Grease color change in the use, called in the industry grease anti-color or back color. In general, the anti-color does not affect its food value.
Effect of vegetable color reversion many factors: pigment, metal ions, light, oxygen, temperature, natural antioxidants (tocopherol) oxides, fatty acid oxides.
On the one hand, corn oil is a byproduct of corn deep processing, the process is much more complicated than soybean oil, crude corn oil have high acid, impurities, the iron ions are also much higher than soybean oil, if refined removal is not complete, it is easy to lead to poor quality stability, iron ions itself is not harmful, but having a catalytic activity, can accelerate fat oxidation and rancidity and other metamorphic processes.
On the other hand, corn germ oil, unsaturated fatty acids, high tocopherol content of the oil as the main features of the health indicators, are more prone to reversion phenomenon, usually around 32 degrees in summer temperatures, oil color changes difference within 3 days is very significant.