On the origin of primary aromatic amines in food packaging materials

Primary aromatic amines (PAAs) are substances that can be transferred from food packaging materials into foodstuffs and are "possibly carcinogenic to humans". The formation of PAAs from multilayer packaging materials consisting of aromatic polyurethane (PU) adhesives occurs from the reaction between residual isocyanic monomers that have migrated to the surface of the inner layer of the package and water molecules making contact with the same plastic surface. However, for foods subjected to thermal treatments, an alternative formation of PAAs should also be taken into consideration. Due to the detrimental effect of the temperature, some secondary bonds (namely allophanate and biuret bonds) displaced on the main PU backbone may be disrupted, originating neo-formed isocyanic monomers. The migration of these monomers from the adhesive layer across the inner sealing film can lead to PAAs as soon as they come into contact with the water molecules of the liquid or high aw packaged food. Although the existence and the mechanisms of the formation of allophanate and biuret linkages during the polymerization process with poly-isocyanates has been known for a long time, the negative impact on public health possibly arising from the migration of the neo-formed isocyanic monomers into the foods during thermal treatments seems to have not been fully perceived, with special regard to preservative heat treatments such as pasteurization and sterilization. In this viewpoint article, after covering both chemical and physical aspects involved in the formation of PAAs, especially in thermally-treated PUbased multilayer packaging materials, we have stressed the necessity for a more careful consideration of the risks associated with the potential formation of PAAs, in a first instance by strict compliance with the provisions included in the current European legislation. The necessity for alternative analytical tools for the PAAs quantification is also highlighted.