Wageningen University, Department of Agrotechnology & Food Sciences, Laboratory of Food Process Engineering Group, Bornse Weilanden 9, 6708 WG Wageningen, the Netherlands; Membrane Processes for Food Group, University of Twente, Drienerlolaan 5, 7522 NB Enschede, the Netherlands.
Wageningen University, Department of Agrotechnology & Food Sciences, Laboratory of Food Process Engineering Group, Bornse Weilanden 9, 6708 WG Wageningen, the Netherlands; INRAE, UR BIA, F-44316 Nantes, France.
Food Res Int. 2022 Oct;160:111621. doi: 10.1016/j.foodres.2022.111621. Epub 2022 Jul 15.
Lipid oxidation is a longstanding topic within the field of food technology, and is strongly related to loss of product quality and consumer acceptance. Both for bulk oils and emulsions, the chemical phenomena involved in lipid oxidation have been extensively researched, and various reaction pathways have been identified. They are different in bulk oil compared to oil-in-water (O/W) emulsions in which the oil-water interface plays a prominent role. Most probably because of the complexity of the reaction scheme in combination with mass transfer effects, there is no model that describes lipid oxidation in emulsions in a unified fashion, and that is the aim that we have set ourselves to achieve. We use lipid oxidation data previously obtained in O/W emulsions made with 5 different emulsifiers (2 surfactants, and 3 proteins), in well-mixed systems where the oxygen-to-oxidizable lipid ratio is strictly controlled. We use data pertaining to headspace oxygen concentration, and to primary and secondary lipid oxidation products to develop a model based on reaction kinetics, including not only the classical reaction scheme (starting from an unsaturated lipid, LH) but also radical initiation from hydroperoxides, which is thought to be an effect that is overlooked in the classical description of the initiation step. We were able to describe the course of the reactions in these emulsions using the same reaction rate constants for all emulsions, with the exception of the two related to radical-based initiation. In Tween 20- and Tween 80-stabilized emulsions, initiation stems most probably solely from decomposition of hydroperoxides; this implies that lipid oxidation in these emulsions is co-determined by the initial ("pre-existing") hydroperoxide concentration. In protein-stabilized emulsions, on the other hand, lipid radical initiation is probably linked to reactions involving proteins (co-oxidation reactions), whereas initiation through decomposition of hydroperoxides seems less important, if at all. From this, we can conclude that the difference between both types of emulsions with regard to lipid oxidation mechanisms is related to differences in radical initiation. The developed model can serve as a unified basis for understanding lipid oxidation in emulsions, through which additional effects beyond the bare reaction kinetics, such as mass transfer effects, can be identified and used to e.g., quantify antioxidant effects, which is part of follow-up research.
脂质氧化是食品技术领域中长期存在的一个课题，与产品质量损失和消费者接受度密切相关。无论是对于散装油还是乳液，涉及脂质氧化的化学现象都已经得到了广泛的研究，并且已经确定了各种反应途径。它们在散装油中与油包水 (O/W) 乳液不同，因为油-水界面在其中起着突出的作用。很可能是由于反应方案的复杂性以及传质效应的影响，目前还没有一个模型能够以统一的方式描述乳液中的脂质氧化，这也是我们设定的目标。我们使用之前在使用 5 种不同乳化剂（2 种表面活性剂和 3 种蛋白质）制备的 O/W 乳液中获得的脂质氧化数据，这些乳液在充分混合的系统中，氧与可氧化脂质的比例受到严格控制。我们使用与顶空氧浓度以及初级和次级脂质氧化产物有关的数据，基于反应动力学开发了一个模型，该模型不仅包括经典的反应方案（从不饱和脂质 LH 开始），还包括来自氢过氧化物的自由基引发，这被认为是经典引发步骤描述中被忽视的一个效应。我们能够使用所有乳液的相同反应速率常数来描述这些乳液中反应的过程，除了与基于自由基的引发相关的两个反应速率常数。在 Tween 20 和 Tween 80 稳定的乳液中，引发最有可能仅来自氢过氧化物的分解；这意味着这些乳液中的脂质氧化由初始（“预先存在”）氢过氧化物浓度共同决定。另一方面，在蛋白质稳定的乳液中，脂质自由基的引发可能与涉及蛋白质的反应（共氧化反应）有关，而通过氢过氧化物的分解引发似乎不太重要，如果有的话。由此，我们可以得出结论，两种类型的乳液在脂质氧化机制方面的差异与自由基引发的差异有关。所开发的模型可以作为理解乳液中脂质氧化的统一基础，通过该模型可以识别除了纯粹的反应动力学之外的其他影响，例如传质效应，并用于例如量化抗氧化剂的效果，这是后续研究的一部分。
