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 t o the bacteriostatic action of CO2. The dissolved CO2 in the water-pha se of a food product is strongly dependent on several intrinsic and ex trinsic parameters and will determine the effectiveness of a modified atmosphere packaging configuration. The effect of pH, gas/product rati o, initial %CO2 in the gas-phase, lard content and storage temperature on the amount of dissolved CO2 was screened in a preliminary experime nt. The initial CO2-concentration in the gas-phase and the gas/product ratio turned out to be the two major factors determining the amount o f dissolved CO2. The initial pH also determined significantly the fina l CO2-concentration in the broth. Temperature and lard content were sh own to have only a minor effect on the amount of dissolved CO2 compare d to the above mentioned parameters. This demonstrates the importance of the packaging configuration in the effectiveness of a modified atmo sphere. In a second step, a model was constructed to predict the amoun t of dissolved carbon dioxide in modified BHI-broth as a function of t he gas/product ratio, the initial CO2-concentration and the temperatur e by means of Response Surface Methodology (RSM). A second equation wa s also derived based on Henry's law and was shown to be a powerful too l in the quantification of the effect of intrinsic and extrinsic param eters on the CO2-solubility in food products. The possibility of the u se of the concentration of dissolved CO2 in the water-phase as a deter minative factor for the inhibitory effect of modified atmospheres was examined on Pseudomonas fluorescens. Growth curves at 7 degrees C of P . fluorescens in different packaging configurations (initial %CO2 and gas/product ratio) resulting in equal amounts of dissolved CO2 were co mpared. P. fluorescens was shown to be similarly inhibited by equal am ounts of dissolved CO2-concentrations, independent of the packaging co nfiguration. This demonstrates the potential of the application of the concentration of dissolved CO2 in the water-phase as a parameter to c haracterise a modified atmosphere and its inhibition of certain microo rganisms. (C) 1998 Elsevier Science BN. All lights reserved.