| ?-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-purity?-tocopherol,and to evaluate the antioxidative activity of?-and?-,?-tocopherol at different temperatures and dosages.In addition,the conversion products of?-tocopherol in heating oil system were separated,purified and identified.Firstly,?-tocopherol of high purity was obtained from VE?90%of total tocopherol content in VE?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 of?-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 of?-tocopherol were?98.89±0.68?%and?93.23±0.89?%,respectively.Secondly,the abilities of?-tocopherol to chelate Fe2+and scavenge DPPH free radicals were compared to definite the antioxidative way of?-tocopherol.And the effects of?-,?-,and?-tocopherol dosages on oxidation stability of lard at different temperatures were evaluated using Rancimat method.Results showed that?-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 that?-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 was?->?->?-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,?-tocopherol had the best antioxidant effect,followed by?-tocopherol,and?-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 order?->?->?-tocopherol.Particularly,when the concentration of?-tocopherol in lard was more than 1000 mg/kg at 110°C,the antioxidative effect of?-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 of?-tocopherolThirdly,the antioxidative activity of?-tocopherol decreased and even?-tocopherol promoted the oxidation of lard when its initial concentration was more than 1000 mg/kg.These might be that the conversion products of?-tocopherol had a negative effect on the antioxidant effect of?-tocopherol.Two major conversion products of?-tocopherol from the heating oil were separated,purified and identified with HPLC,Prep-LC,MS and NMR technologies,and these two conversion products were?-tocopherol Quinone??-tocored?and6-?3-hydroxy-3,7,11,15-tetramethylhexadecyl?-3,4-dimethy lcyclohexa-3,5-diene-1,2-dione. |
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