Date of Award
Doctor of Philosophy
Food Science and Human Nutrition
Earl G. Hammond
The oxidative stability of natural and randomized corn oil was studied at high temperature (80 or 100°C) by using an OSI (oxidative stability instrument) and at low temperature (28, 40 or 50°C) by using peroxide values determined by the ferrous iron oxidation test. Randomized corn oil without purification oxidized 1 to 5 times faster than did natural corn oil, depending on the particular lot of corn oil. After alumina-column purification, which removed the tocopherols and other polar compounds, there was no difference in the oxidation rates of the randomized and natural corn oil. These findings suggest that alteration of the glyceride structure had no effect on the oxidation rate of corn oil triaclyglycerol (TAG), and that a prooxidant was produced during randomization that can be removed by alumina purification.;The prooxidant had polarity similar to monoacylglycerol (MAG) and diacylglycerol (DAG) on TLC (thin layer chromatography) plates. Synthetic linoleate MAG and DAG showed a slight prooxidant effect in purified corn oil at >0.25% for MAG and >5% for DAG, but had no prooxidant effect at similar levels in unpurified oil. The prooxidant effect produced in randomized oil could be greatly increased by trace amounts of cupric or ferrous ions. EDTA and citric acid effectively restored the oxidative stability of the randomized corn oil, but an adsorptive bleaching treatment made the prooxidant problem even worse.;These results suggest that the prooxidant formed during randomization may facilitate the catalytic activity of transition metals in oil oxidation. Therefore, precautions should be taken when using interesterification or randomization processes in the food industry. Purification may be needed to remove the prooxidant and metal ions, or EDTA or citric acid could be added to prevent the prooxidant activity.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu
Jiang, Yongzhi, "Effect of randomization on the oxidative stability of corn oil " (2004). Retrospective Theses and Dissertations. 1172.