Universidad de Vigo, Fac. Química, Dpto Química Física, 36200 Vigo, Spain.
J Colloid Interface Sci. 2012 Mar 15;370(1):73-9. doi: 10.1016/j.jcis.2011.12.057. Epub 2012 Jan 2.
We determined the effects of emulsifier concentration and temperature on the distribution of gallic acid (GA) in a food-grade emulsion composed of 1:9 vol:vol stripped corn oil, acidic water and Tween 20. The distribution of GA can be defined by the partition constant between the aqueous and the interfacial regions, P(W)(I), which was determined by using a kinetic method and the pseudophase kinetic model. Once P(W)(I) is known, determining the distribution of GA is straightforward. Our results show that at least 40% of the total GA is located in the interfacial region of the emulsion at 0.005 volume fraction of Tween 20, and this percentage increases to ca. 85% of the total GA at 0.04 volume fraction of Tween 20. The variation of P(W)(I) with the temperature was used to estimate the thermodynamic parameters for the GA transfer from the aqueous to the interfacial region of the emulsion and the activation parameters for the reaction between 16-ArN(2)(+) and GA in the interfacial region. The free energy of transfer from the aqueous to the interfacial region, ΔG(T)(0,W→I), is negative, the enthalpy of transfer is small and negative, but the entropy of transfer is large and positive. Our results demonstrate that the partitioning of GA in acidic emulsions between aqueous and interfacial regions depends primarily on droplet concentration and is only slightly dependent on temperature.
我们确定了乳化剂浓度和温度对由 1:9 体积比的脱脂玉米油、酸性水和吐温 20 组成的食品级乳液中没食子酸（GA）分布的影响。GA 的分布可以通过分配常数 P(W)(I)来定义，该常数是通过动力学方法和拟相动力学模型来确定的。一旦知道了 P(W)(I)，就可以很容易地确定 GA 的分布。我们的结果表明，在 0.005 体积分数的吐温 20 时，至少有 40%的总 GA 位于乳液的界面区，而在 0.04 体积分数的吐温 20 时，这一比例增加到约 85%的总 GA。P(W)(I)随温度的变化用于估计 GA 从水相向乳液界面区的传递热力学参数，以及界面区 16-ArN(2)(+)和 GA 之间反应的活化参数。从水相向界面区的传递自由能，ΔG(T)(0,W→I)，为负，传递焓小且为负，但传递熵大且为正。我们的结果表明，GA 在酸性乳液中从水相向界面区的分配主要取决于液滴浓度，而对温度的依赖性很小。
