Sunflower oil (SO) and extra virgin olive oil (EVOO) were heated at 90 °C in the presence of PBN. The radical species formed during thermal treatment, trapped by PBN, were revealed by electron paramagnetic resonance (EPR) spectroscopy, a widely used method to study the oils’ oxidation. The effect of the experimental parameters on the intensity of PBN adduct was analyzed with the aim to standardize the spin trapping protocol for oils. A modification of the Boltzmann sigmoidal equation was proposed to fit the experimental points representing the changes of the EPR intensity of the PBN adduct versus time. The fitting parameters allowed for distinguishing between SO and EVOO and to obtain more reliable induction period (IP) values. The fitting parameters and the shape of the curve depend on the diameter of the sample holder. The IP and the time at which maximum intensity is reached, t(I_max) in thin capillary tubes (IP 35.92 min, t(I_max) 186 min) were shifted at longer times in comparison with flat cell (IP 69.54 min, t(I_max) 106 min). The peroxide values (PV) were measured in SO and EVOO samples with and without PBN at specific points of the curve and related to the intensity of the EPR signals. PBN inhibits the propagation of the chain reaction, and the extent of inhibition is lower in EVOO than in SO possibly due to the effect of phenolic compounds that in SO are lacking. The phenolic compounds are also responsible for the lower PBN adduct intensities observed in EVOO than in SO. This study further highlights the power of EPR spectroscopy in the evaluation of oil oxidation and provides a guide for EPR experimental and fitting parameters for oils.

中文翻译：

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向日葵油和橄榄油热处理的电子顺磁共振自旋捕获：实验和拟合参数的优化

在 PBN 存在下，向日葵油 (SO) 和特级初榨橄榄油 (EVOO) 在 90 °C 下加热。热处理过程中形成的自由基物种被 PBN 捕获，通过电子顺磁共振 (EPR) 光谱揭示，这是一种广泛使用的研究油氧化的方法。分析了实验参数对 PBN 加合物强度的影响，目的是标准化油的自旋捕集协议。提出了对玻尔兹曼 sigmoidal 方程的修改，以拟合代表 PBN 加合物 EPR 强度随时间变化的实验点。拟合参数允许区分 SO 和 EVOO 并获得更可靠的诱导期 (IP) 值。拟合参数和曲线形状取决于样品架的直径。t ( I _max ) 在细毛细管中 (IP 35.92 min, t ( I _max ) 186 min) 与扁平细胞 (IP 69.54 min, t ( I _{max )}) 106 分钟)。过氧化值 (PV) 在 SO 和 EVOO 样品中测量，在曲线的特定点有和没有 PBN，并且与 EPR 信号的强度有关。PBN 抑制链式反应的传播，EVOO 中的抑制程度低于 SO，可能是由于 SO 中缺乏酚类化合物的作用。酚类化合物也是导致在 EVOO 中观察到的 PBN 加合物强度低于 SO 的原因。这项研究进一步突出了 EPR 光谱在评估油氧化方面的能力，并为油的 EPR 实验和拟合参数提供了指导。