Effects of moisture content and presence of γ-tocopherol on the stability of α-tocopherol in stripped corn oils

The stability of α-tocopherol in stripped corn oils with or without added γ-tocopherol was determined under different levels of relative humidity (RH) ranging from 0 to 93% at 60°C. The degree of oxidation was determined by the headspace oxygen content and conjugated dienoic acid (CDA) assays and the remaining α- and γ-tocopherols were also analyzed. The stability of α-tocopherol was significantly influenced by the presence of moisture, the concentration of α-tocopherol, and the presence of γ-tocopherol. Samples containing up to 100 ppm α-tocopherol showed the lowest stability under 75% RH whereas those containing 200 ppm α-tocopherol had the highest stability under 93% RH. Samples under 0% RH had the lowest α-tocopherol stability in the presence of γ-tocopherol. Generally, higher concentrations of γ-tocopherol resulted in the retention of more α-tocopherol in stripped bulk oils. Practical application: Tocopherol isomers are typical lipophilic antioxidants in oils. Many lipid-rich foods contain tocopherol isomers to extend the shelf-life of the products. The stability of α-tocopherol was significantly influenced by the presence of moisture, the concentration of α-tocopherol, and the presence of γ-tocopherol. Generally, higher concentrations of γ-tocopherol resulted in the retention of more α-tocopherol in stripped bulk oils. Using the knowledge obtained in this study, shelf-life of foods containing oils can be enhanced by modifying the moisture content and concentration and types of tocol isomers. Generally, α-tocopherol and γ-tocopherol were more stable at RH 32% and RH 75%, respectively in stripped bulk oils.