Theoretical Study of the Release and Consumption of an Agent in Food from Active Polymer Packaging

Abstract

The role of packaging has been extended from passive protection to an active role in improving food quality. Active packaging works with the food to produce a desired effect. Often, micro-organism growth causes food spoilage, so active packaging allows for the controlled release of an anti-microbial agent into the food. Thus, packaging is made of two layers, at least, one with an impermeable polymer protecting the system from the environment, and the other with a polymer carrier containing the agent, the polymer carrier being bound to the inside of the packaging and in contact with the food. This study is undertaken in order to describe the process of the agent release. The agent diffuses through the polymer carrier with a constant diffusivity into the liquid food, with a finite coefficient of convective transfer at the interface. Because of the high convective effect in the liquid, the concentration of the agent in the liquid food is uniform. Moreover, the rate of consumption of the agent resulting from its action on the micro-organisms is controlled by a first-order reaction with respect to its concentration in the liquid. The results are expressed in terms of the profiles of concentration of the agent developed through the thickness of the polymer carrier, the kinetics of the agent remaining free in the liquid, and the kinetics of consumption of the anti-microbial agent by the microorganisms. Two new dimensionless numbers are introduced, taking into account the rate of consumption of the agent and either the diffusivity, when the process is controlled by diffusion, or the rate of convection coefficient when it is controlled by convection, in order to clarify the process an help those who are not specialists in modelling.