## 2 Materials and Methods  
### Sampling  
Seventeen dairy products packed in PS were purchased during 2021 from different Italian and German supermarkets. To avoid matrix interferences or styrene contamination from other origins as the PS packaging, only plain (natural) products, without addition of flavorings, spices, herbs, fruit, chocolate or other preparations, were selected. Products packed in PS of different brands were targeted, looking at the bottom of the pots for their labelling with the recycling code for PS = 6. Three stirred yogurts with fat content ranging from 0.1% to 4.4% were sampled in Italy. Three stirred yogurts with 3.5% fat content and four types of set yogurts with a fat content of 3.5-3.9%, as well the other dairy products, were sampled in Germany. The other dairy products were one sample of whipping cream (Schlagsahne) with 30% fat (fluid, not homogenized, with cream on top), one sample of solid sour cream (Schmand) with 24% fat, four samples of solid/semi-solid sour cream (Sauerrahm or saure Sahne) with 10% fat and one sample of UHT coffee creamers (Kaffesahne) with 10% fat. All of the samples (except for the coffee creamers) were refrigerated products and according to the information of the producers have an average shelf life of 40 days at 5 \({}^{\circ}\)C. The coffee creamers were UHT products stored at room temperature and have an average shelf life of 192 days. In Table 2, the food description and the main characteristics of the investigated products (packaging and content) are summarized. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Item/Country**} & **Food** & **Fat** & **Net** & **Packaging Description** & **Area Weight** & **S/F 1** \\  & **Description** & **Content [\%]** & **Content [g]** & **Packaging Description** & **[g dm\({}^{-2}\)]** & **[dm\({}^{2}\) kg\({}^{-1}\)]** \\ \hline \multicolumn{8}{c}{Refrigerated products (Shelf life: 40 days/5 \({}^{\circ}\)C)} \\ \hline \multirow{2}{*}{1 Italy} & Stirred, creamy & \multirow{2}{*}{4.4} & \multirow{2}{*}{125} & PS pot-No labels/no printing & \multirow{2}{*}{3.58} & \multirow{2}{*}{11.0} \\  & yogurt & & & & & \\ \multirow{2}{*}{2 Italy} & Stirred, sugared & \multirow{2}{*}{3.2} & \multirow{2}{*}{125} & PS pot-Outside printed & \multirow{2}{*}{3.29} & \multirow{2}{*}{11.4} \\  & yogurt & & & & & \\ \multirow{2}{*}{3 Italy} & Stirred, light & \multirow{2}{*}{0.1} & \multirow{2}{*}{125} & PS pot-No labels/no printing & \multirow{2}{*}{3.78} & \multirow{2}{*}{10.6} \\ \cline{1-1}  & yogurt & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Description and main characteristics of the investigated products (food and packaging). Determination of the Migration Levels of Styrene in Yogurt/Dairy Products from the Market by Purge & Trap Gas Chromatography Analysis  
After buying in the supermarket, the samples were stored cooled in a refrigerator at 5 \({}^{\circ}\)C (except for the coffee creamers that are UHT products and not refrigerated at retail level which were stored at room temperature). At the best before date (BBD) of each sample (as reported on each product from the producer), the pots were opened, each yogurt/dairy product was stirred, and 1 g was weighted in glass vials) which were frozen until analysis (triplicate per sample). Some of the samples were additionally investigated approx. 20 days before and 15 days after the indicated BBD. In the case of the multipack, analyses at different dates were performed using the different portion; in the case of single selling unit, to perform analyses at different dates more products were bought. For analysis, 5 mL of freshly boiled and cooled down water (HPLC grade) and 10 \(\upmu\)L of an internal standard solution 4.52 ppm of m-xylene were added to each sample after defrosting and shaken for approximately 2 h using a flat bad shaker.