Migration from plastic food packaging during microwave heating
Abstract: Microwave heating of food has increased rapidly as a food processing technique. This increases the concern that chemicals could migrate from food packaging to food. The specific effect of microwave heating in contrast to conventional heating on overall and specific migration from common plastic food storage boxes was studied in this work. The purpose was especially to determine the interaction effects of different plastics in contact with different types of foods during microwave heating. The study focused on polycarbonate (PC), poly(ethylene terephthalate) (PET), polypropylene homo-polymer (PP), co-polymer (PP-C) and random co-polymer (PP-R) packages. The migration determinations were evaluated at controlled times and temperatures, using a MAE device. The migrants were analyzed by GC-MS and HPLC. ESI-MS was evaluated as a new tool for migration determinations. Food/food simulant absorption and changes in degree of crystallinity during heating were also followed.Significant degradation of antioxidants Irgafos 168 and Irganox 1010 in PP packages occurred during microwave heating of the packages in food simulants containing ethanol, resulting in the formation of antioxidant degradation products. Degradation of PC by Fries chain rearrangement reaction leading to formation of 9,9-dimethylxanthene, and transesterification of PET leading to formation of diethyl terephthalate, were also observed after microwave heating the packages in ethanol and 90/10 isooctane/ethanol. These reactions were not observed during conventional heating of the packages at the same temperature, or after microwave heating of the packages in liquid food (coconut milk). The microwave heating also significantly increased the migration of cyclic oligomers from PET into ethanol and isooctane at 80 °C. Migration of compounds into coconut milk was slightly lower than calculated amounts using the EU mathematical model to predict migration of additives into foodstuffs. The results thus show that the use of ethanol as a fat food simulant during microwave heating can lead to a significant overestimation of migration as well as degradation of polymer or the incorporated additives.Some other detected migrants were dimethylbenzaldehyde, 4-ethoxy-ethyl benzoate, benzophenone, m-tert-butyl phenol and 1-methylnaphthalene. All identified migrants with associated specific migration limit (SML) values migrated in significantly lower amounts than the SML values during 1 h of microwave heating at 80 °C. The antioxidant diffusion coefficients in PP and PP co-polymers showed larger relative differences than the corresponding degrees of crystallinity in the same polymers and PP-R showed by far the fastest migration of antioxidants.
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