Casein micelles and their interaction with exo-polysaccharides; Turbidity and viscosity

We made a systematic investigation of the interaction of an exo-polysaccharide (EPS) with casein micelles as present in skim milk. The EPS was produced by the lactic acid bacterium Lactococcus lactis subsp. cremoris strain NIZO B40. The interaction of the EPS with milk components is of relevance for the consistency of fermented milk products. Low-heat skim milk was used to model a casein micelle suspension. At low EPS concentrations the mixture was stable. At higher concentrations the mixtures exhibited phase separation due to depletion interactions. In the one-phase region the strength of the segregative interaction could be determined from turbidity and rheological measurements. Then, by applying statistical mechanical methods the position of the phase boundary could be estimated. The viscosity of the mixtures was increased due to the segregative interactions in the EPS/casein micelle mixtures. The segregative interactions are of relevance for the final rheological properties of food products.