In an article published on March 7, 2022, in the journal Talanta, Julien Terrasse from the Université de Lyon, France, and co-authors analyzed non-intentionally added substances (NIAS) extracted from polyester-phenolic can coatings and the influence of the phenolic resole used in the formulation on the nature of NIAS. Phenolic resins that are based on phenol and alkylated phenol resoles are added to internal coatings of food contact metal cans as cross-linking agents with resoles being the most frequently used phenolic resin in that type of application. Resoles are synthesized by a base-catalyzed condensation of phenols with formaldehyde.
The scientists prepared six different polyester coatings using either a phenol, cresol, or tertbutyl phenol-based phenolic resins in each of them. Subsequently, coatings were applied to plates, cured, and coated films were extracted for 24 h at 40 °C using acetonitrile. Terrasse and co-authors conducted non-targeted gas chromatography (GC) coupled to high-resolution mass spectrometry (HRMS), which they used to identify the extracted NIAS along with theoretical databases and nuclear magnetic resonance (NMR) spectroscopy analyses. Non-targeted screenings of chemicals migrating from canned products are currently lacking (FPF reported).
Terrasse et al. identified two groups of NIAS in the extracts: (i) cyclic polyester oligomers present in all extracts and whose quantities were not influenced by the type of resole, and (ii) specific NIAS which were only detected in tertbutyl phenol-based resoles. Aldehyde compounds were the most abundant NIAS and were found to be “directly present in the native resole as side-products of their production process and not produced within the formulation or the cure of the coating.” The authors emphasized that they were the first to identify these aldehydes in food contact materials. Future studies are recommended to test commercially available can coatings via migration experiments to verify the presence of these new NIAS in products and to estimate their quantity of exposure in a real-world situation.
Polyester coatings are frequently used as alternatives to bisphenol A containing epoxy-based coatings. Previous studies have reported oligomer migration from polyester coatings after long-term storage and suggested a modification of standard testing protocols (FPF reported and here).
Reference
Terrasse, J. et al. (2022). “Non-targeted screening of extracts from polyester-phenolic can coatings: Identification of new aldehyde molecules from resole-based resins.” Talanta. DOI: 10.1016/j.talanta.2022.123351
