Microbial inactivation, mechanism

Two other broad areas of food preservation have been studied with the objective of developing predictive models. En2yme inactivation by heat has been subjected to mathematical modeling in a manner similar to microbial inactivation. Chemical deterioration mechanisms have been studied to allow the prediction of shelf life, particularly the shelf life of foods susceptible to nonen2ymatic browning and Hpid oxidation. 

For instance, if ampules of aqueous products were to be sterilized in a hot air oven, the mechanisms of microbial inactivation would still be by coagulation of intracellular proteins. However, heat transfer from hot air is much slower than heat transfer from steam, which is why this is not seen as a practical process. Microwave irradiation could be an alternative means of sterilizing aqueous pharmaceutical products utilizing the same antimicrobial mechanisms as steam certainly there is evidence that microwave killing patterns are mainly due to heat transfer with very little direct energy being absorbed from the microwaves. 

R. H. Haynes, Role of DNA repair mechanisms in microbial inactivation and recovery phenomena Photochem. Photobiol. 3, 429-450 (1964). 

Finally, the intensive investigations in the past 10 years led supercritical CO2 treatment of food to a promising stage by achieving cold pasteurization and/or sterilization of liquids. Now much more knowledge about the mechanisms of microbial inactivation is available. 

However, lowering of the pH of the media alone cannot describe the inhibition by pressurized CO2. Acids that do not penetrate the microbial cells as readily as CO2 (i.e., hydrochloric acid and phosphoric acid) do not inhibit the cells as greatly (10,11). Another possible mechanism of inactivation is the conversion of bicarbonate to carbonate during system depressurization, which may lead to the precipitation of intracellular ions such as calcium and magnesium (9). 

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