The effect of selected preservatives on the growth of Listeria monocytogenes in ready-to-eat foods

Our study evaluated the possibility of survival and growth of L. monocytogenes in 9 types of ready-to-eat foods. The evaluation was focused on the effectiveness of selected preservatives, namely sodium benzoate mixed with potassium sorbate (E 211 and E 202) and a commercially available preservative Defence JB. All delicatessen products were stored at 5 or 6 degrees C. The enumeration of L. monocytogenes was carried out in accordance with the reference ISO method. In most tested products, L. monocytogenes was unable to proliferate and its counts at the end of storage were significantly lower than those at the baseline after the artificial inoculation. This holds true both for samples with preservatives and for those without any preservative. The only exceptions were pasta salad and hard-boiled eggs in mayonnaise, with L. monocytogenes reaching the same (hard-boiled eggs in mayonnaise) or even higher counts (pasta salad) at the end of storage than at the baseline, both in the presence and absence of preservatives. Our results suggest that synergistic effects of intrinsic factors such as pH and a(w) with low storage temperatures plays a greater role in controlling L. monocytogenes growth than the tested preservatives (sodium benzoate/potassium sorbate and Defence JB).