Beta-lactoglobulin-dextran Maillard conjugates: their effect on interfacial thickness and emulsion stability

The influence of dextran molecular weight on the steric layer thickness and oil-in-water (O/W) emulsion flocculation stability of beta-lactoglobulin-dextran Maillard conjugates was investigated. Maillard conjugates were formed by reacting beta-lactoglobulin with various molecular weight dextrans (Mw = 18.5-440 kDa) under mild conditions (60 degrees C, 76% RH). Purified Maillard conjugates or beta-lactoglobulin were adsorbed onto latex spheres and the thickness of the adsorbed layer measured using photon correlation spectroscopy. The adsorbed layer thickness was 3 nm for beta-lactoglobulin alone. Attachment of dextran increased adsorbed layer thickness to 5 nm for the conjugate with low molecular weight dextran (Mw = 18.5 kDa) and 20 nm for that with high molecular weight dextran (Mw = 440 kDa). Enzymatic digestion of the adsorbed layers with dextranase reduced the layer to a thickness corresponding to that of beta-lactoglobulin alone. This suggests that the protein segment of the Maillard conjugate anchors the emulsifier to the interface. Attachment of dextran, irrespective of its molecular weight (18.5-440 kDa), increased the stability of emulsions against calcium induced flocculation, demonstrating that a low molecular weight dextran is sufficient for imparting high steric stability. The observation that the steric layer size was controlled by the dextran molecular weight, suggests that the results of layer thickness and emulsion stability should be universal across all globular proteins.