Survival of Listeria monocytogenes strains in ultra-filtered white cheese: Effect of Lactobacillus plantarum and incubation period

This study evaluated the effect of Lactobacillus plantarum (Lp) individually or in combination with the extension of incubation period on the survival of native and standard strains of Listeria monocytogenes (Lm) in ultra-filtered white (UFW) cheese throughout the 60 days of storage. Based on the results, in all samples the number of Lm was decreased up to the end of the storage period; however native strain resisted significantly longer than standard strain. Moreover, there was a significant difference in the counts of Lm between the cheeses made with and without Lp (P<0.01). Although the combination of Lp and extension of incubation period was more effective in reducing Lm counts, prolonged incubation period in the Lp-containing samples caused further reduction of pH values. It was concluded that the addition of Lp in comparison to the extension of incubation period could be an effective way to control Lm in UFW cheese. Practical applicationsBased on the findings of this research, despite a slight reduction of Listeria monocytogenes (Lm) population throughout the storage period of ultra-filtered white (UFW) cheese, it can survive up to the end of 60 days of shelf-life. Therefore, the risk of Lm contamination in UFW cheese should not be neglected and may pose a health hazard to the consumers. However, the addition of Lactobacillus plantarum (Lp) as an adjunct starter and the extension of incubation period -either alone or in combination- is highly effective in the elimination of Lm during the storage period of UFW cheese. Native strain of Lm persisted significantly longer than the laboratory-adopted standard strain. Consequently, to create a wider margin of safety for consumers, the behavior of native microbial strains should be considered.