Food Packaging Innovations- Electrochemical Nanosensors far Primary Aromatic Amines Quantification

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 (the most widely used of which are 2,4-toluene diisocyanate – TDI and 4,4’-methylene diphenyl diisocyanate – MDI) 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 (such as TDI and MDI). 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. Regardless of the origin, the quantification of the risks associated with the potential formation of PAAs must be made by strict compliance with the provisions included in the current European legislation. However, both the non-selectivity of the widely adopted spectrophotometric method and the number of drawbacks associated with the more sophisticated techniques used at academic level and highly specialized laboratories impose the necessity for alternative analytical tools for the PAAs quantification. In this thesis, after an introductive part on electrochemistry and the use of electrochemical sensors in food science, an in-depth review of the issues associated to the PAAs migration possibly occurring from food packaging materials is presented in chapter 1. In the following three chapters, the focus has been addressed to the implementation of electrochemical routes for the determination of PAAs by the development of modified electrochemical sensors characterized by high selectivity and sensitivity. More specifically, chapter 2 deals with the fabrication of a modified glassy carbon electrode (GCE) for the selective quantification of TDA. Different levels of complexity were investigated by modifying the electrode’s surface with multi-walled carbon nanotubes (MWCNTs), MWCNTs in chitosan (CS) and using gold nanoparticles (AuNPs). In chapter 3 is described the development of a nanosensor for the MDA determination using multi-walled carbon nanotubes, chitosan, and gold nanoparticles for the modification of a glassy carbon electrode (MWCNTs-CS-Au/GCE). In chapter 4, a new electrochemical sensor is proposed to determine MDA using a templating-based method known as ‘molecularly imprinted polymer’, together with multi-walled carbon nanotubes as conductive nanoparticles (MIP/MWCNTs/GCE). The three electrochemical sensors have been described in detailed fashion as far as both a polymer science perspective and analytical performance are concerned.