Whey-protein / polysaccharide coacervates : structure and dynamics

This thesis studied the interactions between food ingredients under acidic conditions (like in yoghurt or in soft drinks for instance). In the chapters 2, 3, and 4, the author investigated the conditions under which a complex was formed between positively charged whey proteins (proteins derived from milk) and a negatively charged polysaccharide. Three different polysaccharides, which are commonly added into food products as thickeners, were used: gum arabic, the exopolysaccharide EPS B40 and carrageenan. The properties of whey protein / polysaccharide electrostatic complexes could be tuned by varying key parameters such as pH, ionic strength and concentrations. The last chapters focused on the system whey protein / gum arabic. A concentrated phase was made of whey proteins and gum arabic, also called coacervate phase. This phase had very interesting features; it was very viscous but always remained liquid. The properties of the coacervate phase were studied in chapters 5, 6, and 7 and they could be explained by the strength of electrostatic interactions. At the pH where the interactions were the strongest, the coacervate phase was the most concentrated in polymer, the most viscous, the densest and the most structured. At this pH the diffusion of the polymer was also slower. The coacervate phase was made of protein and polysaccharide that moved independently within the coacervate phase. In time the coacervate phase rearranged, became transparent, and the diffusion of the polymer was slower. Finally, in chapter 8, a direct application of the whey protein / gum arabic coacervate was used as a coating around sensitive materials (like flavors or drugs) and, as an example, flavors were added to cheese.