Résumé
Carbon dioxide is the most important gas in Modified Atmosphere Packaging (MAP) systems, usually intentionally added for its bacteriostatic properties for increasing shelf life of non-respiring fresh products. For example, CO2 level between 20 to 30% are usually used for MAP of meat product. In such case of high CO2 headspace concentration, a CO2 transfer from the food and packaging headspace toward external atmosphere occurs, which rate depends on respectively CO2 diffusivity within food and packaging CO2 permeability. Solubility parameter determines the maximal CO2 quantity that could dissolve in the product and CO2 diffusivity, the rate at which this molecule migrates in the product. Historically, dissolved CO2 in the food matrix was calculated using Henry’s law considered only the solubilisation in the aqueous fraction. Recent studies have shown that this shortcut was not relevant for fatty products because CO2 significantly dissolves in the fat fraction. Experimental measurements of CO2 solubility were thus necessary. Furthermore, CO2 diffusivity was scarcely accurately measured, this parameter being almost always neglected in MAP dimensioning. However, both parameters, solubility and diffusivity, are required in mathematical models to predict mass transfer in the food/packaging system and consequently, food shelf life. In this work, an original experimental set-up was proposed to perform CO2 solubility measurement based on chemical titration of dissolved CO2. This methodology was adapted and used for monitoring CO2 diffusion in solid matrix as a function of the position in the food in order to obtain distribution profile of dissolved CO2 in the product. From these experimental profiles, accurate values of CO2 diffusivity could be then identified. This work takes place in the context of the MAP’OPT project (2011-2015), funded by the French National Research Agency, whose title is “Equilibrium gas composition in modified atmosphere packaging and food quality”