Behavior of various strains of Yersinia enterocolitica in Ultra-filtered cheese and inhibitory effect of lactic starter bacteria

Abstract

This study aimed to assess the behavior of various strains of Yersinia enterocolitica in ultra-filtered (UF) cheese and to evaluate the inhibitory effect of lactic starter bacteria on survival of Y. enterocolitica. To this end, pasteurized ultra-filtered milk was inoculated with 3 log cfu/g of two standard strains (DSM 11502 and DSM 9499) and one native strain of Y. enterocolitica. UF cheese samples were produced with and without starter culture. Enumeration of Y. enterocolitica was performed at the time of inoculation, after incubation time and during the 2-months storage period on CIN agar. The enumerated colonies were confirmed by PCR. Results revealed that after incubation, the populations of Y. enterocolitica in both groups increased by 4.14 log cfu/g (P < 0.01). However, during the storage period the number of Y. enterocolitica decreased only in the samples made with starter cultures. pH values revealed a significant difference (P < 0.01) between the samples made with and without starter culture; therefore, it seems that acidic pH is the major factor inhibiting the survival of Y. enterocolitica in UF cheese. Besides, a significantly (P < 0.01) different behavior was observed among native and standard strains. Considering the inhibitory effect of starter bacteria,it seems that creation of proper conditions in terms of temperature and the time necessary for proliferation and activity of starter bacteria or application of cultures capable of producing antagonistic products can be effective in controlling possible microbial contaminations along with the development of desirable aroma and texture in UF cheese.

Keywords

• Yersinia enterocolitica
• Ultra-filtered cheese
• Starter cultures