Kim H-J, Decker E A, McClements D J
Biopolymers and Colloids Research Laboratory, Department of Food Science, University of Massachusetts, Amherst, Massachusetts 01003, USA.
J Agric Food Chem. 2002 Nov 20;50(24):7131-7. doi: 10.1021/jf020366q.
The influence of globular protein denaturation after adsorption to the surface of hydrocarbon droplets on flocculation in oil-in-water emulsions was examined. n-Hexadecane oil-in-water emulsions (pH 7.0) stabilized by beta-lactoglobulin (1-wt % beta-Lg) were prepared by high-pressure valve homogenization. NaCl (0-150 mM) was added to these emulsions immediately after homogenization, and the evolution of the mean particle diameter (d) and particle size distribution (PSD) was measured by laser diffraction during storage at 30 degrees C for 48 h. No change in d or PSD was observed in the absence of added salt, which indicated that these emulsions were stable to flocculation. When 150 mM NaCl was added to emulsions immediately after homogenization, d increased rapidly during the following few hours until it reached a plateau value, while the PSD changed from monomodal to bimodal. Addition of N-ethylmaleimide, a sulfhydryl blocking agent, to the emulsions immediately after homogenization prevented (at 20 mM NaCl) or appreciably retarded (at 150 mM NaCl) droplet flocculation. These data suggests that protein unfolding occurred at the droplet interface, which increased the hydrophobic attraction and disulfide bond formation between droplets. In the absence of added salt, the electrostatic repulsion between droplets was sufficient to prevent flocculation, but in the presence of sufficient salt, the attractive interactions dominated, and flocculation occurred.
研究了球状蛋白质吸附到烃类液滴表面后变性对水包油乳液中絮凝作用的影响。通过高压阀匀浆法制备了由β-乳球蛋白（1 wt%β-Lg）稳定的正十六烷水包油乳液（pH 7.0）。匀浆后立即向这些乳液中加入NaCl（0 - 150 mM），并在30℃下储存48小时期间通过激光衍射测量平均粒径（d）和粒径分布（PSD）的变化。在未添加盐的情况下，未观察到d或PSD的变化，这表明这些乳液对絮凝作用是稳定的。当在匀浆后立即向乳液中加入150 mM NaCl时，d在接下来的几个小时内迅速增加，直至达到平稳值，而PSD从单峰变为双峰。在匀浆后立即向乳液中加入巯基封闭剂N-乙基马来酰亚胺，可防止（在20 mM NaCl时）或显著延迟（在150 mM NaCl时）液滴絮凝。这些数据表明蛋白质在液滴界面发生了去折叠，这增加了液滴之间的疏水吸引力和二硫键形成。在未添加盐的情况下，液滴之间的静电排斥足以防止絮凝，但在存在足够盐的情况下，吸引相互作用占主导，絮凝发生。
