Effect of conjugation with glucosamine on the functional properties of lysozyme and casein

BACKGROUND: Modification with carbohydrates usually changes the functional properties of proteins. Such modification might make non‐conventional food proteins (such as plant and microbial proteins) more applicable for human consumption. The purpose of this research was to conjugate glucosamine to lysozyme and casein using a water‐soluble carbodiimide and to investigate the effect of conjugation on the functional properties of these proteins. RESULTS: Glycosylation with glucosamine converted casein to high‐molecular‐weight species which appeared as diffuse bands in sodium dodecyl sulfate polyacrylamide gel electrophoresis. Approximately 2 and 0.11 mol of glucosamine was attached to 1 mol of casein and lysozyme respectively. Both conjugated proteins exhibited improved solubility at different pHs (3 and 6) and different temperatures (25, 45 and 60 °C), increased heat stability and better emulsifying activity, emulsion stability and foaming capacity compared with the unmodified proteins (P < 0.05). CONCLUSION: These changes might increase the applicability of lysozyme as a natural antimicrobial and casein as a protein ingredient in different food systems.