The effect of glycosylation on the interfacial properties of bovine caseinomacropeptide

The two major fractions of bovine caseinomacropeptide (CMP), the glycosylated gCMP and non-glycosylated aCMP, were studied for their emulsifying properties. The main finding was that aCMP showed significantly better emulsifying properties than gCMR. While aCMP showed an emulsifying activity index ;EAI) of 150.7 g/m(2), gCMP achieved a value of 98.5 g/m(2). Stability of emulsions was 1.4 times higher for aCMP as compared to gCMP. Droplet size measurements and creaming studies showed a strong influence of pH on both fractions with minimal emulsion stabilities at pH 4.1 (gCMP) and 4.9 (aCMP). Investigation of the flocculation behaviour and variations of the ionic strength indicate that the glycan side chains induce a combination of electric, steric and hydrophilic effects, preventing an ordered adsorption of gCMP molecules at the oil/water interface, while aCMP builds a stable network at the surface. For further elucidation, zeta potential measurements for both fractions were performed, resulting in isoelectric points of 3.15 for gCMP and 4.15 for aCMP in bulk solution. Finally, a hypothesis of surface adsorption of CMP is presented as a function of glycosylation and pH based on experimental data supported by an approach using protein modelling techniques. (C) 2009 Elsevier Ltd. All rights reserved.