Fernández-Ventoso Lucía, Toba-Pérez Artai, Losada-Barreiro Sonia, Paiva-Martins Fátima, Bravo-Díaz Carlos
Departamento Química-Física, Facultad de Química, Universidade de Vigo, 36310 Vigo, Spain.
REQUIMTE-LAQV, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, 4169-007 Porto, Portugal.
Antioxidants (Basel). 2022 Dec 16;11(12):2477. doi: 10.3390/antiox11122477.
During the last years, the formalism of the pseudophase kinetic model (PKM) has been successfully applied to determine the distributions of antioxidants and their effective interfacial concentrations, and to assess the relative importance of emulsion and antioxidant properties (oil and surfactant nature, temperature, acidity, chemical structure, hydrophilic-liphophilic balance (HLB), etc.) on their efficiency in intact lipid-based emulsions. The PKM permits separating the contributions of the medium and of the concentration to the overall rate of the reaction. In this paper, we report the results of a specifically designed experiment to further test the suitability of the PKM to evaluate the distributions of antioxidants among the various regions of intact lipid-based emulsions and provide insights into their chemical reactivity in multiphasic systems. For this purpose, we employed the antioxidants α- and δ-TOCopherol (α- and δ-TOC, respectively) and determined, at different acidities well below their pa, the interfacial rate constants for the reaction between 16-ArN and α- and δ-TOC, and the antioxidant distributions in intact emulsions prepared with olive and soybean oils. Results show that the effective interfacial concentration of δ-TOC is higher than that of α-TOC in 1:9 (/) soybean and 1:9 olive oil emulsions. The effective interfacial concentrations of tocopherols are much higher (15-96-fold) than the stoichiometric concentrations, as the effective interfacial concentrations of both δ-TOC and α-TOC in soybean oil emulsions are higher (2-fold) than those in olive oil emulsions. Overall, the results demonstrate that the PKM grants an effective separation of the medium and concentration effects, demonstrating that the PKM constitutes a powerful non-destructive tool to determine antioxidant concentrations in intact emulsions and to assess the effects of various factors affecting them.
在过去几年中，伪相动力学模型（PKM）的形式体系已成功应用于确定抗氧化剂的分布及其有效界面浓度，并评估乳液和抗氧化剂性质（油和表面活性剂性质、温度、酸度、化学结构、亲水亲油平衡（HLB）等）对其在完整脂质基乳液中效率的相对重要性。PKM能够分离介质和浓度对总反应速率的贡献。在本文中，我们报告了一项专门设计的实验结果，以进一步测试PKM评估完整脂质基乳液各区域中抗氧化剂分布的适用性，并深入了解其在多相体系中的化学反应性。为此，我们使用了抗氧化剂α-生育酚和δ-生育酚（分别为α-TOC和δ-TOC），并在远低于其pKa的不同酸度下，测定了16-ArN与α-TOC和δ-TOC之间反应的界面速率常数，以及用橄榄油和大豆油制备的完整乳液中的抗氧化剂分布。结果表明，在1:9（体积比）的大豆和橄榄油乳液中，δ-TOC的有效界面浓度高于α-TOC。生育酚的有效界面浓度比化学计量浓度高得多（15-96倍），因为大豆油乳液中δ-TOC和α-TOC的有效界面浓度都高于橄榄油乳液（2倍）。总体而言，结果表明PKM能够有效分离介质和浓度效应，证明PKM是一种强大的非破坏性工具，可用于确定完整乳液中的抗氧化剂浓度，并评估影响它们的各种因素的作用。
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