Dickinson E, Golding M
Procter Department of Food Science, University of Leeds, Leeds, LS2 9JT, United Kingdom
J Colloid Interface Sci. 1998 Jan 1;197(1):133-41. doi: 10.1006/jcis.1997.5221.
The effect of alcohol on the stability of oil-in-water emulsions of similar mean droplet size made with 4 wt% sodium caseinate and 35 vol% n-tetradecane was investigated. Controlled stress viscometry showed that, shortly after preparation, emulsions containing 25 vol% ethanol are of low viscosity and almost Newtonian in character. In contrast, emulsions containing little or no alcohol (</=10 vol%) exhibit psuedoplastic behavior with a much higher limiting low-stress viscosity. Time-dependent creaming profiles were determined at 30°C using an ultrasound velocity scanning technique with a linear renormalization data analysis. The addition of alcohol was found to have relatively little effect on the long-term creaming stability, which was uniformly characteristic of a flocculated emulsion. The presence of alcohol leads to Ostwald ripening, as demonstrated by the gradual shift in monomodal droplet-size distribution during prolonged storage. Ostwald ripening is probably the main reason for the stepwise reduction in oil concentration in the serum phase of the stored alcohol-containing emulsions. Time-dependent rheology measurements of alcohol-rich emulsions showed an apparent shear viscosity increasing steadily over a matter of hours, suggesting that flocculation was not eliminated, but merely slowed, by the presence of the alcohol. It is proposed that the presence of alcohol modifies the average size and composition of the unadsorbed caseinate submicelles which are putatively responsible for the depletion flocculation. Reducing the mean diameter of droplets in alcohol-containing emulsions by prolonged homogenization was found to enhance the short-term emulsion creaming stability, but the long-term stability was essentially unaffected due to the predominant influence of Ostwald ripening. Copyright 1998 Academic Press. Copyright 1998Academic Press
研究了酒精对由4 wt%酪蛋白酸钠和35 vol%正十四烷制成的平均液滴尺寸相似的水包油乳液稳定性的影响。控制应力粘度测定表明，制备后不久，含有25 vol%乙醇的乳液粘度低，几乎呈牛顿流体特性。相比之下，含少量或不含酒精（≤10 vol%）的乳液表现出假塑性行为，极限低应力粘度高得多。使用线性重归一化数据分析的超声速度扫描技术在30℃下测定了随时间变化的乳析曲线。发现添加酒精对长期乳析稳定性影响相对较小，这是絮凝乳液的一致特征。酒精的存在导致奥斯特瓦尔德熟化，这在长时间储存期间单峰液滴尺寸分布的逐渐变化中得到了证明。奥斯特瓦尔德熟化可能是储存的含酒精乳液血清相中油浓度逐步降低的主要原因。对富含酒精乳液的随时间变化的流变学测量表明，表观剪切粘度在数小时内稳步增加，这表明酒精的存在并没有消除絮凝，只是减缓了絮凝。有人提出，酒精的存在改变了未吸附酪蛋白酸亚胶粒的平均尺寸和组成，这些亚胶粒被认为是造成耗尽絮凝的原因。发现通过长时间均质化降低含酒精乳液中液滴的平均直径可提高乳液短期乳析稳定性，但由于奥斯特瓦尔德熟化的主要影响，长期稳定性基本不受影响。版权所有1998年学术出版社。版权所有1998年学术出版社
