Interactions between milk whey protein and polysaccharide in solution

In this work we have studied the interactions between a commercial whey protein concentrate (WPC) and two anionic polysaccharides (sodium alginate, SA, and λ-carrageenan, λ-C) in the aqueous phase. The concentration of WPC at 1.0% and the pH 7.0 of the aqueous phase were maintained constant, while polysaccharides (PS) were evaluated within a 0.0–1.0% concentration range. Interactions between WPC and PS in the aqueous phase were analysed by fluorescence spectroscopy, absorption spectroscopy in the presence of methylene blue (MB), and confocal laser scanning microscopy. The results from these methodologies revealed differences in the molecular dynamics of mixed systems. The nature of the interactions between WPC and PS depended on the PS type, its relative concentration in the aqueous phase and also on the two WPC fractions. Whey protein concentrate/sodium alginate (WPC/SA) mixed systems were distinguished by a tendency to protein aggregation in the aqueous phase and their segregation into separated microdomains. On the other hand, WPC/λ-carrageenan (WPC/λ-C) mixed systems showed a high degree of attractive interactions over the whole range of concentrations. The ultrastructure revealed the existence of hybrid macromolecular entities (biopolymer network). Interaction of WPC and polysaccharide in the aqueous phase has an effect on the adsorption of mixed systems at the air–water interface and on their foaming characteristics.