant extracts; Plant Oils - pharmacology; Pseudomonas; Pseudomonas - drug effects; Pseudomonas - growth & development; Species Specificity; Synergy; thyme; Thymus; Thymus Plant - chemistry; Thymus vulgaris
• ISSN: 0740-0020; 1095-9998
• DOI: 10.1016/j.fm.2008.10.008

The aim of this study was to optimise the antimicrobial efficacy of plant essential oils (EOs) for control of Listeria spp. and spoilage bacteria using food model media based on lettuce, meat and milk. The EOs evaluated were lemon balm, marjoram, oregano and thyme and their minimum inhibitory concentrations (MIC) were determined against Enterobacter spp., Listeria spp., Lactobacillus spp., and Pseudomonas spp. using the agar dilution method and/or the absorbance based microplate assay. MICs were significantly lower in lettuce and beef media than in TSB. Listeria strains were more sensitive than spoilage bacteria, and oregano and thyme were the most active EOs. EO combinations were investigated using the checkerboard method and Oregano combined with thyme had additive effects against spoilage organisms. Combining lemon balm with thyme yielded additive activity against Listeria strains. The effect of simple sugars and pH on antimicrobial efficacy of oregano and thyme was assessed in a beef extract and tomato serum model media. EOs retained greater efficacy at pH 5 and 2.32% sugar, but sugar concentrations above 5% did not negatively impact EO efficacy. In addition to proven antimicrobial efficacy, careful selection and investigation of EOs appropriate to the sensory profile of foods and composition of the food system is required. This work shows that EOs might be more effective against food-borne pathogens and spoilage bacteria when applied to foods containing a high protein level at acidic pH, as well as moderate levels of simple sugars.