of around 15% alcohol content can be made to have a shelf The effect of alcohol on the stability of oil-in-water emulsions life of several years. Experiments on effects of alcohol conof similar mean droplet size made with 4 wt% sodium caseinate centration on the stability of model emulsions containing and 35 vol% n-tetradecane was investigated. Controlled stress sodium caseinate as the primary emulsifier have shown (3viscometry showed that, shortly after preparation, emulsions con-5) that, above a certain critical concentration of alcohol taining 25 vol% ethanol are of low viscosity and almost Newtonian (30-40 wt%, depending on protein concentration), the sysin character. In contrast, emulsions containing little or no alcohol tems are unstable with respect to creaming. Protein precipita-(ยฐ10 vol%) exhibit psuedoplastic behavior with a much higher tion and droplet aggregation takes place because the ethanollimiting low-stress viscosity. Time-dependent creaming profiles rich aqueous phase is a poor solvent for the protein (6). At were determined at 30ะC using an ultrasound velocity scanning technique with a linear renormalization data analysis. The addi-alcohol concentrations close to the protein solubility limit, tion of alcohol was found to have relatively little effect on the the lowering of solvent quality causes a flattening of the long-term creaming stability, which was uniformly characteristic ''hairy layer,'' thus reducing steric stabilization (7). The of a flocculated emulsion. The presence of alcohol leads to Ostwald addition of alcohol also causes a reduction of the dielectric ripening, as demonstrated by the gradual shift in monomodal constant with a consequent negative influence on the contridroplet-size distribution during prolonged storage. Ostwald ripenbution of any electrostatic stabilization mechanism.
ing is probably the main reason for the stepwise reduction in oil
At alcohol concentrations well below that causing protein concentration in the serum phase of the stored alcohol-containing precipitation, the presence of ethanol can actually enhance emulsions. Time-dependent rheology measurements of alcoholemulsion stability. This is because ethanol causes a signifirich emulsions showed an apparent shear viscosity increasing cant reduction in the interfacial tension between the oil phase steadily over a matter of hours, suggesting that flocculation was and aqueous protein solution (8), and so the homogenization not eliminated, but merely slowed, by the presence of the alcohol.
It is proposed that the presence of alcohol modifies the average of an emulsion premix containing alcohol produces oil dropsize and composition of the unadsorbed caseinate submicelles lets with a significantly lower average size than for the equivwhich are putatively responsible for the depletion flocculation. alent alcohol-free system (4). According to Stokes's law, Reducing the mean diameter of droplets in alcohol-containing the effect of reducing the average droplet size from ca. 1 emulsions by prolonged homogenization was found to enhance the mm in an emulsion without alcohol to รต0.6 mm in an emulshort-term emulsion creaming stability, but the long-term stability sion with 10-20% alcohol is to reduce the creaming speed was essentially unaffected due to the predominant influence of from ca. 11 mm day 01 to less than 4 mm day 01 (3).
Ostwald ripening.