Most food packaging systems represent either a package/food system or a
package/headspace/food system (Fig. 1.1). A package/food system is a solid food product in
contact with the packaging material, or a low-viscosity or liquid food without headspace.
Diffusion between the packaging material and the food and partitioning at the interface are the
main migration phenomena involved in this system. Antimicrobial agents may be
incorporated into the packaging materials initially and migrate into the food through diffusion
and partitioning (Han, 2000). Package/headspace/food systems are represented by foods
packed in flexible packages, cups, and cartons. Evaporation or equilibrated distribution of a
substance among the headspace, packaging material and/or food has to be considered as a part
of main migration mechanisms to estimate the interfacial distribution of the substance. A
volatile active substance can be used in these systems, as it can migrate through the headspace
and air gaps between the package and the food.