Shelf life evaluation of ricotta fresca sheep cheese in modified atmosphere packaging

Ricotta fresco cheese is the product of Sardinian dairy industry most exposed to microbial post-process contamination. Due to its technological characteristics, intrinsic parameters, pH (6.10-6.80) and water activity (0.974-0.991). it represents an excellent substrate for the growth of spoilage and pathogenic microorganisms which are usually resident in cheese-making plants environments. Generally, ricotta fresco has a shelf life of 5-7 days. For this reason, at industrial level, modified atmosphere packaging (MAP) is used to extend the durability of the product. However, few investigations have been conducted to validate the use of MAP in ricotta fresco. The aim of this work is to evaluate the shelf life of ricotta fresco under MAP. A total of 108 samples were collected from three Sardinian industrial cheese-making plants and analysed within 24 h after packaging and after 7, 14 and 21 days of refrigerated storage. Aerobic mesophilic bacteria, mesophilic and thermophilic cocci and lactobacilli, Enterobacteriaceae and E. coli. L. monocytogenes, Pseudomonas spp., Bacillus cereus, yeasts and moulds, and the chemical physical parameters and composition of the product were determined. At the end of the shelf life. Pseudomonas spp. and Enterobacteriaceae reached high concentrations, 5 to 7 and 3 to 6 log(10) colony forming unit g(-1), respectively. The presence of environmental contaminants indicates that the use of MAP without the appropriate implementation of prerequisite programmes is not sufficient to extend the durability of ricotta fresco. Gas mixture and packaging material should be selected only on the basis of scientific evidence of their effectiveness.