Crosslinking in polysaccharide and protein films and coatings for food contact – A review

Crosslinking is the process of forming tridimensional networks by linking polymer chains by covalent or noncovalent bonds. It is useful for polysaccharide- and protein-based films and coatings to be applied to food surfaces, enhancing their water resistance as well as mechanical and barrier properties. Crosslinkers intended to be used for food contact materials must present low toxicity. This review is a summary of the main crosslinking agents which have been used for protein and polysaccharide films and coatings, and which may be applied as food contact materials. The study emphasizes the mechanisms of crosslinking agents, the chemical groups involved, conditions for application, advantages and drawbacks, as well as examples of applications for food contact materials. Crosslinking is a promising technique to improve the performance and applicability of protein- and polysaccharide-based food contact materials, especially concerning their water sensitivity, which hinders many of their potential applications as food contact materials. Some aldehydes are very effective as crosslinkers, but they have been avoided in food contact materials because of possible migration of aldehyde residues to food, and less toxic compounds have been studied for those applications, such as phenolic acids, oxidized polysaccharides, and enzymes. Crosslinking techniques may help make protein- and polysaccharide-based materials more suitable for large-scale processing and applications in the future.