Mass transfer in food/plastic packaging systems

The packaging of foods is one of the major factors involved in food preservation. Packages are designed to meet the special requirements of each specific product. Many variables take part in the design (size, shape, etc.), but none is so important as the materials. In the last third of the twentieth century, plastics have been used in the packaging of many food products. They are utilized as an alternative to traditional paper, glass, and metal containers, and they have been present in the development of new products along with food technology industries. The continuous increase in plastic packaging applications is due to some attractive properties such as low cost, easy manufacture, low weight, versatility in size and shape, and a wide range of mechanical properties. However, plastic materials do allow mass transport of low molecular weight due to their peculiar morphology. Substances such as permanent gases, water vapor, food aroma components, odors, plastic residues, and additives are exchanged within the environment/package/food system. Such exchange processes are commonly called permeation, migration, and sorption. Due to the effect that mass transport has in food quality, many studies have been focused on the characterization and understanding of the process involved. In this chapter, we will introduce mass transport mechanisms, factors affecting its extent and kinetics, how they can be controlled and used in the design of a product package, and the beneficial effects that can be obtained from permeation, migration, and sorption in the preservation of food products.