Microbiological Quality of Soft, Semi-Hard and Hard Cheeses During the Shelf-Life

Abstract

Original Scientific ArticleMac Vet Rev 2016; 39 (1): [59][60][61][62][63][64] Cheeses as ready-to-eat food should be considered as a potential source of foodborne pathogens, primarily Listeria monocytogenes. The aim of present study was to determine the 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 timepoints during the cold storage and analyzed for presence of Salmonella and L. 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 whey 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 the course of the shelf-life period (1.2-2.6 log increase), while in semi-hard and hard cheeses it 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 log 10 cfu/g during 8 days at 4°C. Water activity in semi-hard and hard cheeses was a 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 the production of soft cheeses as Listeria-supporting food and be focused on preventing (re)contamination. INTRODUCTIONMicrobiological stability and safety of food during storage is related to many factors. Ready-to-eat food products, including cheeses, are intended for consumption without any treatment between final production step and consumption. The course of microbiological changes in different cheeses during storage and shelf-life depends on the production technology and cheese type (pasteurization, starters, acidity, ripening, etc.) MATERIAL AND METHODSSoft, semi-hard and hard cheeses were produced according to standard procedure in a local cheese producing plant and sampled at the end of production. Ten units of each cheese were sampled, stored in laboratory at 4°C and periodically analyzed during defined shelf-life (Table 1). For microbiological analyses, 25 g of sample was diluted in 225 ml of appropriate media (Buffered Peptone Water, Half-Fraser Broth or Peptone salt water) and homogenized for 2 min (Stomacher, Sedward, UK). Serial decimal dilutions were prepared and 0.1 ml or 1 ml of selected dilution were used for evaluation of lactic acid bacteria count (MRS, Merck, Darmstadt, Germany) at 30°C for 48 h, Staphylococcu...

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Comparison of the Chemical Composition of Whey Cheeses: Urda And Ricotta

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