Epoxy fatty acids in triacylglycerols: Elucidating the influences of oxidation conditions and lipid structures on formation and accumulation during lipid oxidation to enable their precise analysis in food

食物中的脂质氧化通常伴随着质量的损失，因为在这个过程中会损失有营养价值的脂质，如多不饱和脂肪酸。此外，由于一些脂质氧化产物具有不利的生物活性，因此在食品中不受欢迎，因此对食品安全也有影响。其中，环氧脂肪酸是最重要的二次脂质氧化产物之一，从定量的角度来看也是如此。在食品中，它们通常以环氧改性脂肪酸链的形式酯化成三酰基甘油。由于食品中氧化油脂组分结构复杂且缺乏实验参考数据，环氧改性甘油三酯的分析仍然面临着很大的挑战。因此，环氧脂肪酸的（定量）分析基本上是在环氧脂肪酸链从甘油骨架中解放出来后的脂肪酸水平上实现的。然而，在这个过程中，重要的结构信息（例如关于环氧脂肪酸在甘油主链上的位置）丢失了，这些信息对了解生物活性、形成和减缓策略很重要。该项目的目标是阐明氧化条件和脂质结构对三酰甘油结合环氧脂肪酸的形成和积累的影响，并结合新获得的实验参考数据，实现对食品中这些化合物的结构精细分析。为此，我们将合成bbbb40环氧改性三酰基甘油，并通过色谱、质谱和核磁共振光谱（Aim 1）对其进行全面表征。在对氧化敏感的参考甘油三酯的广泛培养实验中，在有利于自氧化或光氧化的条件下，将研究不同氧化条件对环氧改性形成和积累的影响。此外，通过在这些实验中使用不同结构的三酰甘油，例如，将不稳定的脂肪酸链酯化到三酰甘油的外部sn-1/3或内部sn-2位置，也将评估脂质结构的影响，并阐明不同条件下环氧改性的主要形成机制（目的2）。最后，利用参考化合物合成和培养实验的数据，我们将分析环氧改性三酰基甘油，并评估一组富含脂质的食品中的模式（目标3）。该项目将为研究界提供分析环氧改性三酰基甘油所需的参考数据，并将大大提高我们对这些化合物及其在食品中的分析的认识。

Lipid oxidation in food frequently comes with quality loss, as nutritionally valuable lipids such as polyunsaturated fatty acids can be lost in the process. In addition, there are implications for food safety since some lipid oxidation products have unfavorable bioactivities and are undesired in food. Amongst these, epoxy fatty acids are one of the most important secondary lipid oxidation products, also from a quantitative point of view. In food, they are usually occurring esterified to triacylglycerol as an epoxy-modified fatty acid chain. Due to the high structural complexity of the oxidized lipid fraction in food and largely absent experimental reference data the analysis of epoxy modified triacylglycerol still comes with significant challenges. Therefore, the (quantitative) analysis of epoxy fatty acids is by and large achieved on the fatty acid level after liberation of the epoxy fatty acid chains from the glycerol backbones instead. However, in this process important structural information (for example about the position of the epoxy fatty acid on the glycerol backbone), with importance to understand bioactivities, formation and hence mitigation strategies, are lost. The goal of this project is to elucidate the impact of oxidation conditions and lipid structures on the formation and accumulation of triacylglycerol-bound epoxy fatty acids and, together with newly acquired experimental reference data, achieve a structurally refined analysis of these compounds in food. For this purpose, >40 epoxy-modified triacylglycerols will by synthesized and characterized thoroughly by chromatography, mass spectrometry and NMR spectroscopy (Aim 1). In extensive incubation experiments with oxidation-susceptible reference triacylglycerols, under conditions favouring autoxidation or photooxygenation, the impact of different oxidation conditions on the formation and accumulation of epoxy modifications will be investigated. Furthermore, by employing structurally different triacylglycerols in these experiments, e.g., with the labile fatty acid chain esterified to the outer sn-1/3 or the inner sn-2 position of the triacylglycerol, the impact of lipid structures will be assessed as well and the principal formation mechanism of the epoxy modification in different conditions elucidated (Aim 2). Finally, using the data from reference compound synthesis and incubation experiments we will analyse epoxy-modified triacylglycerols and evaluate the patterns in a set of lipid rich food items (Aim 3). This project will provide the research community with the required reference data for analysis of epoxy-modified triacylglycerols and will significantly improve our understanding about these compounds and their analysis in food.