Stability of sliced mozzarella cheese in modified-atmosphere packaging

Twelve slices of mozzarella cheese (about 174 g) were packaged in expanded polystyrene trays placed in gas-barrier bags under three different atmospheres (100% N-2, 100% CO2, and 50% CO2/50% N-2). A gas headspace-to-cheese ratio of 2.5 liters/kg of cheese was initially set in the modified-atmosphere packages, Simulating conventional Brazilian packaging, some trays were wrapped in PVC stretched film. Periodically, the product stored at 7 +/- 1 degrees C was evaluated as to its sensorial quality, microbiological condition, and physical and chemical characteristics. The headspace volume and gas composition of modified-atmosphere packages were evaluated. The mozzarella cheese did not show any physical or chemical alteration in all packaging treatments. These characteristics were not factors which limited shelf life in air or in modified atmospheres, The critical parameter was sensory degradation. The shelf lift of sliced mozzarella in conventional air pack was 13 days, N-2 atmospheres had only a minor effect on shelf life compared with air. Samples under N-2 were satisfactory up to 16 days. A significant shelf life increase was verified under CO2 atmospheres compared with air, as follows: 63 days (a 385% increase) and 45 days (a 246% increase) for product under 100% CO2 and 50% CO2/50% N-2, respectively. The bacteriostatic and fungistatic effects of CO2 were verified. The growth or psychrotrophic bacteria, molds, and yeasts was slower under CO2 atmospheres. Mold and yeast development was inhibited under 100% CO2 (2 liters of CO2 per kg of cheese).