Inhibition of Salmonella enteritidis in homemade mayonnaise using oregano essential oil (Origanum vulgare)

Abstract

The potential of oregano essential oil (OEO) as a natural antimicrobial agent to mitigate Salmonella spp. contamination in homemade mayonnaise made from raw eggs should be explored. This study aimed to assess the viability of Salmonella Enteritidis in homemade mayonnaise supplemented with OEO while also examining key quality parameters, including pH, titratable acidity, and the count of mesophilic aerobic microorganisms. In vitro experiments determined the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of OEO against two strains of Salmonella Enteritidis and one of Salmonella Typhimurium. Subsequently, homemade mayonnaise, intentionally contaminated with a Salmonella Enteritidis strain, was prepared, and OEO was added at concentrations of 0.5% and 1.0%. Bacterial plate counts for Salmonella spp. and mesophilic microorganisms, as well as acidity levels, were assessed at 0, 4, 8, and 24 hours of incubation at 30°C. The results indicated the in vitro efficacy of OEO, with an MIC of 0.5% and an MBC of 0.0625% against all strains. However, in homemade mayonnaise, Salmonella counts averaged 6.0 log CFU/g over the 24 hours at 30°C. Mesophilic microorganism counts also averaged 6.0 log CFU/g over 24 hours, similar to those of Salmonella. The pH values ranged from 4.5 to 5.1, and acidity levels remained between 0.31% and 0.39% throughout the 24 hours. In conclusion, oregano essential oil exhibited a bacteriostatic effect, effectively limiting the growth of Salmonella Enteritidis in homemade mayonnaise at the evaluated concentrations and time intervals.