Kamgang Nzekoue Franks, Henle Thomas, Caprioli Giovanni, Sagratini Gianni, Hellwig Michael
School of Pharmacy, University of Camerino, Via Sant Agostino 1, 62032 Camerino, Italy.
Chair of Food Chemistry, Technische Universität Dresden, 01062 Dresden, Germany.
Foods. 2020 Dec 17;9(12):1882. doi: 10.3390/foods9121882.
Sterols, especially cholesterol and phytosterols, are important components of food lipids. During food processing, such as heating, sterols, like unsaturated fatty acids, can be oxidized. Protein modification by secondary products of lipid peroxidation has recently been demonstrated in food through a process called lipation. Similarly, this study was performed to assess, for the first time, the possibility of reactions between food proteins and sterol oxidation products in conditions relevant for food processing. Therefore, reaction models consisting of oxysterol (cholesterol 5α,6α-epoxide) and reactive amino acids (arginine, lysine, and methionine) were incubated in various conditions of concentration (0-8 mM), time (0-120 min), and temperature (30-180 °C). The identification of lysine adducts through thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC) with a diode array detector (DAD), and electrospray ionization (ESI) mass spectrometry (MS) evidenced a reaction with lysine. Moreover, the HPLC-ESI with tandem mass spectrometry (MS/MS) analyses allowed observation of the compound, whose mass to charge ratio 710.5 and fragmentation patterns corresponded to the reaction product [M + H] between cholesterol-5α,6α-epoxide and the ε-amino-group of N-benzoylglycyl-l-lysine. Moreover, kinetic studies between N-benzoylglycyl-l-lysine as a model for protein-bound lysine and cholesterol 5α,6α-epoxide were performed, showing that the formation of lysine adducts strongly increases with time, temperature, and oxysterol level. This preliminary study suggests that in conditions commonly reached during food processing, sterol oxidation products could react covalently with protein-bound lysine, causing protein modifications.
甾醇，尤其是胆固醇和植物甾醇，是食物脂质的重要组成部分。在食品加工过程中，如加热时，甾醇与不饱和脂肪酸一样，会被氧化。最近在食品中通过一种称为脂化的过程证明了脂质过氧化的次级产物会对蛋白质进行修饰。同样，本研究首次评估了在与食品加工相关的条件下，食品蛋白质与甾醇氧化产物之间发生反应的可能性。因此，将由氧甾醇（胆固醇5α,6α-环氧化物）和活性氨基酸（精氨酸、赖氨酸和蛋氨酸）组成的反应模型在不同的浓度（0 - 8 mM）、时间（0 - 120分钟）和温度（30 - 180°C）条件下进行孵育。通过薄层色谱（TLC）、配备二极管阵列检测器（DAD）的高效液相色谱（HPLC）以及电喷雾电离（ESI）质谱（MS）对赖氨酸加合物的鉴定证明了其与赖氨酸发生了反应。此外，通过HPLC - ESI串联质谱（MS/MS）分析观察到了该化合物，其质荷比为710.5且裂解模式与胆固醇 - 5α,6α - 环氧化物和N - 苯甲酰甘氨酰 - L - 赖氨酸的ε - 氨基之间的反应产物[M + H]相对应。此外，还对作为蛋白质结合赖氨酸模型的N - 苯甲酰甘氨酰 - L - 赖氨酸与胆固醇5α,6α - 环氧化物之间进行了动力学研究，结果表明赖氨酸加合物的形成会随着时间、温度和氧甾醇水平的升高而显著增加。这项初步研究表明，在食品加工过程中通常会达到的条件下，甾醇氧化产物可能会与蛋白质结合的赖氨酸发生共价反应，从而导致蛋白质修饰。
