Studies of Rapid Determination of Vitamin E and Its Application on Natural Foodstuffs

Abstract

The purpose of this study is to establish a rapid and exact method for the determination of tocopherols, and to estimate the tocopherol contents of common foods in Taiwan by the established method. I. Establishment of tocopherol analysis The analytical methods of tocopherols,including spectrophotometry,thin layer chromatography,gas chromatography and high performance liquid chromatography (HPLC),were evaluated.The tocopherol standards included α-,β-,γ-, and δ- tocopherol. Among these methods, the normal phase HPLC performed by the conditions as follows: column, Develosil SI60-5 (4.6 x 250mm); eluent, n-hexane:dioxane: ethanol (958:40:2, v/v/v)flow rate, 1ml/min;detector, UV 298nm was the best one for the tocopherol determination because of its good calibration, reproducibility,resolution and short time analysis. II. Quantitative determination of tocopherols in foods The investigated food materials included 48 common food samples in Taiwan and 5 capsule samples containing natural vitamin E. The food material was saponified with potassium hydroxide, then extracted with n-hexane and concentrated under nitrogen gas. The residue, dissolved in n-hexane to adjust an appropriate concentration, was prepared for the HPLC analysis. The sample was examined for the contents ofα-,β-,γ-, and δ-tocopherol, and therefore the vitamin E potency could be calculated. Among these food samples ,oils, legumes seeds , nuts,wheat germ , Oolong tea and Chiann-Shyr(seeds of Euryale ferox Salisb. ) showed a high tocopherol content. The foods showing a high α-tocopherol content were Oolong tea 46.2, Chiann-Shyr 41.6 , sunflower oil 27.2 , wheat germ , peanut 11.2, soybeanoil 10.2 , palm oil 8.5 and peanut oil 5.8mg/100g. The foods with a high content ofγ-tocopherol were soybean oil 78.5, sesame oil 43.2, sesame seed 22.7 , soybean 12.5, black bean 12.2 and peanut 7.2mg/100g. The contents ofβ-tocopherol on Chiann-Shyr and wheat germ were 18.1 and 9.8mg/100g. The vitamin E potency in the capsules of vitamin E and lecithin was 14.3-15.9 , or 5.2-5.9mg/100g respectively.