The Antimicrobial Impact of Essential Oils of Oregano and Thyme on Shelf-Life

One area of food safety concern is shelf stability. Poultry products in particular present challenges to producers, including the potential for spoilage that may pose a threat to consumers. Two essential oils, oregano (O. vulgare) and thyme (T. vulgaris) boast both antioxidant and antimicrobial properties, most likely due to the ability of the phenolic compounds carvacrol and thymol to disrupt the cytoplasmic membranes resulting in spillage of necessary intracellular components. Recently, Pavelkova et al. evaluated the antimicrobial potential of ethylenediaminetetraacetate (EDTA) combined with essential oils of oregano and thyme. To do this, the researchers treated raw chicken breast fillets prior to vacuum packaging and storage at 4 +/- degrees C over 18 days. They used total viable counts (TVC) and selected Pseudomonas aeruginosa and representatives from both Lactobacillus and Enterobacteriaceae to inoculate for colony counts using the appropriate agars (Thermo Scientific). The researchers found that the the control TVC was 4.72 log cfu/g. The lowest TVC values for storage at 4 degrees +/- 0.5 degrees C after 18 days were 3.68 log cfu/g for raw chicken vacuum packed with oregano essential oil and 4.05 log cfu/g for raw chicken vacuum packed with thyme essential oil. Over the course of the study, Enterobacteriaceae counts peaked at 5.66 log cfu/g for the control. Samples that contained essential oils of oregano and thyme demonstrated the absence of this microbe. For Lactobacillus, the results ranged from 2.62 log cfu/g on day 15 to 4.31 log cfu/g on day 3 for the control. Counts for the vacuum packing group ranged from 2.83 log cfu/g on day 15 to 4.31 log cfu/g on day 3. For the vacuum packaging with EDTA group, the range was 1.76 log cfu/g on day 6 to 4.27 log cfu/g on day 0. Samples vacuum packaged with oregano essential oil produced results that ranged from 1.34 on day 15 to 4.32 log cfu/g on day 3. Samples vacuum packaged with thyme essential oil exhibited counts that ranged from 4.29 log cfu/g on day 3 to 1.43 log cfu/g on day 6. Pseudomonas aeruginosa presented in only the control samples and vacuum packaged samples. All samples that contained EDTA or essential oils of oregano or thyme demonstrated the absence of this microbe. Pavelkova et al. report that both carvacrol and thymol present similar antimicrobial activity despite the structural difference of where the hydroxyl group attaches to the phenolic ring. They hypothesized that the demonstrated antimicrobial behavior is a result of either increased movement of cinnamaldehyde into the microbial cell following membrane disruption or increased incidence of pores following the binding of cinnamaldehyde to membrane proteins. The researchers conclude that treatment with essential oils of oregano and thyme may extend shelf-life by as many as 9 days when compared to controls, particularly in the case of gram negative bacteria. They note that the combination of essential oil treatment with vacuum packaging may be a reasonable area for further study. Reference