How to monitor the protein cross-linking by formaldehyde, glutaraldehyde or glyoxal in cotton-seed protein protein-based films? (short communication)

Abstract

Cotton-seed protein-based films can be formed from an aqueous solution by a casting process. Chemical cross-linking treatments of cotton-seed proteins by dialdehyde increased maximum puncture force and decreased solubility of films in water. Glutaraldehyde, formaldehyde and glyoxal are cross-linking agents capable of reacting with amino acid side chains, particularly with the lysine ENH2 group, to form Schiff bases. As a first approach, simple criteria (maximum puncture force, puncture deformation, and film solubility) were used to assess the efficiency of chemical treatments. In the present study the amount of lysine that did not react with cross-linking agents (reactive lysine) during cotton-seed protein film formation was used to assess the degree of protein cross-linking. We have used a new procedure that provide a quantitative determination of reactive lysine in films made from cotton-seed flour. Subsequently, this methodology was used to investigate the cross-linking of cotton-seed proteins by formaldehyde, glutaraldehyde or glyoxal in films and to analyse the relation between protein cross-linking and film maximum puncture force