On the behavior of Listeria innocua and Lactobacillus acidophilus co-inoculated in a dairy dessert and the potential impacts on food safety and product's functionality

This study aimed to evaluate the behavior of Listeria innocua in a dairy dessert in the presence/absence of a probiotic microorganism and to assess the in vitro functionality of the probiotic dairy dessert. Three formulations of dairy dessert were prepared: F₁ – inoculated with Lactobacillus acidophilus La-5, F₂ – inoculated with L. innocua and F₃ – inoculated with both L. innocua and L. acidophilus La-5. The dairy desserts were stored at 5 °C/28 days, following measurement of the pH and enumeration of L. innocua and L. acidophilus La-5 on days 0, 7, 14, 21 and 28. The results showed that the pH of the formulation inoculated with L. acidophilus La-5 (F₁) has decreased to 5.6 at the end of the shelf life, while in F₂ (inoculated with L. innocua only) and F₃ (inoculated with L. innocua and L. acidophilus La-5) the pH increased. The counts of L. acidophilus La-5 decreased in F₁ throughout the shelf life, while in F₂ and in F₃, the populations of L. innocua increased, reaching up to 10^8–9 CFU/g at the end of shelf life. The functionality tests indicated that the percentage of survivors decreased (p < 0.05) from 89.3% to 58.8% in F₁ during storage shelf life, while an increase in the percentage of survival of L. acidophilus La-5 (94.0–99.1%, p < 0.05) was observed in F₃. The results of the present study highlight the needs to strictly ensure the microbiological safety of raw materials, control the pasteurization temperature and to guarantee that surfaces and environments are adequately cleaned and sanitized to avoid contamination by Listeria spp., and particularly, by Listeria monocytogenes. Further studies should be carried out to understand the interaction between L. innocua and L. acidophilus La-5.