Listeria monocytogenes inhibition by lactic acid bacteria and coliforms in Brazilian fresh white cheese.

Abstract

Minas fresh cheese (MFC), a Brazilian white cheese, is one of the most popular cheeses nationwide. Studies have shown that Listeriamonocytogenes occurrence in this product is generally low, while high populations of coliforms can be found. This study aimed to evaluate the influence ofcoliforms in the behavior of L. monocytogenes in MFC. Pasteurized milk was inoculated with L. monocytogenes and coliforms, and the acidification was made by lactic acid or by the addition of a starterculture. The cheeses of each production were divided into 3 groups and stored at 5 ºC, 12 ºC and cycles of 5 ºC followed by 25 ºC. In predetermined days,samples were taken and L. monocytogenes, coliforms and lactic acid bacteria populations were evaluated, besides the pH, water activity (aw), titratable acidity and NaCl concentration. The inhibition of L. monocytogenes in the presence of coliforms was observed (p < 0.05), except for those samples prepared with lactic acid andstored at temperature cycles. The values of pH and aw were not sufficiently low to cause inhibition; however, titratable acidity was higher in cheesescontaining coliforms. In vitro tests containing lactic acid and L. monocytogenes showed that the bacterium is sensitive to concentration of lactic acid ≥0.3%, indicating that lactic acid produced by coliforms strongly influences the population of L. monocytogenes. Thus, it can be concluded that coliforms negatively impact populations of L. monocytogenes in MFC. We strongly recommend that producersof MFC adopt good hygiene practices to not only avoid contamination with L. monocytogenes, but also coliforms.