Study On Separation And Purification Of γ-tocopherol And Its Antioxidant Activity

γ-tocopherol is favored by consumers because of its good antioxidant activity and special physiological effects such as anti-cancer and anti-inflammatory properties.This paper sought to optimize the preparation process conditions of high-purityγ-tocopherol,and to evaluate the antioxidative activity ofγ-andα-,δ-tocopherol at different temperatures and dosages.In addition,the conversion products ofγ-tocopherol in heating oil system were separated,purified and identified.Firstly,γ-tocopherol of high purity was obtained from V_E（90%of total tocopherol content in V_E）by one-step column chromatography technology.The influence of eluent type,elution rate,sample loading and ratio of column length to diameter on the recovery and purity ofγ-tocopherol were researched.The optimized conditions were as follows:the eluent solvent was a 94.5:5.5（v/v）mixture of n-hexane and ethyl acetate,the sample volume was0.5g,the ratio of column length to column diameter was 16:1（the amount of silica gel was110g）,and the elution rate was 2 m L/min.Under these conditions,the purity and recovery ofγ-tocopherol were（98.89±0.68）%and（93.23±0.89）%,respectively.Secondly,the abilities ofγ-tocopherol to chelate Fe²⁺and scavenge DPPH free radicals were compared to definite the antioxidative way ofγ-tocopherol.And the effects ofγ-,α-,andδ-tocopherol dosages on oxidation stability of lard at different temperatures were evaluated using Rancimat method.Results showed thatγ-tocopherol had the ability to chelate Fe²⁺and scavenge DPPH free radicals.However,the effect of former was far less than the latter,this meaned thatγ-tocopherol was a good free radical scavenger rather than a metal ion chelator,and the ability of scavenging DPPH free radicals of three tocopherol monomers wasγ->δ->α-tocopherol.The results of Rancimat experiment showed that the anti-oxidative activities of tocopherols were related to the heating temperature and the dosage of tocopherols at 110～140°C.When the tocopherol concentrations in lard was≤1000 mg/kg,γ-tocopherol had the best antioxidant effect,followed byδ-tocopherol,andα-tocopherol was the worst.When the addition of tocopherol was at a high level（2000 mg/kg）,the antioxidative abilities of tocopherols were in the orderδ->γ->α-tocopherol.Particularly,when the concentration ofγ-tocopherol in lard was more than 1000 mg/kg at 110°C,the antioxidative effect ofγ-tocopherol in lard decreased with the increase of added amount.In addition,When the total tocopherols in lard was≤1000 mg/kg,the antioxidant effect of mixed tocopherols was not stronger than that ofγ-tocopherolThirdly,the antioxidative activity ofγ-tocopherol decreased and evenγ-tocopherol promoted the oxidation of lard when its initial concentration was more than 1000 mg/kg.These might be that the conversion products ofγ-tocopherol had a negative effect on the antioxidant effect ofγ-tocopherol.Two major conversion products ofγ-tocopherol from the heating oil were separated,purified and identified with HPLC,Prep-LC,MS and NMR technologies,and these two conversion products wereγ-tocopherol Quinone（γ-tocored）and6-（3-hydroxy-3,7,11,15-tetramethylhexadecyl）-3,4-dimethy lcyclohexa-3,5-diene-1,2-dione.