Effect of Maillard-based conjugation with dextran on the functional properties of lysozyme and casein

The purpose of this research was to find the best experimental conditions for glycosylation of lysozyme and casein with dextran, and to investigate the effect of glycosylation on the functional properties of these proteins. Glycosylation was performed by allowing proteins to react with dextran under Maillard reaction conditions. The extent of glycosylation was determined by sugar analysis, SDS-PAGE, gel filtration and cation-exchange chromatography. Glycosylation of lysozyme with a 1:5 weight ratio of protein to dextran, held at 60 degrees C for one week under a relative humidity of 79% resulted in coupling of 3.0 mole dextran to one mole lysozyme. In the case of casein, at 60 degrees C, 48 h and 79% relative humidity, 0.1 and 0.13 mole dextran was attached to one mole of casein when a weight ratio of protein to dextran of 1:5 and 1:7.5 was used, respectively. A decrease in the degree of glycosylation occurred when samples were incubated for 72 h. Enzymatic activity of glycosylated lysozyme was reduced by 20% compared with unmodified lysozyme (P < 0.05). Both proteins exhibited improved solubility at different pH values (3, 7 and 9), different temperatures (25, 40 and 60 degrees C) and increased heat stability, with a better emulsion activity and emulsion stability than with un-modified proteins (P < 0.05). These changes might increase the applicability of lysozyme as a natural antimicrobial and casein as a protein ingredient in different food systems. (c) 2005 Society of Chemical Industry.