The regulation of carbon dioxide on food microorganisms: A review

This review presents a survey of two extremely important technologies about CO₂ with the effectiveness of controlling microorganisms - atmospheric pressure CO₂-based modified atmosphere packaging (MAP) and high pressure CO₂ non-thermal pasteurization (HPCD). CO₂-based MAP is effectively in delaying the lag and logarithmic phases of microorganisms by replacing the surrounding air, while HPCD achieved sterilization by subjecting food to either subcritical or supercritical CO₂ for some time in a continuous, batch or semi-batch way. In addition to the advantages of healthy, eco-friendly, quality-preserving, effective characteristic, some challenges such as the high drip loss and packaging collapse associated with higher concentration of CO₂, the fuzzy mechanisms of oxidative stress, the unproven specific metabolic pathways and biomarkers, etc., in CO₂-based MAP, and the unavoidable extraction of bioactive compounds, the challenging application in solid foods with higher efficiency, the difficult balance between optimal sterilization and optimal food quality, etc., in HPCD still need more efforts to overcome. The action mechanism of CO₂ on microorganisms, researches in recent years, problems and future perspectives are summarized. When dissolved in solution medium or cellular fluids, CO₂ can form carbonic acid (H₂CO₃), and H₂CO₃ can further dissociate into bicarbonate ions (HCO₃^-), carbonate (CO₃^2-) and hydrogen cations (H⁺) ionic species following series equilibria. The action mode of CO₂ on microorganisms may be relevant to changes in intracellular pH, alteration of proteins, enzyme structure and function, alteration of cell membrane function and fluidity, and so on. Nevertheless, the effects of CO₂ on microbial biofilms, energy metabolism, protein and gene expression also need to be explored more extensively and deeply to further understand the action mechanism of CO₂ on microorganisms.