Challenge test studies on Listeria monocytogenes grown in ready-to-eat dry cured pork product stored at home-simulated conditions

Mihail Milanov and Todor Stoyanchev

Abstract: These studies aimed to investigate the survival of Listeria monocytogenes on traditional dry cured sliced meat product – fillet “Elena”. Two batches of sliced product were inoculated with higher and lower concentrations of Listeria monocytogenes, packed under air and stored at 6oC for the first batch and 6, 10 and 25oC for the second one. The storage time for each of them, at each temperature, was 20 days. The storage conditions aimed to simulate the ones, which are most probable to be encountered at consumer homes – air packing of bought products (including post-opening of vacuum packs), storage at low (chill) and high (room temperature) temperatures. Results from the first batch (high) showed a gradual decrease of Listeria monocytogenes concentration from 8.53 log CFU/g (day 0) to 5.53 log CFU/g, (day 20), while the second batch (low) had an increase in concentration at all three temperatures; 5.15 log CFU/g (day 0) to 7.31 log CFU/g (day 20) at 6oC, 5.15 log CFU/g (day 0) to 7.45 log CFU/g (day 20) at 10oC, and 5.15 log CFU/g (day 0) to 7.99 log CFU/g (day 20) at 25oC. The water activity before and after inoculation of the first and second batch were 0.891 and 0.906 and up to 0.906 and 0.921 respectively. Although these values act as a hurdle to prevent the growth of Listeria monocytogenes strains, adding 0.1 ml suspension increased the air packed slices water activity by 0.015, permitting growth on the inoculated strains of the second batch. Performing these types of challenge studies on ready-to-eat products should be an essential step for predicting the growth of pathogenic bacteria in food, in diverse storage conditions.

Keywords: consumer; Listeria monocytogenes; meat product; Ready-to-eat (RTE); storage conditions

Date published: 2022-04-14