Antimicrobial properties of oregano oil (origanum vulgare) against salmonella enteritidis, staphylococcus aureus and listeria monocytogenes in alheira

Background “Alheiras" are traditional, slightly smoked, naturally fermented meat sausages typical of the Northern regions (Trás-os- Montes) in Portugal and have become very popular in urban centers. Essential oils (EOs) show good antimicrobial properties, becoming a good natural alternative to the use of chemical preservatives. Oregano EO already demonstrated, in vitro, antimicrobial activity, against Salmonella Enteritidis, Staphylococcus aureus and Listeria monocytogenes. The aim of this study was to investigate the antimicrobial effect of oregano EO against Salmonella spp., L. monocytogenes and St. aureus in paste of “alheira” during storage. Method The experimental conditions were: i) not inoculated paste as control; ii) paste inoculated with cocktail of L. monocytogenes (cLm); iii) paste inoculated with cLm with 4% EO; iv) paste inoculated with cLm with 1.5% EO; v) paste inoculated with cLm with 0.5% EO; vi) paste inoculated with cLm with 0.195% EO; vii) paste inoculated with cLm with 0.0975% EO. The same was done for S. Enteritidis and St. aureus. Each trial was performed in triplicate. Microbiological analyzes and determination of water activity and pH values were performed after 4h, 3, 7, 15 and 21 days of storage at 4 ºC. Results & Conclusions For S. Enteritidis and St. aureus at 4%, ocurred a reduction of ~ 3 log at the beginning of the storage time and, after 7 days, L. monocytogenes were not detected. At 1.5% only S. Enteritidis was not detected after 15 days. At 0.5%, 0.195% and 0.0975%, the reduction (~1-2 log) was only observed at the end storage, for S. Enteritidis and St. aureus. L. monocytogenes decreased slowly over time and a 2-3 log reduction was observed for all concentrations investigated after 15 days and, for the lowest concentrations used, there was ~5 log reduction after 21 days. Counts of lactic acid bacteria were ~109 CFU/ml for all samples and no significant differences in the values of pH and aw were detected. Utilization of EOs could be used as a natural technique to improve the safety of meat and fermented meat products. These results could be useful for the meat industry as a food safety tool; however, the concentration required to achieve an antimicrobial effect in foods might be incompatible with their organoleptic acceptance. This needs to be further investigated.