1 Introduction
Natural standard grade γ-tocopherol are of great interest due to its good antioxidant activity and special pharmacological functions. For instance, high-purity natural γ-tocopherol can significantly decrease tumor multiplicity induced by AOM, while mixed tocopherols cannot (Jiang et al. 2013). γ-tocopherol was also found to be able to induce the apoptosis of colorectal cancer cells in comparison to α-tocopherol when used in conjunction with lovastatin (Braunrath et al. 2010). In addition, γ-tocopherol can protect edible oil and oil-rich foods from oxidization (Braunrath et al. 2010; Broznić et al. 2016). However, at present, high-purity natural γ-tocopherol is mainly sold in the form of standard at a high price (20000 RMB/g, Sigma) indicating the short of mature and economically feasible γ-tocopherol production method. Therefore, it is of great necessity to find an economically feasible method to obtain natural standard grade γ-tocopherol.
Currently, numerous studies focused on obtaining mixed tocopherol from deodorizing distillate (Hiromori et al. 2016; Ito et al. 2007; Zhou et al. 2009). Few studies paid attention to the separation and purification of γ-tocopherol. Tocopherol monomers was separated from soybean Vitamin E concentrate using low-pressure column chromatography with cyclohexane-ethanol as eluent (Wan et al. 2008). Under optimal operating conditions, the purity of γ-tocopherol was increased from 31.6% to 91.23%. Nevertheless, the purity of γ-tocopherol was not up to the standard grade and its recovery was only about 30%. A semi-prepared liquid chromatography method has been developed to separate four tocopherol monomers from the mixture of soybean oil and wheat germ oil (Tai-Sun and Godber 1994). γ-tocopherol could be well separated from α-, β- and δ-tocopherol and the purity of γ-tocopherol were around 99% (Tai-Sun and Godber 1994). But this method used toxic tetrahydrofuran which is not eco-friendly (Joshi and Adhikari 2019). The mass of separation was so small that only 28.8 mg samples can be isolated at one time suggesting that this method was not suitable for the plant scale. Therefore, further studies are required to shed light on this issue.
This study intended to prepare natural standard grade γ-tocopherol using eco-friendly and low toxicity solvents (n-hexane, ethyl acetate). The adsorption behavior of γ-tocopherol on silica gel was discussed, which provided numerical support for the preparation of high-purity γ-tocopherol. Additionally, we compared the antioxidant activity of the purified γ-tocopherol with α- and δ-tocopherol using lard as model fat.
2 Materials and methods