HPLC DETERMINATION OF THE REACTIVE LYSINE CONTENT OF COTTONSEED PROTEIN FILMS TO MONITOR THE EXTENT OF CROSS-LINKING BY FORMALDEHYDE, GLUTARALDEHYDE, AND GLYOXAL

A sensitive and reproductible HPLC method to determine the reactive ly sine content of films made from cottonseed flour was developed. This m ethod is applied to follow the cross-linking of cottonseed proteins by formaldehyde, glutaraldehyde, or glyoxal. The cross-linking of these proteins resulted in the decrease of reactive lysine content within th e film. The maximum puncture force of the films is correlated with the modified reactive lysine content after cross-linking treatments. Of t he three cross-linking agents, formaldehyde was the most effective to enhance the maximum puncture force of the films despite its moderate r eaction with only 50% of reactive lysine in the films. By contrast, gl utaraldehyde, which reacted with nearly 100% of lysine, led to less re sistant films. The results were interpreted as the impact of the molec ular structure of the cross-link bridges on the mobility between prote in chains.