Mozzarella cheese in Italy: Characteristics and occurrence of Listeria monocytogenes and coagulase-positive staphylococci at retail

Abstract

Mozzarella cheese is a popular type of fresh cheese, originating from Mediterranean countries and worldwide consumed. As for other soft cheeses, its characteristics might support the growth of Listeria monocytogenes; therefore, the research's aim was to determine the occurrence of L. monocytogenes strains and Listeria spp. on mozzarella cheese at the time of purchase (T0) and at the end of shelf life (Tf). Given the relevance in dairy products, occurrence of coagulase-positive staphylococci was also explored. Retail batches (n = 106) collected in Italy, in supermarkets, discounts and small retailers, were analysed for pH and to detect L. monocytogenes, other Listeria spp. and coagulase-positive staphylococci. Three batches were positive for L. monocytogenes (2.8%; 3/106) and nine (9/106) for other species of Listeria spp. with an occurrence of 10.4% for Listeria spp. Coagulase-positive staphylococci were never detected. Mozzarella cheese showed variability in terms of pH (from 4.30 to 6.24 at T0) and residual shelf life (from 3 to 22 days). This research confirms that L. monocytogenes can be found in mozzarella cheese at retail. However, a low concentration of the pathogen (below the limit of quantification of 10 cfu g−1) was found in the contaminated products at the time of purchase and/or at the end of shelf life. This evidence is relevant since mozzarella cheese is not undergoing further treatment before consumption therefore thus represent the level of contamination to which the consumer might be exposed. Considering the technological steps of mozzarella production, preventing food contamination in food-processing and retail-handling environments is crucial to reduce the level of exposure to the consumer.