2001 Volume 27 Issue 1 Pages 76-84
The kinetics of autoxidation of linoleic acid and effect of antioxidants, a-tocopherol and ascorbic acid stearate, on the reaction are investigated in a bubble column type flow reactor. The oxidation of linoleic acid is observed to have two reaction stages, which were an induction period with a slow increase of hydroperoxides and an acceleration period with their rapid increase. The results obtained are analyzed based on a reaction model with radical chain reaction. The rate equation of autoxidation of linoleic acid is formulated as a function of concentrations of linoleic acid and peroxides, partial pressure of oxygen and reaction temperature. The oxidation behavior adding a-tocopherol is found to be markedly different compared with that without a-tocopherol. Three steps during the oxidation which are induction, temporary stable, and accelerated periods are observed. In the induction period, the rate of oxidation is very slow and the maximum effect on the antioxidation is observed at a certain concentration of a-tocopherol. For more than this concentration, the rate increases with increasing in the concentration of a-tocopherol. In the stable period, appropriate formation of peroxide is interrupted and the concentration of peroxides is kept at constant. The time length and concentration of the peroxides in the period increase with increasing concentration of a-tocopherol. In the accelerated period, all of the oxidation rates are very rapid and the same with or without a-tocopherol. By the addition of both a-tocopherol and ascorbic acid stearate the oxidation is effectively suppressed.
