Cross-linked polyester resins are being introduced into the market as alternatives to epoxy resins as coatings for metal food cans. Identification of potential migrants, from these coatings into food, is a significant analytical challenge due to the diversity of substances employed in the manufacture of the coatings. However, such identification is required to assess migration from the can coating into the food and quantify dietary exposure. Polyester can coatings were extracted with acetonitrile at 40°C for 24h and the extracts were analyzed by a variety of analytical techniques, including GC-MS, HPLC-DAD/MS, HPLC-DAD/CAD and UHPL C-HRMS. Twenty nine non-volatile oligomers were tentatively identified using retention times, UV spectra, and accurate mass measurements. Identified oligomers suggest the coating in use for food cans is a polyester coating and is mainly based on the monomers isophthalic acid, terephthalic acid and nadic acid. To give confidence in the identification, one of the tentatively identified oligomer was synthetized and analyzed by (13)C and (1)H NMR and UHPL C-HRMS. The NMR and HRMS results, confirmed the presence of this compound in the can extracts. Finally, to determine if rapid, direct detection of the oligomers was practical, the coatings were analyzed by DART-HRMS. Twenty three out of the 29 oligomers were identified in the coating by direct measurement with DART-HRMS in few minutes.

Traditionally, migration testing during 10 days at 40 °C has been considered sufficient and appropriate for simulating the potential migration of substances from food-contact materials into foods. However, some packages, such as food cans, may be stored holding food for extended time periods (years). This study attempts to verify whether common testing conditions accurately estimate long-term migration. Two types of can coatings, epoxy and acrylic-phenolic, were subjected to short-term and long-term migration testing (1 day-1.5 years) using food simulants (water, 3% acetic acid, 50% ethanol, and isooctane) at 40 °C. Using HPLC-DAD/CAD, HPLC-MS, UHPLC-HRMS (where HRMS is accurate mass, mass spectrometry), and DART-HRMS, we identified potential migrants before starting the experiment: BPA, BADGE, BADGE derivatives, benzoguanamine, and other relevant marker compounds. During the experiment using a water-based food simulant, migrants remained stable. Most of the cans in contact with 3% acetic acid did not survive the experimental conditions. Tracked migrants were not detected in isooctane. In the presence of 50% ethanol, the traditional migration test during 10 days at 40 °C did not predict migration during long-term storage. These results suggest that migration protocols should be modified to account for long-term storage.

FDA guidance for food contact substances recommends that for food packaging intended for use at sterilized, high temperature processed, or retorted conditions, a migration test with a retort step at 121 °C for 2 h followed by a 10 day migration test at 40 °C should be performed. These conditions are in intended to simulate processing and long-term storage. However, can coatings may be in contact with food for years, and there are very few data evaluating if this short-term testing accurately simulates migration over extended time periods. A long-term migration test at 40 °C with retorted and non-retorted polyester cans using several food simulants (water, 3% acetic acid, 10% ethanol, 50% ethanol, and isooctane) was conducted to verify whether traditional migration testing protocols accurately predict migration from food contact materials used for extended time periods. Time points were from 1 day to 515 days. HPLC-MS/MS was used to analyze polyester monomers, and oligomer migration was monitored using HPLC-DAD/CAD and HPLC-MS. Concentrations of monomers and oligomers increased during the migration experiments, especially in ethanol food simulants. The data suggest that current FDA migration protocols may need to be modified to address changes in migrants as a result of long-term storage conditions.