Formation and characterization of amphiphilic conjugates of whey protein isolate (WPI)/xanthan to improve surface activity

Proteins, polysaccharides and their blends, as examples of natural biopolymers, may be considered as amphiphilic macromolecules that play an essential role in stabilizing food formulations (foams, emulsions and dispersions). Under specific compositions and conditions (protein-to-polysaccharide ratio, pH, ionic strength, temperature, mixing, processing steps) proteins and polysaccharides form water-soluble hybrids (complexes or conjugates), but not coacervates, with enhanced functional properties in comparison to the proteins and polysaccharides alone. Aqueous mixtures of WPI (4-10wt%) and xanthan gum (> 0.5wt%) form clear aqueous systems exhibiting new physicochemical properties such as rheological behavior, surface properties, surface density of charge (zeta potential), surface hydrophobicity and diffusion behavior. Electrostatic interactions and thermodynamic incompatibility in mixed biopolymer solutions were correlated to the functional properties (rheology, surface properties and surface hydrophobicity) of these adducts. Evidences for associative interactions between WPI and xanthan gum have been established by studying the rheological behavior, the surface hydrophobicity and the surface dynamic properties of the blends. The electrostatic and hydrophobic interactions form hybrids that can provide a synergistic effect on the emulsifying capabilities of the biopolymers and can increase the stability of emulsion droplets against coalescence and flocculation. (c) 2006 Elsevier Ltd. All rights reserved.