Abstract

Whey protein isolate (WPI) is an excellent emulsifier. However, WPI-stabilized emulsions tend to flocculate at pH values close to their isoelectric point. In this work, a layer by layer (LBL) technique was used to develop double layer oil in water emulsions using a mixture of WPI and water-soluble fraction of Persian gum (WSPG). Polysaccharide concentration and pH were found to have a major impact on the stability of the final system. At a constant total biopolymer concentration, increasing the amount of WSPG significantly (p < 0.05) improved the emulsion physical stability. An appropriate stability was obtained at 0.5 wt% WPI, 1 wt% WSPG, and pH 5.0. At high ionic strength, the emulsions became unstable with a higher sensitivity to CaCl₂ than NaCl. Confocal laser scanning microscopy and zeta-potential measurements confirmed the electrostatic adsorption of WSPG onto the WPI-stabilized oil droplets. The results of interfacial tension and dilatational rheology measurements revealed a slight decrease in the interfacial tension after the adsorption of WSPG as the second layer and a predominantly elastic behavior (E′ > E″), at the interface especially at pH 5.0. The results showed that WSPG is an appropriate candidate for improving the physical stability of WPI-stabilized emulsions at pH values close to isoelectric point.

摘要

乳清分离蛋白 (WPI) 是一种极好的乳化剂。然而，WPI 稳定的乳液倾向于在接近其等电点的 pH 值下絮凝。在这项工作中，使用 WPI 和波斯胶的水溶性部分 (WSPG) 的混合物，使用逐层 (LBL) 技术开发双层水包油乳液。发现多糖浓度和 pH 值对最终系统的稳定性有重大影响。在恒定的总生物聚合物浓度下，增加 WSPG 的量显着 (p < 0.05) 改善了乳液的物理稳定性。在 0.5 wt% WPI、1 wt% WSPG 和 pH 5.0 下获得了适当的稳定性。在高离子强度下，乳液变得不稳定，对 CaCl _{2 的}敏感性更高比氯化钠。共聚焦激光扫描显微镜和 zeta 电位测量证实了 WSPG 静电吸附到 WPI 稳定的油滴上。界面张力和膨胀流变测量的结果表明，在吸附作为第二层 WSPG 后界面张力略有下降，并且在界面处尤其是在 pH 5.0 时具有主要的弹性行为（E ' > E '' ）。结果表明，WSPG 是提高 WPI 稳定乳液在接近等电点的 pH 值下物理稳定性的合适候选物。