CREAMING AND FLOCCULATION OF OIL-IN-WATER EMULSIONS CONTAINING SODIUMCASEINATE

The influence of protein content on the stability of concentrated oil- in-water emulsions (35 or 45 vol% oil, droplet diameter similar to 0.5 mu m, pH 6.8) containing sodium caseinate as the sole emulsifying age nt has been investigated. Time-dependent creaming profiles were determ ined at 30 degrees C using an ultrasound velocity scanning technique w ith data analysis based on a Urick equation renormalization technique. The results indicate that creaming kinetics has a complex dependence on caseinate content. At low protein content (1 wt%), corresponding to less than half that required for saturation monolayer coverage, the e mulsion is destabilized by bridging flocculation (accompanied by some coalescence). At higher protein content (2 wt%), where individual drop lets are fully protected against protein bridging or coalescence by th e thick adsorbed protein layer, the unflocculated emulsion has good st ability over a period of several weeks. With further increase of prote in content (greater than or equal to 3 wt%), the observed creaming sta bility is reduced again, with the rate of serum separation at the bott om of the sample now greatly increased. This is attributed here to dep letion flocculation by unadsorbed caseinate, probably in the form of s mall particles called ''casein submicelles.'' Light microscopy has con firmed that the visually observable extent of reversible depletion flo cculation in concentrated emulsions of this type is very sensitive to overall protein content. Once the caseinate concentration reaches a hi gh value (6 wt%), the strength of the depletion interaction is such th at it produces a very strong emulsion droplet network which can reorga nize only slowly, and is hence much more stable to creaming and serum separation. (C) 1997 Academic Press