ROLE OF POSITIVE CHARGE OF LYSOZYME IN THE EXCELLENT EMULSIFYING PROPERTIES OF MAILLARD-TYPE LYSOZYME POLYSACCHARIDE CONJUGATE

Maillard-type lysozyme-polysaccharide conjugates revealed the best emulsifying properties among various protein-polysaccharide conjugates. To elucidate the mechanism of the excellent emulsifying properties of Maillard-type lysozyme-polysaccharide conjugate, the emulsifying properties of the galactomannan conjugate with alpha-lactalbumin having extensive structural homology with lysozyme were compared to those of lysozyme-galactomannan conjugate. The lysozyme and alpha-lactalbumin were attached two and three galactomannans per mole of protein, respectively, through Maillard reaction in a dry state at 60 degrees C under 79% relative humidity for 2 weeks. The emulsion stability of alpha-lactalbumin was not so remarkably improved by conjugating with galactomannan as that of lysozyme, although the emulsifying activities of both protein-galactomannan conjugates were almost the same. The emulsion stability of lysozyme-galactomannan conjugates was greatly decreased with the extent of the acetylation of lysyl residues. These results suggest that the electrostatic repulsion of positive charge in the lysozyme molecule is attributed to the excellent emulsifying properties of lysozyme-galactomannan conjugate.