## 4 Discussion
[PERSON] pointed out that the changes in the viscosity of an oil during heating can be expected to depend on products generated during frying and differing in molecular size from triacylglycerols (i.e., oxidation, polymerization, hydrolysis, and fission products) [46]. [PERSON] showed that when the oil is heated at high temperatures and is oxidized to form a polymer with a high molecular weight, viscosity increases as the amount of the polymer increases. Therefore, the higher the viscosity of frying oil, the more oxidation can be generally expected [47]. Overall, the principle of the increase in viscosity during oil oxidation is due to the interaction between oxidation products and original molecules in the oil, forming longer molecular chains, polymers, and colloids, which increase the mutual attractive force between oil molecules. Unsaturated esters are less viscous, and they quickly oxidize, whereas saturated esters have a high cloud point and high viscosity [48]. The preponderance of saturated fatty acids restricts the flow of oil. Therefore, the level of oxidation rises and the viscosity of the oil increases. In addition, it is well known that oils deteriorate due to the effects of heating and oxidation [49]. This deterioration is accompanied by odours that worsen the cooking environment. Edible oil degradation frequently produces disagreeable flavours [50]. By monitoring the change of volatile lipid oxidation products and proton peaks at the reactive sites of lipid molecules during the oxidation process, GC-MS and \({}^{1}\)H-NMR can assess the oxidation state of lipids, because the oxidation of unsaturated fatty acids is accompanied by volatile lipid oxidation products and a series of changes in hydrogen atoms in different chemical environments [51]. Foods frequently contain lecithin, which has many beneficial functions such as emulsification, crystallization inhibition, non-stick releasing agents, wetting agents, and anti-sputtering agents [52]. Lecithin may enhance the transport of polyphenols, which leads to increased antioxidant activity [19]. [PERSON] showed that the addition of lecithin improved the dispersion and stability of phenolic extracts in olive oil, thus enhancing the oxidation stability of concentrated oil [53]. [PERSON] found that soybean lecithin increased the solubility of quercetin and could improve the antioxidant effect of sunflower seed oil [54]. [PERSON] also pointed out that the solubility and antioxidant activity of epigallocatechin gallate in lipids can be enhanced through the carrier system or esterification with aliphatic acyl derivatives [20]. In the study, lecithin was added to the Aoil, which lead to the increase of the solubility of CA in the oil, and thus improves the protective effect of CA on the Aoil, and Aoil was supplemented with the highest amount of lecithin (20 mg/g oil) that could be dissolved in the oil [29]. In the future, the stability of Aoil will be tested using various concentrations of lecithin, applied in varying proportions. Lecithin is sometimes used as an antioxidant in foods. Several mechanisms of how lecithin could influence lipid oxidation have been proposed. In general, lecithin could bind prooxidative metals, produce antioxidative compounds through Maillard reactions during lipid oxidation, alter the location of other antioxidants [55], and regenerate primary antioxidants such as tocopherols [56]. However, lecithin could also serve as oxidation substrates themselves. Owing to their high degree of unsaturation, negative charges that attract prooxidant metals, and large surface area when they exist as dispersions, they can be an important substrate for oxidation in foods containing considerable amounts of biological membranes, such as meats [57]. In addition, there were also times when lecithin showed no antioxidant activity or even acted as prooxidants [58]. One possible prooxidant mechanism of phospholipids in bulk oil could be their formation of association colloids, such as reverse micelles, which can increase metal-lipid interactions [59].