## 2 Results
### GC-MS Studies of Fatty Acids Produced in Soybean Oil at the End of Accelerated Oxidation  
This study involved analyses with different antioxidants (200 ppm QG, PG, BHT and TP) used to treat soybean oil. The fatty acid profiles of the analysed oils are shown in Table 3. Fourteen fatty acids (six saturated and eight unsaturated) were identified in total. The main unsaturated fatty acids (UFAs) were C18:1 (oleic acid) and C18:2 (linoleic acid). The saturated fatty acids were C10:0 (capric acid), C16:0 (palmitic acid), C18:0 (stearic acid), C20:0 (methyl arachid) and C22:0 (behenic acid). Then, the data for total fatty acids (TFAs) were imported into the MetaboAnalyst 5.0 for further analyses, including PCA and PLS-DA. The PCA and PLS-DA results are shown in Figure 4a,b. PCA and PLS-AD showed good duplication within groups and significant differences among the five different groups of soybean oil samples. Figure 4c and Table 4 show the total amounts of saturated fatty acids (SFAs), unsaturated fatty acids (UFAs) and the ratio between unsaturated and saturated fatty acids (UFA/SFA) for the soybean oils analysed. The analytical results for fatty acid composition showed that the QG group had the highest proportion of unsaturated fatty acids, followed by the PG group, whereas the proportion of unsaturated fatty acids in TP was the lowest among the five groups. PG and QG had the highest proportions of UFAs, approximately 84.67% \(\pm\) 0.33% and 82.94% \(\pm\) 0.65% of total fatty acids (TFAs), respectively. Moreover, the UFA/SFA ratios were highest for the PG and QG groups and measured approximately 5.53 \(\pm\) 0.14 and 4.87 \(\pm\) 0.22, respectively. In contrast, there was no significant difference between the TP group and the CK group. The analytical results presented in Figure 4d and Table 4 showed that eight unsaturated fatty acids were detected in soybean oil, of which (9E,11E)-9,11-octadecadienoic acid exhibited the highest content, and the contents of the PG and QG groups were the highest and roughly five times more than that of the CK group. Otherwise, elaidic acid constituted a high proportion of unsaturated fatty acids but was only detected in the PG, QG and BHT groups. The above results showed that it is important to delay the oxidative rancidity of soybean oil and inhibit the oxidation of oleic acid and linoleic acid in unsaturated fatty acids, especially (9E,11E)-9,11-octadecadienoic acid and elaidic acid. Oxidation of QG during the process of delaying soybean oil oxidative rancidity provided a good antioxidant effect, which was significantly better than those for the positive controls BHT and TP but slightly weaker than that for PG. Moreover, the results showed the same trend seen for the peroxide values and acid values. Figure 3: Mean peroxide value (PV) for pure soybean oil and oil treated with different concentrations (100, 200, 400, 800 and 1600 ppm) QG (**A**); mean peroxide value (PV) for pure soybean oil, QG and positive antioxidants with 200 ppm (**B**); mean acid value (AV) for pure soybean oil, QG and positive antioxidants with 200 ppm (**C**); mean PV in soybean oil treated with different concentrations QG after 56 days (**D**); mean PV in soybean oil treated with different antioxidants after 56 days (**E**); mean AV in soybean oil treated with different antioxidants after 56 days (**F**). Error bars represent the mean value \(\pm\) SD. Significant differences between diet groups at the indicated week are signified by letters, where different letters indicate difference (\(p<0.05\)) between groups, while the same letter indicates no difference. Figure 4: Fatty acid composition of oil treated with different antioxidants: PCA score plot **(a)**; PLS-DA score plot **(b)**; mean peak area of saturated fatty acids (SFAs) and unsaturated fatty acids (UFAs) **(c)**; mean peak area of various unsaturated fatty acid **(d)**.