INFLUENCE OF ALCOHOL ON STABILITY OF OIL-IN-WATER EMULSIONS CONTAINING SODIUM CASEINATE

The effect of alcohol on the stability of oil-in-water emulsions of si milar mean droplet size made with 4 wt% sodium caseinate and 35 vol% n -tetradecane was investigated. Controlled stress viscometry showed tha t, shortly after preparation, emulsions containing 25 vol% ethanol are of low viscosity and almost Newtonian in character. In contrast, emul sions containing little or no alcohol (less than or equal to 10 vol%) exhibit pseudoplastic behavior with a much higher limiting low-stress viscosity. Time-dependent creaming profiles were determined at 30 degr ees C using an ultrasound velocity scanning technique with a linear re normalization data analysis. The addition of alcohol was found to have relatively little effect on the long-term creaming stability, which w as uniformly characteristic of a flocculated emulsion. The presence of alcohol leads to Ostwald ripening, as demonstrated by the gradual shi ft in monomodal droplet-size distribution during prolonged storage. Os twald ripening is probably the main reason for the stepwise reduction in oil concentration in the serum phase of the stored alcohol-containi ng emulsions. Time-dependent rheology measurements of alcohol-rich emu lsions showed an apparent shear viscosity increasing steadily over a m atter of hours, suggesting that flocculation was not eliminated, but m erely slowed, by the presence of the alcohol. It is proposed that the presence of alcohol modifies the average size and composition of the u nadsorbed caseinate submicelles which are putatively responsible for t he depletion flocculation. Reducing the mean diameter of droplets in a lcohol-containing emulsions by prolonged homogenization was found to e nhance the short-term emulsion creaming stability, but the long-term s tability was essentially unaffected due to the predominant influence o f Ostwald ripening. (C) 1998 Academic Press.