Antioxidant activity of vitamin E enhanced by cyclodextrin inclusion complex

Purpose The study aims to find potential method to enhance the stability and antioxidant activity of vitamins. Design/methodology/approach Vitamin E (VE) and beta-cyclodextrin (CD) were used to prepare the VE-beta-CD inclusion complex via a solution method. The yielded VE-beta-CD obtained from optimal experimental conditions was characterized. The mechanism of complex formation and the properties of the complex was investigated by steady-state and time-resolved fluorescence techniques. The antioxidant activity of VE-beta-CD was evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and compared with pure VE. Findings Three experimental factors - reaction temperature (T), molar ratio of VE to beta-CD (rm) and inclusion time (t) - were studied for the preparation of VE-beta-CD. At experimental conditions of T = 60 degrees C, rm = 1:3 and t = 3 h, a maximum inclusion rate of VE (78.62%) was obtained. The Fourier-transform infrared spectroscopy (FTIR) shows that VE molecule was physically encapsulated by beta-CD in the yielded product. Subsequentially, the steady-state fluorescence intensity of VE was found to increase upon encapsulation by beta-CD due to the hindrance of fluorescence quenching of VE molecules inside the hydrophobic cavity of beta-CD, and an inclusion constant K was determined to equal 3.58 x 103 L/mol from the fluorescence results. The fluorescent observation was confirmed by time-resolved fluorescence experiment as the lifetime of VE increased with an increase in beta-CD concentration. Originality/value The ability of removing radicals by VE was significantly enhanced after the formation of inclusion complex with beta-CD.