Food packaging is primarily intended to protect the food contained in the packaging from temperature and atmospheric changes, oxygen, dust and moisture, as well as increase its shelf life, or the maximum length of time a particular food remains fresh and safe for consumption.

Food products are protected from alterations or external impacts by their packaging. Food and packaging may alter each other by direct contact. Thus, substances from food may migrate into the packaging but also vice versa. Already during production of packaging material, migration is therefore an important issue. Components like photo initiators, adhesives, films or barrier coatings may leave undesired substances on the packaging and as a result in food.

For the protection of consumers, migration of substances which have an impact on health or quality of the food has to be ruled out. Therefore in regulation 10/2011 (PIM) restrictions for plastic materials and objects are laid down. As long as the food is not packed yet, testing is carried out under worst case contact conditions with food stimulants reflecting the properties of the food to be packed.

The sum of all migrated substances – global migration – must not exceed the limit of 10 mg per dm2 area of packaging material. In addition there are specific migration limits (SML) for certain substances which define the maximum limits in food.

What is migration?

In the context of food contact materials, migration means the transfer of substances from packaging materials into food. Note that migrating substances can potentially come from packaging substrates, such as for example paper, board or plastics, as well as from packaging components like adhesives, printing inks or coatings used to make up the overall package. It is therefore important to consider the overall packaging material or article.

Types of migration:

Migration can occur in a number of different ways:

Contact migration – involves the direct transfer of substances from the food contact surface of the packaging into the food. Examples might include the transfer of substances from a cardboard pizza box to the underside of a pizza, or transfer of substances from a plastic tub, tray, pouch or wrapping into food.

Gas phase migration – involves the transfer of volatile substances through the airspace between food and packaging and into the food by the process of diffusion. A good example might be the diffusion of mineral oil from recycled paper-board, into solid dry foodstuffs. Note that in this case, mineral oil can potentially migrate from the cartons, through an airspace, through a plastic inner pouch (subject to its barrier properties) and through a second airspace into the food.

Penetration migration – involves the transfer of substances from the nonfood contact (often printed or coated) surface of the product’s packaging, through the substrate and onto the food contact side of the packaging. Once on the food contact surface, the migrating substances can be transferred to the food by either contact or gas phase migration.

Set-off migration – involves the transfer of substances from printing inks, coatings or varnishes from the printed, nonfood contact side of the packaging to the food contact side, as a result of the stacking of printed items e.g. carton flats, or when winding a printed film into a reel. Note that set-off migration may be either visible or invisible. Once on the food contact surface, substances arising through set-off can be transferred to the food by either contact or gas phase migration.

Condensation / distillation migration – involves the transfer of substances into food during heating processes such as sterilization or boiling of e.g. pouched food, or oven / microwave cooking of food in cartons or trays. It involves the evaporation of volatile components from the packaging and by steam distillation in the case of moist / aqueous foods

Factors affecting migration:

The rate of migration is affected by a large number of factors:

Molecular size of the migrant – generally speaking small molecules migrate faster than larger ones. As a rule of thumb, substances with a molecular weight of greater than 1000 Daltons are deemed too large to migrate to any significant degree. (E.g. Benzophenone is a much smaller molecule)

Temperature – since migration occurs through physico-chemical processes, it significantly increases with increasing temperature. Typically, little appreciable migration occurs under frozen conditions, other factors may still apply and affect migration activity, such as humidity. Note that both storage and processing, including cooking, temperatures need to be considered.

Time – migration is time dependent. A food package which is compliant at the beginning of its shelf life could be non-compliant by the end of its life. (E.g. long-life ambient product)

Nature / composition of the food – e.g. liquid or solid? Aqueous or fatty? Moisture / fat content? Granular? Particulate? Surface area? Note that fatty foods will tend to attract non-polar migrants, while water-based foods will tend to attract polar migrants. Foods with a high surface area to volume ratio are typically more susceptible to migration. (E.g. high surface area – pasta)

Nature / structure of the packaging – different substrates differ in their permeability to potential migrants. Metal and glass are considered to be absolute barriers to migration. However, migration from metal containers into foods that may degrade the food contact surface should be considered as well as migration from coatings. The rate of migration through (e.g. plastic films and aluminum foils) will depend on thickness, density and chemical make-up. In technical terms the rate of migration will be determined by diffusion coefficients. Note that a given film may be a reasonable barrier to one potential migrant while presenting virtually no barrier to a chemically different migrant. (E.g. multilayer materials used as barrier to multiple substances.) Please see later for a discussion / definition of “functional barriers”.

Amount of migrate able substance in the packaging – in the case of substances migrating from printing inks, coatings, varnishes or adhesives, this will relate to both the amount of migrant present in the ink / coating or adhesive and the weight of the ink, coating, varnish or adhesive applied. It is not inconceivable that the same potential migrant could be present in several of the components of the package, for example in a printing ink applied to a carton, in a plastic inner pouch and in an adhesive used to seal the carton (e.g. bag in box). Therefore all components of a particular package need to be considered.

Ratio between packaging surface area and volume (weight) of packaged food – the greater the packaging surface area in relation to the weight of food, the greater will be the impact of any potential migration. For example, the impact of migration into an individual portion of butter would be proportionately greater than into a catering pack packaged in the same materials due to the higher ratio of packaging per gram of product.

Application and testing

When a product is to be tested, the intended use of the product is taken into account. A plastic whisky, for instance, will not be tested under equal conditions as a plastic marmalade pot, because contact time and temperature shall both be taken into consideration in the test arrangement.

A whisky must meet the requirements for migration during short-time exposure to elevated temperatures, whereas a pot for e.g. marmalade shall store the foodstuff at low temperatures for a longer period.

When arranging the proper test conditions, we need Regulation 10/2011/EC and subsequent amendments. The regulation contains tables that specify the test duration for different contact duration.

The directive also provides tables of contact temperatures, thus ensuring that the product is tested at the maximum temperatures it will be exposed to. Consequently, the expected use of an article must be assessed as realistically as possible when setting up testing schemes – and a “worst case” scenario must be chosen as well. If a product can be used, for example, at both ambient temperature and in the refrigerator, the test will always be conducted at the highest temperature. Thus, the results will also be applicable for the lower temperature scenario.

Why testing of  food contact material important?

Food contact material testing is an essential requirement to gain legal access to important consumer markets. In addition, major global retailers may mandate certain additional testing for food packaging and contact materials as part of their procurement requirements, further validating the importance of food contact material testing.

http://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX%3A32011R0010