Effect of thyme essential oil against pathogenic microorganisms inoculated on chicken breast

Introduction: Food contamination remains a global concern, increasing interest in natural alternatives to food preservation. Thyme essential oil (TEO) has garnered attention due to its antimicrobial and antioxidant properties. Its application in fresh meat aims to reduce microbial contamination and extend shelf life.

Methods: Solutions of TEO at concentrations of 28 and 14 µl/ml were prepared by diluting the TEO with Tween 80. Chicken breast pieces (25×25×5mm and 5 g) were inoculated with 5×10⁶ cfu/ml of a microbial cocktail (Cocktail A: Escherichia coli and Staphylococcus aureus; Cocktail B: Salmonella Typhimurium and Listeria monocytogenes) standardized by OD600 nm. After 15 minutes, samples were treated by direct surface application with 2 ml of each TEO solution. All samples were stored under aerobic conditions at 3 °C. Decimal dilutions were then prepared and spread-plated onto selective agar plates for enumeration on days 0, 2, 5, 8 and 12. An inoculated chicken breast piece without EO was used as control. Results were expressed as log cfu/g.

Results: Treatment with TEO showed efficacy against pathogenic microorganisms on chicken breast. At t0, Escherichia coli counts were lower in treated samples than in the positive control, with greater reductions at 28 µl/ml. For Staphylococcus aureus, no significant differences (p>0.05) were observed during storage. However, compared with the positive control, reductions of up to 1.1 log cfu/g were achieved at 28 µl/ml. In Salmonella Typhimurium, TEO at 14 µl/ml resulted in greater reductions (up to 1.72 log cfu/g at t12) than 28 µl/ml (1.44 log cfu/g), with significant differences (p<0.001) between treatments. For Listeria monocytogenes, counts increased over time, although values were lower at 28 µl/ml, with reductions against the positive control ranging from 0.77 to 0.94 log cfu/g.

Conclusions: TEO exhibited antimicrobial activity on chicken breast, being most effective against E. coli and Salmonella Typhimurium, less on S. aureus and limited on L. monocytogenes. These findings indicate selective antimicrobial potential for application in poultry safety.