Dickinson E, Golding M, Povey MJW
Procter Department of Food Science, University of Leeds, Leeds, LS2 9JT, United Kingdom
J Colloid Interface Sci. 1997 Jan 15;185(2):515-29. doi: 10.1006/jcis.1996.4605.
The influence of protein content on the stability of concentrated oil-in-water emulsions (35 or 45 vol% oil, droplet diameter approximately 0.5 &mgr;m, pH 6.8) containing sodium caseinate as the sole emulsifying agent has been investigated. Time-dependent creaming profiles were determined at 30°C using an ultrasound velocity scanning technique with 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 emulsion is destabilized by bridging flocculation (accompanied by some coalescence). At higher protein content (2 wt%), where individual droplets are fully protected against protein bridging or coalescence by the thick adsorbed protein layer, the unflocculated emulsion has good stability over a period of several weeks. With further increase of protein content (>/=3 wt%), the observed creaming stability is reduced again, with the rate of serum separation at the bottom of the sample now greatly increased. This is attributed here to depletion flocculation by unadsorbed caseinate, probably in the form of small particles called "casein submicelles." Light microscopy has confirmed that the visually observable extent of reversible depletion flocculation in concentrated emulsions of this type is very sensitive to overall protein content. Once the caseinate concentration reaches a high value (6 wt%), the strength of the depletion interaction is such that it produces a very strong emulsion droplet network which can reorganize only slowly, and is hence much more stable to creaming and serum separation.
研究了蛋白质含量对以酪蛋白酸钠作为唯一乳化剂的浓缩水包油乳液（油含量为35或45体积%，液滴直径约0.5μm，pH值6.8）稳定性的影响。在30℃下，使用超声速度扫描技术并基于Urick方程重归一化技术进行数据分析，测定了随时间变化的乳析曲线。结果表明，乳析动力学对酪蛋白酸盐含量具有复杂的依赖性。在低蛋白质含量（1 wt%）时，对应于饱和单层覆盖所需量的不到一半，乳液因桥连絮凝（伴有一些聚结）而不稳定。在较高蛋白质含量（2 wt%）时，单个液滴被厚厚的吸附蛋白质层完全保护，免受蛋白质桥连或聚结，未絮凝的乳液在几周内具有良好的稳定性。随着蛋白质含量进一步增加（≥3 wt%），观察到的乳析稳定性再次降低，此时样品底部血清分离的速率大大增加。这在此归因于未吸附的酪蛋白酸盐的耗尽絮凝，可能是以称为“酪蛋白亚胶粒”的小颗粒形式存在。光学显微镜已证实，在这种类型的浓缩乳液中，视觉上可观察到的可逆耗尽絮凝程度对总蛋白质含量非常敏感。一旦酪蛋白酸盐浓度达到高值（6 wt%），耗尽相互作用的强度会产生一个非常强的乳液液滴网络，该网络只能缓慢重组，因此对乳析和血清分离更稳定。
