Inactivation Of Microorganisms In Carbon Dioxide At Elevated Pressure

Sterilization of bioactive products is one of the most important operations to many foods and Pharmaceuticals. Thermal processing is a conventional and efficient method for sterilization. However, it will destroy thermally unstable substances. Sterilization with CO₂ at elevated pressure is a nonthermal process that would be suitable for the system including proteins and enzymes, and also for heat-sensitive foods. No residual impurity or poisonous materials would be preserved after treatment of CO₂.E.coli is used as a representative model and studied particularly. E.coli is inactivated remarkably by carbon dioxide at the elevated pressure. The process can be divided into two phases based on the different rate of inactivation: the rate of inactivation is slower at the initial stage and increases sharply at the later stage. The dissolving of CO₂ into the aqueous solution and then diffusion into cells controls the duration and inactivation rate at the early stage. An increase of pressure and temperature enhances the antimicrobial effect of CO₂ under pressure. Inactivation is also affected by agitation and release of pressure. Inactivation of microorganisms like L. brevis, S.cerevisiae and A.coerulea at the elevated pressure of CO₂ is also notable except B.subtitus. Ethanol is an effective and novel aid to intensify inactivation of microorganisms in CO2, which would make the sterilization of pressured CO₂ quicker and more efficient.Mechanical impact of pressure and low environmental pH of the cells suspension during the treatment are not the main cause of inactivation of E.coli under elevated pressure CO₂. E.coli cells after CO₂ treatment are subjected to injury on membranes so as to lose salt tolerance and induce a leakage of intracellular materials. The changes of cells structure and inactivition of several enzymes are observed after treatment. But the most important inactivation mechanism may be the lowering of pH due to the penetration of CO2, which leads to the inhibition of certain metabolic and regulating processes.Microorganisms are protected by some nutrients like lipids and proteins when milk and medium are treated under elevated pressure of CO₂. It is convenient and efficient to use elevated pressure of CO₂ to sterilizing beers because ethanol remains in them.