Improving stabilization of α-tocopherol and α-tocopheryl acetate against oxidation, light and UV radiation by complexation with β-cyclodextrin and starch

Despite the remarkably high antioxidant activity of tocopherols, their applications in the food industry are limited because of their instability under various conditions. Complexes of α-tocopherol (α-TQ) or α-tocopheryl acetate (α-TQA) with β-cyclodextrin (β-CD) or starch were prepared and characterized by UV–vis, IR and thermal analysis. Oxidative stability of α-TQ and α-TQA against H₂O₂ was 74.7 and 88.8% respectively (576 h). However, stability increased to 82.9 and 100% for β-CD and 99.2 and 99.4% for starch complexes respectively, which indicates that starch is an excellent stabilizing host in addition to being an economic material. Stability of α-TQ and α-TQA under light conditions was dependent on their physical state; it was 55.3 and 82.9% (oil) but stability was lowered to 19.4 and 76.5% in solution (2.21 mM). In addition, exposure to UV irradiation decreased their stability to 39.2 and 85.0% as oil and 61.2 and 89.1% in solution respectively. However, the stability of all complexes remained > 99.0% under light and UV conditions. Accordingly, α-TQ, the natural and biologically active form, can be used as complex rather than α-TQA often used because of its higher stability. Docking revealed that both forms fit in β-CD with the side chain taking “U” conformation.