Stability of α‐, γ‐, or δ‐Tocopherol during Soybean Oil Oxidation

ABSTRACT: The decomposition of α‐, γ‐, or δ‐tocopherol in soybean oil during 24 d of storage at 50 °C was determined by high performance liquid chromatography (HPLC). The initial contents of α‐, γ‐, and δ‐tocopherol in soybean oil were 53, 750, and 268 ppm, respectively. The degradation rates of α‐, γ‐, and δ‐tocopherol for the first 10 d were 5.6%, 1.2, and 0.5% per day, respectively. The α‐tocopherol was completely destroyed in 16 d. The destructions of γ‐ and δ‐tocopherol were 28% and 17% after 24 d. The induction period of soybean oil determined by headspace oxygen, conjugated diene, and peroxide value was 8 d. As the degradations of α‐, γ‐, and δ‐tocopherol increased, the headspace oxygen disappearance, conjugated diene formation, and peroxide value of soybean oil increased. The correlation coefficient between the degradation of tocopherols and the oxidation of soybean oil was about 0.95. The degradation of tocopherols in soybean oil during storage was due to the oxidation.