Evolution of microbial counts and chemical and physico-chemical parameters in high-moisture Mozzarella cheese during refrigerated storage

The microbiological quality, pH, colour, proteolysis and head space composition (using an electronic nose) of several commercial brands of high-moisture Mozzarella cheese produced in Italy were evaluated at the beginning and at the end (5 days) of refrigerated storage in order to evaluate the effect of the acidification system (direct acid addition or use of starter cultures) and storage on the quality of the cheese. A high variability was found for most parameters. At the end of storage all parameters were affected by the mode of acidification and cheese produced by direct acid addition had a significantly lower microbiological quality; counts of psychrotrophs exceeded 107 cfu/g for most samples and microbial counts showed a significant correlation with the residual shelf life. Multivariate analysis confirmed that samples at the beginning and at the end of storage were clearly separated but no grouping based on the mode of acidification was found. The electronic nose was only partially successful (80% correct classification) in classifying the cheeses on the basis of storage time or of microbial counts. This is likely to be due to the variety of brands used in the analysis and to differences in the starter systems or acidification mode used.