High-pressure CO2 processing of fragile food matrices: feasibility study and the effect of nitrogen purging

Non-thermal food preservation techniques offer the possibility of extending shelf life while maintaining product quality. Among these, high-pressure carbon dioxide (HPCD) treatment has attracted considerable attention due to its ability to achieve microbial inactivation and enzyme denaturation under relatively mild thermal conditions. However, its application to fragile food matrices remains limited, as structural degradation often occurs during processing. This study aimed to investigate the mechanisms responsible for this degradation, identify conditions under which structural integrity could be preserved, and evaluate microbial inactivation and shelf-life performance under such conditions. Blueberries were used as a representative fragile food matrix. The effects of temperature, pressure, and contact time on structural degradation were examined, and treatment time was found to be the dominant factor. Structural degradation was eliminated by minimizing treatment time, while complete microbial inactivation was achieved under these conditions. Despite this, the treated samples exhibited internal discolouration and wilting during storage. To eliminate post-treatment structural degradation, nitrogen purging of the treatment vessel headspace was carried out prior to depressurisation. Although this reduced the amount of carbon dioxide present in the vessel, it did not eliminate post-treatment structural degradation. To explain these findings, a thermodynamic model based on a sugar-water surrogate solution was developed to describe the solubility behaviour of carbon dioxide. Together with the pressure-specific volume behaviour of carbon dioxide, the results indicate that rapid exsolution and expansion of dissolved carbon dioxide during depressurisation is the primary cause of structural degradation. The findings of this study show that HPCD treatment can achieve microbial inactivation in blueberries, but its application remains limited by tissue damage observed under all the investigated conditions.