Physical stability, microstructure and rheology of sodium-caseinate-stabilized emulsions as influenced by protein concentration and non-adsorbing polysaccharides.



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Food Hydrocolloids








We explored the stability and rheological properties of 30% oil-in-water emulsions stabilized with sodium caseinate (1–10% w/w). The dynamics of the formation of a transient droplet network were investigated using microstructure, rheology and creaming. The behaviour was classified into two types of depletion-flocculated caseinate emulsions: (1) emulsions with intermediate caseinate concentrations (1.5–4%) displayed rapid phase separation because of compaction of the flocculated networks; (2) emulsions with high caseinate concentrations (5–10%) displayed increased creaming stability, because the higher continuous phase concentration contributed to retarded formation of the viscous transient droplet network with stronger attractions. Small deformation rheology showed that the development of a transient droplet network depended markedly on the caseinate concentration. We distinguished between the contributions of the continuous phase viscosity and the depletion force by investigating the influence of maltodextrin and xanthan gum on the stability and rheology of 1.5% caseinate emulsions. Surprisingly, the droplet–droplet interactions were weakened by the addition of maltodextrin, and the stabilizing mechanism differed from the prediction that high zero shear viscosity is the dominant factor in preventing phase separation of a depletion-flocculated emulsion. We attributed the change in the depletion force to the change in caseinate particle size; a small change in caseinate size could have changed the depletion interaction potential moderately. Furthermore, the droplet rearrangements within the flocculated network played an important role in the stability of the emulsions, and were possibly influenced by both the strength of the depletion force and the continuous phase viscosity at high caseinate concentrations. Both depletion force and continuous phase viscosity increased with the addition of xanthan gum. The phase separation kinetics and the restabilization mechanisms were analogous to those of the caseinate system.