Regarding the stability of tocopherol, for pure soybean oil at high temperature, the literature suggests the following
stability sequence: d > g > b > a (Kamal-Eldin and Appelqvist 1996). However, we found that, soybean oil
free from antioxidants, stability decreased in the order d > b > a=g. Steel et al. (2005) also found a greater degradation
of a and g-tocopherol in soybean oil that had been heated for 10 h. A rapid degradation of a-tocopherol was reported by Verleyen (2001). Furthermore, Warner and Gehring (2009) observed a higher degradation of a- and d-tocopherol in soybean oil subjected to 65 h of frying.