A large amount of research has been conducted into the migration of contaminants and toxic additives from plastic packaging materials into food and food simulants (Brede et al., 2002). Estimates of the exposure to contaminants in the diet are determined by combining migration data with information on the uses of food packaging that may contain additives or contaminants (Simoneau et al., 1999). Traditionally, migration data are obtained from tests in which plastics are brought into contact with a food simulant (e.g., vegetable oil, alcoholic or acidic solution) under established time and temperature limits (Commission Directive 97/48/EC, Council Directive 85/ 572/EEC).
The European Commission has mandated the European Committee for Standardization to establish a validated method of analysis for the determination of OMLs and SMLs. If a product complies with the compositional requirements of the directives, i.e., it is produced from authorized monomers and additives, then it may be tested for any desired application. If it meets the migration requirements, it is acceptable for use in cases covered by that test method. Typical food simulants used in the tests are hot water, acetic acid, ethyl alcohol and olive oil. The choice of an appropriate simulant depends on the type of food expected to come into contact with the packaging.
Analysis of migrants in a foodstuff or simulant may be very expensive, time-consuming and complicated because of the low concentrations of migrating substances in the foods and the complexity of the matrix. To overcome these difficulties, migration evaluation procedures based on theoretical prediction of migration from plastic food-contact material were recently introduced. Using data from migration studies under controlled conditions it is possible to establish mathematical models of the migration process specific to different food-contact materials and foods. Such models are indispensable in the prediction of the extent of migration, and could be crucial for helping regulatory authority to set up guidelines regarding the use of food-contact materials (Baner et al., 1996; Begley 1997; Lau and Wong 1997; Helmroth at al., 2002). The rate and extent of migration are mainly affected by the properties listed in Table 14.4.
The process of migration of additives or contaminants from polymeric food packaging to food may be separated into three stages: diffusion within the polymer, solvation at the polymer-food interface, and dispersion into bulk food.
The rate of migration of additives or contaminants is controlled primarily by diffusion within the polymer lattice. Because the migrants pass through voids and other gaps between the polymer molecules, the migration rate depends on the size and shape of the migrants and on the size and number of the gaps. It also depends on polymer's properties, such as density, crystalinity, and degree of crosslinking and branching. The glass transition temperature (Tg) of the polymer, which determines the flexibility of the polymer molecules, is also important. Below Tg, the polymer molecules are stiff (glassy state) and
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