## 4 Discussion
We found in our investigation on real dairy products taken from the market that the ratio between the PS surface contact area of the package and the quantity of the food packed (S/F), the time/temperature conditions of production/packaging filling as well as of storage/shelf life of the products are the main factors influencing migration of styrene monomer into real foods taken from the market. With the limited data available to date, it can be shown that actual migration of styrene into refrigerated dairy products (real products taken from the market) is generally much lower as obtained in the corresponding food simulant (50% ethanol) under standardized condition. Indeed, migration from HIPS was recently investigated, testing extruded sheets by total immersion under the standardized conditions 10 days/40 \({}^{\circ}\)C (which are laid down in the EU legislation to simulate all storage times at refrigerated and frozen conditions including hot-fill) with the food simulants 50% ethanol (simulant for dairy products) [27]. Styrene migration under these conditions reached 297 ug/kg in 50% ethanol (calculated applying a surface/volume ratio of 6 dm\({}^{2}\)/kg), which corresponded to a relative migration of approx. 7%. Swelling (uptake of liquid by the PS polymer due to interactions with ethanol) reached 1.3%, which was considered the cause of exaggerated migration values. Within the same study, styrene levels of 152 ug/kg (3.6% relative migration) and 278 ug/kg (6.6% relative migration) were determined, respectively, in milk (3.5% fat) and cream (30%fat) tested by total immersion at 10 days/40 \({}^{\circ}\)C. Swelling with real foods was not observed. Migration in these foods, tested at 40 \({}^{\circ}\)C by total immersion, was much higher than in the refrigerated milk products taken from the market which were investigated within the present study. The higher temperature increases the migration rate strongly; the test specimen edges in contact with the media (food or food simulant) might also affect the styrene migration behavior. The highest styrene migration level found with the present study in the refrigerated dairy products (yogurts and creams packed in PS) taken from the market was 30 \(\upmu\)g/kg, which is approx. ten times lower as found migrating from HIPS sheets in 50% ethanol, tested at 10 days/40 \({}^{\circ}\)C by total immersion. On the other hand, styrene levels in the coffee creamers in PS single portions which were UHT products stored at room temperature for approx. 6 months with a surface to volume ratio (S/F) of 28 dm\({}^{2}\)/kg were determined at BBD equal to 401 \(\upmu\)g/kg. In our previous study [27], styrene migration from HIPS sheets was determined in 50% ethanol tested by total immersion at 10 days/60 \({}^{\circ}\)C (prescribed time/temperature condition in the EU legislation to simulate contact times longer than 30 days at room temperature and below) equal to 341 \(\upmu\)g/kg, calculated applying a surface/volume ratio of 6 dm\({}^{2}\)/kg (according to the EU cube model). This concentration of styrene can be recalculated using a S/F ratio of 28 dm\({}^{2}\)/kg (for simulating the application: single serving coffee creamer) instead of the conventional ratio of 6 dm\({}^{2}\)/kg equal to 1591 \(\upmu\)g/kg. In the light of the above mentioned, it is possible to conclude that migration tests applied within laboratory simulations with 50% ethanol to evaluate regulatory compliance appear too severe and are not representative for the majority of the real food packaging application of PS, which are mostly refrigerated dairy products (such as yogurt and cream) with single side contact and a shelf-life of approx. 40 days. Additionally, it has to be considered that the S/F ratio values of dairy products packed in PS mainly differs from the EU standard ratio of 6 dm\({}^{2}\)/kg, especially in the case of small plastic packages (such as single serving applications). This conventional S/F ratio shall compensate for the smaller amount of food consumed from such small packages.