Use of protective culture to control the growth of Listeria monocytogenes and Salmonella typhimurium in ready-to-eat cook-chill products

This study explored the antagonistic activity of Lactobacillus rhamnosus GG (LGG) (Culturelle®), a commercial probiotic supplement, on foodborne pathogens and its heat sensitivity in soup products. Staphylococcus aureus, Escherichia coli O157:H7, Escherichia coli O104:H4, L. monocytogenes and S. Typhimurium were selected to assess the inhibitory effect of LGG on them and analyze their sensitivities towards LGG. Cream of potato (CP) and vegetable beef (VB) soups were selected as food matrix to determine thermal resistance of LGG between 55 and 62.5 °C. The effectiveness of LGG as a protective culture against the growth of Listeria monocytogenes and Salmonella Typhimurium was evaluated at conditions simulating the commercial application of cook-chill processing in CP soup and stored at 5, 10 and 15 °C for 21 days. Overall, LGG showed inhibitory effect against all pathogens tested on spot agar test. E. coli O157:H7 was the most sensitive, whereas S. Typhimurium was the least sensitive to the inhibitory effect of LGG. D-values obtained in CP soup exceeded those obtained in VB soup at the temperatures tested. D55-62.5 values of LGG ranged between 0.7-24.2 min and 0.5–15 min in CP and VG soup, respectively. The z-value for CP and VB soup was around 5 °C. LGG co-inoculated with either target bacterium led to a reduction in S. Typhimurium or L. monocytogenes to undetectable levels. The probiotic population increased about 1-log unit at 15 °C. At 10 and 5 °C, it was maintained throughout the experiment at around 108 CFU g−1. Results demonstrated the potential of LGG as protective culture in controlling S. Typhimurium and L. monocytogenes growth in cream of potato soup.