Feasibility study and optimisation of an innovative CO2 process for Parmesan cheese pasteurization

The application of high pressure carbon dioxide to solid food matrices is often limited by the severe risk of post-process cross-contamination. To address this critical issue, a novel and advanced high pressure modified atmosphere packaging approach, HPMAP+, has been developed at the Superunit laboratory of the University of Padua. This new technique employs a special packaging material equipped with one-way valves, which allows the direct CO2 treatment of pre-packaged foods. The present study aimed to evaluate and optimise the HPMAP+ technology for the high pressure carbon dioxide pasteurisation of freshly grated Parmigiano Reggiano cheese 24-month ripened. Initially, the treatment efficiency was compared against the previously patented closed-pouch HPMAP method. Subsequently, a design of experiments was implemented to optimise the HPMAP+ process parameters in terms of microbial reduction and colour retention, investigating operative pressures within the range 60-120 bar and treatment times ranging between 0 and 10 minutes at a constant temperature of 40 °C. Finally, a shelf-life study of 42 days was conducted to assess the long-term stability of the treated product. Results indicated that the novel HPMAP+ configuration successfully overcame the physical constraints of the closed-pouch HPMAP, increasing the CO2 amount interacting with the matrix, completely preventing the severe product compaction and the colour shift towards yellow associated with fat exudation. The experimental design identified 90 bar for 10 minutes at 40 °C as the optimal operative condition. This specific combination achieved a substantial reduction of the mesophilic microbial load below the limit of quantification, while minimising the total colour difference. The comprehensive shelf-life investigation confirmed that the HPMAP+ treatment maintained mesophilic, psychrophilic, and moulds-yeasts populations below their respective quantification limits up to 42 days, when combined with a MAP gas mixture (20% CO2 and 80% N2) and stored under stressed refrigerated conditions at 10 °C. Furthermore, treated samples maintained a stable pH < 5.5, whereas untreated control samples exhibited rapid microbial proliferation, severe mould growth, and a significant pH increase. In conclusion, the results highlight the potential of HPMAP+ as a non-thermal pasteurisation technology capable of enhancing microbial safety and extending the shelf-life of grated cheese, while maintaining its delicate physicochemical and structural integrity. The results open the way to further research to investigate the effect of HPMAP+ on other solid dairy products.