Antimicrobial activity of thyme and rosemary essential oils against Listeria monocytogens in Italian mortadella packaged in modified atmosphere

Listeria monocytogenes has been reported as a cause of illnesses related to the consumption raw and processed foods, contaminated during and/or after processing. The ability of L. monocytogenes to multiply at 4°C makes the occurrence in ready-to-eat (RTE) of particular concern. Nowadays, different strategies are applied in order to control pathogens in food products and in particular on the use of essential oils (EOs). The inhibitory effect of thyme and rosemary EOs (0.025% and 0.05%) was determined on a mix of three strains of L. monocytogenes in Italian mortadella packaged in modified atmosphere and stored at 4°C for 30 days. Thymol and p-cymene were the main components of thyme EO, while α-pinene, camphor and eucalyptol of rosemary EO. The use of combined rosemary and thyme EOs exhibited bacteriostatic activity against L. monocytogenes. After 30 days of storage L. monocytogenes charges in treated samples was lower of 2.29 log CFU/g in Group A and 2.79 log CFU/g in Group B compared with control samples. The sensory evaluation, showed the permanence of a strong odor related to EOs used. This work shows that the combined use of thyme and rosemary EOs could be used to control L. monocytogenes in mortadella.