Food migration testing for food contact materials

M. Ossberger manfred.ossberger@fabes-online.de    FABES Forschungs-GmbH, Munich, Bavaria, Germany

1.1 Introduction

The demands on packaging materials are an image of human history. In early times food was consumed where it was found. Where transportation of (liquid) food was necessary, nature provided animal skins or shell-like gourds, coconuts, or large plants. Later, baskets were constructed from stiff grasses or reeds and were used for food storage and its transportation. First improvements included using ceramics in the Middle East and making sacks of networks or fabrics; glass containers manufactured by the Aegypts led not only to better durability but also to better protection of the food against spoilage, insects, and microorganisms. Wooden barrels were created by the Gauls, which were better suited than the use of amphorae out of ceramics to the increasing goods traffic; barrels were an improvement in supporting the weight of packaging material, storage, and the distribution of the packaging material including food. Food durability was decisively improved by the invention of heat sterilisation of food contained in glass containers by the Frenchman Appert in the early nineteenth century. This improvement was highly welcomed not only by Napoleon for military reasons, but also for the expansion of trade and any situation in which eatable food had to be stored for a very long time (Paine and Paine, 1993, p. 1). Until this point, only such preservation techniques as drying, salting, and smoking were known. These stages document the long struggle against microorganisms such as bacteria and fungi. Swift population growths coupled with higher goods traffic followed new solutions in the packaging sector. More freedom and individualisation of the population followed the inventions of the large new varieties of packaging materials and their marketing. New functions of the packaging, including environmental compatibility and consumer convenience, have and will lead to new solutions of packaging materials such as paper and paperboard, aluminium, and collapsible, soft metal tube packaging materials (Berger, 2002; Welt, reviewed 2005). Nevertheless, when new materials are introduced to the market consumer health problems can arise, for example, the use of lead in soldering tin containers led to lead poisoning. The ‘newcomer’ on the market, plastic, which has pushed back glass as a primary material, is a good example how close the pros and cons can be. Glass has the major advantages of ‘no migration’ properties and recyclability. By ‘migration’ we mean the diffusion of substances from food contact material into the food, which can be of risk to human health or vice versa, which is important to the quality of the food. Permeation refers to the process where chemical substances diffuse, such as through a certain layer of a multilayer material or vice versa. It is common to describe the mass transfer process as ‘migration’. In contrast, plastics, which are polymers including additives, can be easily adjusted to an optimum functionality and protection of the food and to fit a huge variety of customer needs. A disadvantage to plastics is that only a fraction of used plastics are recycled and plastic components including residual monomers or solvents, production aids, additives, and by-products are able to migrate from the mono- or multilayer plastic material into the foodstuff. This could lead to higher toxicological risk to the consumer, and hence plastics have to be risk-assessed. For consumer protection, we need to post recommendations, legal directions, and regulations on a national and international basis, including lists of substances that may be used in the manufacture of food contact materials. The use of these substances could be restricted by limits to migration or limits of initial concentration. One possible way to proof conformity of the material is to measure the migration by analytical methods and compare the result with the migration limit. Details on the procedure of migration tests are well defined in the case of plastic material regulation. Although, it is important to mention, it is common to use simulants instead of real foodstuff; for example, the food simulant for milk is 50% ethanol. The reason is the complicated matrix of real foodstuff, which allows no cheap standard in screenings and specific measurements. On the other hand, only small changes of the food matrix can lead to different and less comparable results. In summary, huge efforts have to be made to understand diffusion processes from food contact materials such as plastics and paper and boards and to control and estimate their risk to human health.

In the next chapters, we explain different analysis techniques, which are important in the field of migration measurement. We present several published migration investigations and summarise and the results.

1.2 Possibilities of food migration testing

In principle there are two possibilities for migration testing. On the one hand is the analytical option of using laboratory equipment; on the other hand it is possible to apply a simple calculator or software programme to calculate the migration of specific substances under certain terms. In this chapter we present the preparation of migration solutions, principles, and methods of separation and detection of migrants and their quantification.

1.2.1 Preparation of migration solution

The first step in migration testing is the preparation of migration solutions. There are several possibilities. The method most frequently used is the ‘one side migration test’ in which the tester cuts a circular sample out of the test sample, fixes it in a glass, steel, or aluminium cell (DIN EN 1186; DIN EN 13130-1), and brings the food contact side into contact with simulants or food at specific time and temperature conditions. Figure 1.1 shows an example for glass cells. When a test sample is a monolayer material, the tester has the option to totally immerse the sample in the food or simulants in the glass cell (two side migration test). In this case both sides can be calculated as contact areas when the material has the minimum thickness of 500 μm (Food and Drug Administration, 2007). Containers such as cups can be filled directly with simulants and stored in closed conditions at specific temperatures. Another possibility is to prepare pouches of the contact material and fill the pouches with these simulants (DIN EN 1186; DIN EN 13130-1). After certain migration conditions, which depend on the real use of the material, the migrant in the migration solution is analysed either directly without further preparation or after evaporation of the solution to, for example, 1–2 ml. With regard to dry foodstuff, Tenax® (modified polyphenylene oxide, MPPO) is used as a simulant and has to be extracted with a solvent before further analysis.

1.2.2 Measurement of migrants

1.2.2.1 Specific determination

The kind of analysis that has to be performed on the migration solution depends on the question. If a specific determination of the migration of a substance is necessary, then a specific method including calibration curves have to be established. External calibration curves are built up by injecting standard solutions with a different concentration of the substance, which is then analysed. The migration solution itself is also injected. The corresponding signal and the calibration curve lead to the concentration of the specific substance in the migration solution, as displayed in Figure 1.2. In general, all chromatographic detectors produce a peak as a signal, and the area of this peak is proportional to the concentration of a specific substance. No detector responds equally to different compounds. As the response factor of the detector (sensitivity) may change at different concentrations of substances, the calibration curve deviates from the ideal linear relationship to a curve. The relative response factor (Rfrel) is defined as follows:

frel=Aa⋅cstdAstd⋅ca

Aa = peak area of analyte

Astd = peak area of internal standard

ca = concentration of analyte

cstd = concentration of internal standard