Effect of Randomization on the oxidative stability of corn oil

Randomized corn oil TAG oxidized much faster than natural oil, but after purification with alumina, they oxidized at the same rate. We showed that this effect could not be attributed to a difference in total tocopherols in the randomized and natural oils. Polar material recovered from the alumina treatment was fractionated by TLC, and a pro-oxidant effect was found in the fractions containing MAG and DAG. However, MAG and DAG, although mild pro-oxidants, could not account for the prooxidant effect generated by randomization. No other compounds could be detected in the MAG fraction by MS. The pro-oxidant effect of randomized oil disappeared when EDTA or citric acid was added in sufficient amounts. The pro-oxidant effect of randomized corn oil was increased by the incorporation of additional copper or iron at a concentration that did not catalyze oxidation of the purified oil. Treatment of corn oil with ascorbic acid, ascorbyl-6-palmitate, ethyl acetoacetate, ethyl diacetoacetate, and acetylacetone did not reproduce the effect of the unknown pro-oxidant. Although the identity of the pro-oxidant is still unknown, we have confirmed that it is produced during randomization; it does not have pro-oxidant activity alone, but it facilitates the catalytic activity of the transition metal ions.