An oil sample was prepared by cold-pressing from untreated (UTRO) and microwave-treated (MWRO) rapeseed, and tertiary butyl-hydroquinone (TBHQ) was added to another oil from untreated rapeseed. Microwave pretreatment significantly increased the total phenolics and canolol contents, as well as the initial acid value (AV), peroxide value (PV), and p-anisidine value (pAV) of oil (p<0.001). However, there was found to be a difference in the rate of increase of AV, PV, and pAV of oil during the autoxidation with the following order of all these values observed: UTRO > UTRO + TBHQ > MWRO. During storage, significant linear correlations (p<0.001) were found between the PV, pAV, and canolol content (PV vs. Canolol = −0.960 to −0.890; pAV vs. Canolol = −0.889 to −0.968), and the DPPH activity was also linearly and significantly correlated with the content of total phenolics and canolol in oils. (DPPH vs. Tatal phenolics = 0.910–0.945; DPPH vs. Canolol = 0.941–0.962; p<0.001). When the autoxidation test was completed (on the 10th wk), it was found that the contents of canolol and total phenolics in MWRO were the highest, followed by UTRO + TBHQ, and UTRO. These results indicate that the MWRO exhibited superior oxidative stability.
Practical application: Canolol, also known as vinylsyringol, is a phenolic compound that has been identified as a decarboxylation product of sinapic acid, and this type of compounds is known for scavenging free radicals. In this study, we evaluated the changes occurring during storage in the contents of canolol and the total phenolics, oxidative stability, and antioxidant capacity of rapeseed oil and found good correlation among the canolol content, oxidative stability, and antioxidant capacity. Therefore, we can use canolol as a native antioxidant for rapeseed oil production in the future.
Canolol in rapeseed and rapeseed oil that is formed by thermal decarboxylation of sinapic acid under microwave irradiation. Canolol formation has been shown to improve the oxidative stability of oil from microtreated rapeseed. The results showed a very good correlation between the level of primary oxidative products (peroxide values), secondary oxidative products (p-anisidine values) and the contents of canolol in the rapeseed oil during storage. So, canolol has potential applications in oil storage.