Stability of Emulsions Containing Both Sodium Caseinate and Tween 20

The creaming and rheology of oil-in-water emulsions (30 vol% n-tetradecane, pH 6.8) stabilized by a mixture of commercial sodium caseinate and the non-ionic emulsifier polyoxyethylene sorbitan monolaurate (Tween 20) has been investigated at 21 degrees C. The presence of sufficient Tween 20 to displace most of the protein from the emulsion droplet surface leads to greatly enhanced emulsion creaming (and strongly non-Newtonian rheology) which is indicative of depletion flocculation by nonadsorbed surface-active material (protein and emulsifier). In emulsions containing a constant amount of surface-active material, the replacement of a very small fraction of Tween 20 by caseinate in a stable pure Tween 20 emulsion leads to enhanced creaming for a small fraction of the droplets, and this fraction increases with increasing replacement of emulsifier by protein. This behavior is probably due to depletion flocculation, although an alternative bridging mechanism is also a possibility. The overall stability of these sets of emulsions can be represented in terms of a global stability diagram containing regions of bridging flocculation and coalescence (low content of surface-active material), stability (intermediate content), and depletion flocculation (high content). Copyright 1999 Academic Press.