The present study investigated the lipid oxidation degree of soybean oil during regularly discontinuous 40 h-deep-frying process. Electron spin resonance (ESR) spectroscopy technique was applied to identify and quantify the formed radicals, along with evaluation of physicochemical parameters including acid value (AV), peroxide value (PV), p-anisidine value (p-AnV), polar compounds (PC), fatty acid composition and volatile profile. Results showed the AV, p-AnV, PC and free radical of frying oil samples increased significantly with the increasing frying time. The results of fatty acids showed that unsaturated fatty acid such as C18:1 and C18:2 decreased by 19.98% and 14.58%, respectively, with prolonged frying time, while the content of C16:1, trans C18:1 and C18:2 increased by 20.38%, 425% and 42.86%, respectively, when compared to the fresh oil samples. In contrast, the content of saturated fatty acid had little change. In total, 37 volatile compounds were detected revealing a complex aroma profile of frying soybean oil, composed of 15 aldehydes, 8 alcohols, 4 ketones, 4 acids, 5 alkanes and 1 furan. Principal component analysis and hierarchical clustering analysis indicated that hexanal, heptanal, (E)-2-hexenal, octanal, (E)-2-heptenal, nonanal, (E)-2-octenal, undecanal, (E,E)-2,4-heptadienal, (E)-2-decenal, 2-undecenal, (E,E)-2,4-decadienal, 1-pentanol, 2,2-dimethyl-3-hexanol, (Z)-2-dodecenol, 1-octen-3-ol, pentanoic acid, octanoic acid, nonanoic acid and 2-pentyl-furan may be potential markers for evaluating lipid oxidation of frying soybean oil.

中文翻译：

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油炸大豆油的挥发性成分作为脂质氧化和质量降解的指标

本研究调查了在不连续的40小时油炸过程中豆油的脂质氧化程度。电子自旋共振（ESR）光谱技术用于鉴定和定量形成的自由基，并评估其物理化学参数，包括酸值（AV），过氧化物值（PV），对氨基苯甲酸值（p -AnV），极性化合物（ PC），脂肪酸组成和挥发物分布。结果表明，煎炸油样品的AV，p- AnV，PC和自由基随煎炸时间的增加而显着增加。脂肪酸的结果表明，随着煎炸时间的延长，不饱和脂肪酸（例如C18：1和C18：2）分别下降了19.98％和14.58％，而C16：1，与新鲜油样品相比，反式C18：1和C18：2分别增加了20.38％，425％和42.86％。相反，饱和脂肪酸的含量几乎没有变化。总共检测到37种挥发性化合物，揭示了油炸大豆油的复杂香气，其由15种醛，8种醇，4种酮，4种酸，5种烷烃和1种呋喃组成。主成分分析和层次聚类分析表明，己醛，庚醛，（E）-2-己醛，辛醛，（E）-2-庚醛，壬醛，（E）-2-辛基，十一烷，（E，E）-2 ，4-庚二烯醛，（E）-2-癸烯，2-十一烯醛，（E，E）-2,4-癸二烯醛，1-戊醇，2,2-二甲基-3-己醇，（Z）-2-十二烯醇，1-辛烯-3-醇，戊酸，辛酸，壬酸和2-戊基呋喃可能是评估油炸大豆油脂质氧化的潜在标志物。