Effect of oregano essential oil on microbiological and physico-chemical attributes of minced meat stored in air and modified atmospheres

Aims: This study aimed to determine the combined effect of packaging (air, modified atmosphere) with or without the addition of essential oil not only on the selection of microbial association of meat but also to determine any significant difference in microbial metabolites produced from the prevailing bacteria. Methods and Results: Samples of minced meat were mixed with different concentration of oregano essential oil (0, 0.05, 0.5 and 1% v/w) and packed under aerobic or with modified atmosphere (Mixed Gas Modified Atmosphere - MGMA, 40% CO2/30% N-2/30% O-2; or CO2 Modified Atmosphere - COMA, 100% CO2) and stored at 5 degreesC. In all packaging conditions, only concentrations of 0.5% and 1% oregano oil were effective. Inhibition was evident in the order air < MGMA < COMA. Oregano essential oil delayed glucose and lactate consumption aerobically as well as under MGMA. pH changes were also evident. Furthermore, proteolysis was significantly inhibited in aerobically stored samples, and so was the production of acetate under MAP. Similar results were obtained for the other organic acids eluted from HPLC column. Conclusions: Oregano essential oil delayed microbial growth and suppressed the final counts of the spoilage micro-organisms. It also caused a pronounced alteration in the physico-chemical properties of the minced meat. Significance and Impact of the Study: Microbial analysis alone as spoilage index may misrepresent the effect of a hurdle such as essential oils on spoilage.