Importance of the higher retention of tocopherols and sterols for the oxidative stability of soybean and rapeseed oils.

Tocopherols and sterols were lost considerably during the refining process of vegetable oils, resulting in a dramatic decrease in the oxidation stability. However, the oxidation stability of vegetable oils was not directly proportional to tocopherol content, not mention to its synergistic interaction with sterol. Based on the peroxide values of oils with different content of tocopherols and sterols during storage at 65 °C, it was found that soybean oil (SO) had the best stability when the content of tocopherols and sterols was 0.14 and 1.09%, respectively, whereas the value in rapeseed oil (RO) was 0.06% and 1.14-2.90%. The optimal content of tocopherol in RO was lower than that in SO was due to the different tocopherol isoforms. Furthermore, it was found that the storage stability decreased significantly when adding a same content of α-tocopherol, compared with that by retaining more tocopherol isoforms existed in SO. It was suggested that retaining more tocopherol and sterol during vegetable oils refining improved the oxidation stability, however, it did not mean the more the better. The oxidation stability was dependent on both the content and the isoform. This study helps to define the effective contents of tocopherol and sterol under the moderate refining technology.

Effect of deodorization conditions on fatty acid profile, oxidation products, and lipid-derived free radicals of soybean oil.

Oxidative stability is a key quality characteristic of edible oils, and the oil's antioxidant capacity decreases during the deodorization stage. This study explores the changes in radical formation, molecular structure, oxidative characteristics, fatty acids, and main bioactive compounds in soybean oil during deodorization. The lag phase decreased, whereas the total amount of spins of free radicals increased as the deodorization time increased from 90 to 150 min. The total amount of spins and percentage of alkyl radicals varied dramatically under different times and temperatures (220 âˆ¼ 260 ℃). Results showed that identifying and quantifying the formed radicals can provide useful information for monitoring and controlling oil oxidation in vegetable oil refining systems. Therefore, to control early oxidation events, maximize refined oil product yield, and reduce energy consumption in the refining plant, the priority should be to minimize temperature during the oil refining process and then shorten the deodorization time.