The effect of glycosylation on physicochemical and functional properties of soy glycinin

Abstract

Two glycoconjugates, maltosyl glycerin and dextranyl glycerin conjugates were formed by reductive alkylation and imidocarbonate method, respectively. Modifications of lysyl residues were 15, 34, and 45% for maltosyl glycerin conjugates and 13, 31 and 90% for dextranyl glycerin conjugates. The electrophoretic behavior of conjugates provided evidence that carbohydrates were covalently attached to glycerin. As modification of lysyl residues increased, the bands for maltosyl glycerin conjugates became broader and fainter with lower mobility. Dextranyl glycerin conjugates formed compounds of high molecular weight, which could not enter the gel and thereby were not separated in running gel. Maltosyl glycerin conjugates exhibited higher U.V. absorption at 280 nm than unmodified glycerin with some blue shifts. Dextranyl glycerin conjugates also had higher U.V. absorption at 280 nm than unmodified glycerin with maximum absorption at 250 nm. Surface hydrophobicity of maltosyl and dextranyl glycerin conjugates increased as modification of lysyl groups increased. In comparing two glycoproteins on the basis of the same degree of modified lysyl residues and the same amount of glucose bound to them, maltosyl glycerin conjugate exhibited significantly higher surface hydrophobicity than dextranyl glycerin conjugate. Based on the result of surface hydrophobicity, maltosyl glycerin conjugates were more unfolded than dextanyl glycerin conjugates Maltosyl and dextranyl glycerin conjugates had similar hydrolysis by trypsin and chymotrypsin at similar level of modified lysyl residues. Initial hydrolytic rate of maltosyl glycerin conjugate was significantly lower than that of glycerin, while the difference was not significant between dextranyl glycerin conjugate and glycerin. Dextratlyl glycerin conjugate exhibited significantly higher emulsifying activity and emulsion stability than unmodified glycerin and maltosyl glycine conjugate, while foaming capacity and stability of maltosyl glycerin conjugate were higher than unmodified glycerin and dextranyl glycerin conjugate. Improved functional properties of glycoproteins can be explained by not one characteristic, but by the combined effect of several factors, such as size and structure of carbohydrate, surface hydrophobicity and flexibility of protein and crossbarring of protein.