Purpose: The objective of this study is to evaluate the mechanisms of a 4-strain cocktail of lactic acid bacteria (NP51, NP28, NP7 and NP3) against a 3-strain cocktail of Salmonella (Typhimurium, Enteritidis and Newport).
Methods: Salmonella was subjected to treatment with a LAB freeze-dried cocktail and washed LAB cells. Treatments were altered by adding enzymes to determine whether the mechanism of Salmonella inhibition is caused by a protein-based antimicrobial compound. A control of Salmonella was inoculated in MRS broth; additionally, a treatment of Salmonella co-inoculated with LAB product, without enzyme was evaluated for each respective temperature. Samples were stored at 7°C and 37°C and analyzed for viable cell counts of Salmonella and LAB on days 0 and 5 for 7°C and hours 0 and 24 for 37°C.
Results: For both LAB products (washed cells and freeze-dried product) held at 37°C, with and without enzyme there were significantly (P<0.05) less Salmonella (approximately log 6.0 CFU/ml) when compared to the control. The difference between control and treatments carried with and without enzyme at 7°C after 5 days were non-significant. These results suggest that (1) Protein-based compounds are not responsible for inhibition and (2) temperature is a factor for Salmonella reduction with more inhibition of Salmonella at 37°C than at 7°C.
Significance: Understanding the mechanisms of inhibition can result in optimization of the inhibitory effects. It is apparent that the mechanisms vary depending on the temperature and this should be considered during production and use of the LAB product for microbial pathogen inhibition.