An enzymatic reaction might be the major cause of color reversion in soybean oil. During the soybean flaking process, enzymatic reactions take place to convertγ‐tocopherol to 5‐(tocopheryloxy)‐γ‐tocopherol (γ‐TED), and then further convertγ‐TED to the precursors which are the cause of color reversion. The variations ofγ‐tocopherol andγ‐TED contents in soybean oil are accompanied by an inverse change in the precursors’ concentration. Therefore, the contents ofγ‐tocopherol orγ‐TED in crude soybean oil could be used as an index for predicting the color quality (color reversion) of soybean salad oil. Almost all the precursors (such as tocored) were converted to color‐reverted substances under catalysis after bleaching treatment, and they were converted back to the precursors during deodorization. Those precursors might be gradually reconverted into the color reverted substances during storage to cause the color reversion in soybean salad oil.

Color reversion in soybean oil can be prevented by reducting the enzyme activity of soybeans before cracking and flaking. Soybean oil extracted from steamed, intact soybeans (18% moisture) had lower Rm (max. red) values in RBD oil, higher amounts of γ‐tocopherol, plus its isomers, in both crude and RBD oil, and also higher amounts of hydratable phosphatides in crude oil than those in the oils from the same beans without steam treatment. For soybean pretreatments, a toasting process is less effective than the steaming process for the inhibition of color reversion of soybean oil. To prevent the occurrence of color reversion in RBD soybean oil, the amount of γ‐tocopherol and γ‐TED (5‐[tocopheryloxy]‐γ‐tocopherol) should be above 550 ppm in crude oil.