Efficacy of Plant Essential Oils against Foodborne Pathogens and Spoilage Bacteria Associated with Ready-to-Eat Vegetables: Antimicrobial and Sensory Screening

Abstract

The objectives of this study were to evaluate the antimicrobial activity of plant essential oils (EOs) against foodborne pathogens and key spoilage bacteria pertinent to ready-to-eat vegetables and to screen the selected EOs for sensory acceptability. The EOs basil, caraway, fennel, lemon balm, marjoram, nutmeg, oregano, parsley, rosemary, sage, and thyme were evaluated. The bacteria evaluated were Listeria spp., Staphylococcus aureus, Lactobacillus spp., Bacillus cereus, Salmonella, Enterobacter spp., Escherichia coli, and Pseudomonas spp. Quantitative antimicrobial analyses were performed using an absorbance-based microplate assay. Efficacy was compared using MIC, the half maximum inhibitory concentration, and the increase in lag phase. Generally, gram-positive bacteria were more sensitive to EOs than were gram-negative bacteria, and Listeria monocytogenes strains were among the most sensitive. Of the spoilage organisms, Pseudomonas spp. were the most resistant. Oregano and thyme EOs had the highest activity against all the tested bacteria. Marjoram and basil EOs had selectively high activity against B. cereus, Enterobacter aerogenes, E. coli, and Salmonella, and lemon balm and sage EOs had adequate activity against L. monocytogenes and S. aureus. Within bacterial species, EO efficacy was dependent on strain and in some cases the origin of the strain. On a carrot model product, basil, lemon balm, marjoram, oregano, and thyme EOs were deemed organoleptically acceptable, but only oregano and marjoram EOs were deemed acceptable for lettuce. Selected EOs may be useful as natural and safe additives for promoting the safety and quality of ready-to-eat vegetables.