Competitive adsorption of proteins with methylcellulose and hydroxypropyl methylcellulose

Surface-active polysaccharides are attracting increasing interest for use in a variety of applications. Amongst these, methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC) have been developed, in part, for their foam and emulsion stabilising properties, together with their water holding and viscosity enhancing properties. The aim of this research is to quantify the competitive adsorption between proteins and MC/HPMC, as they are often used together in many applications, and the results of potential effects of competition are unknown. Two proteins were compared; β-lactoglobulin (BLG) and β-casein (BCAS). BLG forms an elastic interface, whereas BCAS does not. Hence, BCAS is displaced by surfactants more easily than BLG. The surface rheology, surface tension and foam stability of the mixed protein:polysaccharide systems were determined to elucidate the mechanism and consequences of competition. In contrast to surfactants, both MC and HPMC formed highly elastic interfaces, more elastic even than BLG. Both HPMC and MC were more surface active than the proteins, therefore at higher MC and HPMC concentrations, the polysaccharides began to dominate the interfacial properties. Whereas surfactants reduce the elasticity of the protein adsorbed layer, the elastic properties of the polysaccharides enhanced the overall strength of the interface, which will potentially result in more stable foams.