In a new study published online on January 8, 2015 in the peer-reviewed journal Food Additives & Contaminants: Part A, researchers from the U.S. Food and Drug Administration (FDA) investigate the effectiveness of functional barrier layers in colored polystyrene bowls (Genualdi et al. 2015). Functional barriers in food contact materials (FCMs) prevent or reduce chemical migration from inner layers in multilayer structures to food. Unregulated substances are allowed in the inner layers of the laminate, but they may potentially migrate to food through disrupted barrier layers. Thus, unapproved and untested food additives might be transferred into the food, which is then considered adulterated under the Federal Food Drug and Cosmetic Act. Polystyrene (PS) is used in the manufacture of FCM articles such as disposable kitchenware or trays for meat. Bright colors of these products are often induced using solvent dyes. Some dyes used in the colouring of PS are not allowed in food contact due to their toxic and carcinogenic properties. The presence of any barrier layer preventing migration is critical in such products to avoid dye migration into the food. The new study assesses the effectiveness of a virgin PS barrier layer in colored disposable products. Genualdi and colleagues investigated migration of solvent dyes from colored PS bowls and examined structural changes in the FCM due to its interaction with food simulants.
Materials and methods
Migration experiments were performed over 10 days. FDA recommended food simulants ethanol, corn oil, and Miglyol 812® (a neutral oil) were used along with several other food oils. At day 10, solvent dyes were separated from the food simulants and analyzed using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). To identify other components of the PS bowls, which might contribute to the release of solvent dyes, bowls were extracted and analyzed using gas chromatography–mass spectrometry (GC-MS). To determine whether or not the PS barrier layer was still intact scanning electron microscopy (SEM) was used to compare samples of PS bowls before and after exposure to food simulants. Further, to assess whether or not the migration oil and temperature conditions resulted in structural changes of the PS bowls, differential scanning calorimetry (DSC) was used. Finally, Migratest©Exp software was used to simulate the diffusion of the solvent dye within the multi-layer structure and its migration into food.
Results and discussion
Palm kernel oil, coconut oil and Miglyol. At the end of the 10-day period, solvent dyes migrated from the PS bowls at 1, 12, and 31,000 ng/cm2 into palm kernel oil, coconut oil and Miglyol, respectively. In all other food simulants, concentrations detected were below the method detection limit. The PS bowl exposed to Miglyol was visibly bleached and the food simulant itself changed color. Color change was also observed for coconut oil. Overall, only the food simulants composed mainly of saturated medium chain fatty acids showed migration of the solvent dyes. Therefore, it seems that these compounds have a more pronounced adverse effect on the PS barrier layer in comparison to the other food simulants. SEM images showed that the functional barrier was no longer intact for the bowls that were exposed to coconut oil, palm kernel oil and Miglyol. For the latter, the inner layer was completely saturated and the oil was appearing as a part of the inner structure. It was further investigated whether or not the short-chain fatty acids in Miglyol, coconut oil, and palm kernel oil dissolved the PS barrier layer in the bowls. The results show that solubility was, however, not responsible for the loss of the functional barrier layer and, therefore, further testing on the polymer was performed. GC-MS analysis of the PS bowls revealed that they contained on average 11 mg/kg of 1-dodecanol. This substance was likely used as a dispersing agent allowing the dye molecules to be homogeneously dispersed in the bowl and it possibly enhanced the migration of the dyes from the bowls into Miglyol, coconut oil and palm kernel oil.
Ethanol and goat’s milk. For 10% ethanol, 50% ethanol and goat’s milk, the loss of a virgin PS barrier layer was also observed after 10 days. However, no solvent dyes were measured in these three food simulants, most likely because the dyes were not soluble in aqueous solutions.
Thickness of the barrier layer. Finally, simulation experiments showed that the 40 μm barrier layer was not sufficient to prevent migration of the solvent dye to food. However, when the barrier layer thickness was increased to 60 μm, 80 μm, and 100 μm, the layer remained contaminated up to approximately 60 μm, but only negligible, if any, migration to the food occurred.
The authors have not provided any final recommendations regarding the suitability of virgin polystyrene as a functional barrier layer in colored FCMs.
Genualdi, S. et al. (2015). “Investigation into the suitability of polystyrene as a functional barrier layer in coloured food contact materials.” Food Additives & Contaminants: Part A (published online January 8, 2015).