Whey protein aggregates and their interaction with exo-polysaccharides

Summary We made a systematic investigation of the interaction of an exo‐polysaccharide (EPS) with whey proteins. The EPS was produced by a lactic acid bacterium Lactococcus lactis subsp. cremoris strain NIZO B40. The interaction of the EPS with milk components is of relevance to the consistency of fermented milk products. EPS and whey protein isolates (WPI) can be mixed in all proportions. Even at an EPS concentration of 10 g.L−1 no instability is visible. In yoghurt milk the whey proteins are usually denatured. We prepared aggregated whey protein colloid particles (AWC particles) which had an average radius of 27 ± 3 nm, as derived from the radius of gyration. The interaction of AWC particles and EPS was studied at a neutral pH and an ionic strength of 0.1 m. At low EPS concentrations the mixture was stable. At higher concentrations the mixtures showed phase separation owing to depletion interactions. In the one‐phase region the strength of the segregative interaction can be determined from turbidity, light scattering and neutron scattering measurements. Then, by applying statistical mechanical methods, the position of the phase boundary could be predicted. The viscosity of the mixtures was increased owing to the segregative interactions in the EPS/AWC mixtures. Within the two‐phase region the mixtures showed so‐called spinodal decomposition, during which different microstructures were formed. Understanding the formation of such structures is of interest for the development of new food structures.