Ghosh S, Rousseau D
Department of Chemistry and Biology, Ryerson University, Toronto, Ont., Canada M5B 2K3.
J Colloid Interface Sci. 2009 Nov 1;339(1):91-102. doi: 10.1016/j.jcis.2009.07.047. Epub 2009 Jul 25.
Factors influencing water-in-oil emulsion stability during freeze/thaw-cycling, namely interfacial crystallization vs. network crystallization and the sequence of crystallization events (i.e., dispersed vs. continuous phase or vice versa), are assessed. We show that destabilization is most apparent with a liquid-state emulsifier and a continuous oil phase that solidifies prior to the dispersed phase. Emulsions stable to F/T-cycling are obtained when the emulsifier crystallizes at the oil-water interface or in emulsions where the continuous phase crystallizes after the dispersed aqueous phase. The materials used are two food-grade oil-soluble emulsifiers - polyglycerol polyricinoleate (PGPR) and glycerol monostearin (GMS) and two continuous oil phases with differing crystallization temperatures - canola oil and coconut oil. Emulsion stability is assessed with pulsed field gradient NMR droplet size analysis, sedimentation, microscopy and differential scanning calorimetry. This study demonstrates the sequence of crystallization events and the physical state of the surfactant at the oil-water interface strongly impact the freeze-thaw stability of water-in-oil emulsions.
评估了在冻融循环过程中影响油包水乳液稳定性的因素，即界面结晶与网络结晶以及结晶事件的顺序（即分散相还是连续相先结晶，反之亦然）。我们发现，对于液态乳化剂和连续油相在分散相之前固化的情况，乳液失稳最为明显。当乳化剂在油水界面结晶时，或者在连续相在分散水相之后结晶的乳液中，可以获得对冻融循环稳定的乳液。所使用的材料是两种食品级油溶性乳化剂——聚甘油聚蓖麻醇酸酯（PGPR）和甘油单硬脂酸酯（GMS），以及两种具有不同结晶温度的连续油相——菜籽油和椰子油。通过脉冲场梯度核磁共振液滴尺寸分析、沉降、显微镜观察和差示扫描量热法评估乳液稳定性。本研究表明，结晶事件的顺序以及油水界面处表面活性剂的物理状态对油包水乳液的冻融稳定性有强烈影响。
