Listeria monocytogenes and Staphylococcus aureus Inhibition by Mexican Oregano (Lippia berlandieri Schauer) Added to Starch Edible Films at Different pH Values

Introduction: Essential oils (EOs) possess antibacterial properties and have been screened as potential sources of novel antimicrobial compounds. EOs could act as biopreservatives, reducing or eliminating pathogenic bacteria and increasing the overall quality of animal and vegetable food products. In this sense, edible films can incorporate these extracts to provide microbiological stability and reduce the risk of microbial growth on food surfaces.

Purpose: The aim of this study was to evaluate the inhibitory effect of starch edible films added with Mexican oregano (Lippia berlandieri Schauer) EO at different pH values on Listeria monocytogenes and Staphylococcus aureus.

Methods: Starch edible films were formulated with Mexican oregano EO concentrations of 0.00, 0.25, 0.50, 0.75, 1.00, or 2.00%, each concentration at pH values of 5, 6, or 7. Minimum inhibitory concentrations (MIC) were determined by agar and broth diffusion methods.

Results: There was a significant difference (P < 0.05) in MIC values between the two diffusion methods. In the agar diffusion method pH values 5 and 6, with 2.00 and 4.00% of EO, inhibit S. aureus and L. monocytogenes, respectively; moreover, the broth diffusion method showed lower MIC values for L. monocytogenes (0.25%), regardless of pH values.  

Significance: Starch edible films, with acid pH values, added with Mexican oregano essential oil, are effective to inhibit Listeria monocytogenes and Staphylococcus aureus.