Concentration of carbon dioxide in the water-phase as a parameter to model the effect of a modified atmosphere on microorganisms

The effect of modified atmosphere packaging can mainly be attributed to the bacteriostatic action of CO2. The dissolved CO2 in the water-phase of a food product is strongly dependent on several intrinsic and extrinsic parameters and will determine the effectiveness of a modified atmosphere packaging configuration. The effect of pH, gas/product ratio, initial %CO2 in the gas-phase, lard content and storage temperature on the amount of dissolved CO2 was screened in a preliminary experiment. The initial CO2-concentration in the gas-phase and the gas/product ratio turned out to be the two major factors determining the amount of dissolved CO2. The initial pH also determined significantly the final CO2-concentration in the broth. Temperature and lard content were shown to have only a minor effect on the amount of dissolved CO2 compared to the above mentioned parameters. This demonstrates the importance of the packaging configuration in the effectiveness of a modified atmosphere. In a second step, a model was constructed to predict the amount of dissolved carbon dioxide in modified BHI-broth as a function of the gas/product ratio, the initial CO2-concentration and the temperature by means of Response Surface Methodology (RSM). A second equation was also derived based on Henryʹs law and was shown to be a powerful tool in the quantification of the effect of intrinsic and extrinsic parameters on the CO2-solubility in food products. The possibility of the use of the concentration of dissolved CO2 in the water-phase as a determinative factor for the inhibitory effect of modified atmospheres was examined on Pseudomonas fluorescens. Growth curves at 7°C of P. fluorescens in different packaging configurations (initial %CO2 and gas/product ratio) resulting in equal amounts of dissolved CO2 were compared. P. fluorescens was shown to be similarly inhibited by equal amounts of dissolved CO2-concentrations, independent of the packaging configuration. This demonstrates the potential of the application of the concentration of dissolved CO2 in the water-phase as a parameter to characterise a modified atmosphere and its inhibition of certain microorganisms.