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

Ricotta frescacheese is the product ofSardinian dairy industry most exposed tomicrobial post-process contamination. Due toits technological characteristics, intrinsicparameters, pH (6.10-6.80) and water activity(0.974-0.991), it represents an excellent sub-strate for the growth of spoilage and pathogen-ic microorganisms, which are usually residentin cheese-making plants environments.Generally, ricotta frescahas a shelf life of 5-7days. For this reason, at industrial level, modi-fied atmosphere packaging (MAP) is used toextend the durability of the product. However,few investigations have been conducted to val-idate the use of MAP in ricotta fresca. The aimof this work is to evaluate the shelf life of ricot-ta frescaunder MAP. A total of 108 sampleswere collected from three Sardinian industrialcheese-making plants and analysed within 24h after packaging and after 7, 14 and 21 days ofrefrigerated storage. Aerobic mesophilic bacte-ria, mesophilic and thermophilic cocci and lac-tobacilli, Enterobacteriaceaeand E. coli, L.monocytogenes, Pseudomonas spp., Bacilluscereus, yeasts and moulds, and the chemical-physical parameters and composition of theproduct were determined. At the end of theshelf life, Pseudomonas spp.andEnterobacteriaceaereached high concentra-tions, 5 to 7 and 3 to 6 log10colony forming unitg–1, respectively. The presence of environmen-tal contaminants indicates that the use of MAPwithout the appropriate implementation ofprerequisite programmes is not sufficient toextend the durability of ricotta fresca. Gas mix-ture and packaging material should be selectedonly on the basis of scientific evidence of theireffectiveness.