engleski

Microbiological quality of soft, semi-hard and hard cheeses during the shelf-life

Cheeses as ready-to-eat food should be considered as potential source of foodborne pathogens, primarily Listeria monocytogenes. The aim of present study was to determine microbiological quality of soft, semi-hard and hard cheeses during the shelf-life, with particular reference to L. monocytogenes. Five types of cheeses were sampled at different time-points during the cold storage and analyzed for presence of Salmonella and Listeria monocytogenes, as well as lactic acid bacteria, Escherichia coli, coagulase positive staphylococci, yeasts, molds, sulfite reducing clostridia and L. monocytogenes counts. Water activity, pH and NaCl content were monitored in order to evaluate the possibility of L. monocytogenes growth. Challenge test for L. monocytogenes was performed in soft cheese, to determine the growth potential of pathogen during the shelf-life of product. All analyzed cheeses were compliant with microbiological criteria during the shelf-life. In soft cheeses, lactic acid bacteria increased in course of shelf-life period (1.2 - 2.6 log increase), while in semi- hard and hard cheeses decreased (1.6 and 5.2 log decrease, respectively). Soft cheeses support the growth of L. monocytogenes according to determined pH values (5.8-6.5), water activity (0.99-0.94), and NaCl content (0.3-1.2 %). Challenge test showed that L. monocytogenes growth potential in selected soft cheese was 0.43 log10 cfu/g during 8 days at 4 °C. Water activity in semi-hard and hard cheeses was limiting factor for Listeria growth during the shelf-life. Soft, semi-hard and hard cheeses were microbiologically stable during their defined shelf-life. Good manufacturing and hygienic practices must be strictly followed in production of soft cheeses as Listeria-supporting food and be focused on preventing (re)contamination.

cheese ; shelf-life ; L. monocytogenes

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