A Rapid Gas Chromatographic Method for Direct Determination of Free Sterols in Animal and Vegetable Fats and Oils
Youk-Meng Choong1*, Hsiu-Jung Lin1, Chung-Wen Chen1 and Mei-Ling Wang2
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Department of Food Sanitation, Ta-Jen Institute of Technology, 20, Wei-Shin Rd., Yan-Puu Hsiang, Pintung Hsien, Taiwan, R.O.C.
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Department of Food Health, Chia-Nan College of Pharmacy and Science, 60, Al-Jen Rd., Sec. 1, Pau-An, Jen-Teh Hsiang, Tainan Hsien , Taiwan, R.O.C.
ABSTRACT
In this study, a rapid and simple method without a derivatization process for determination of the free sterols in vegetable and animal oils was developed. A direct injection gas chromatography with a non-polar megabore column (DB-1, 5 m x 0.53 mm, 1μm) was used. The recoveries of cholesterol, campesterol, stigmasterol and β-sitosterol from lard were at the range of 89%-106% with a coefficient of variation less than 12%. Total sterols were determined using the same method after saponification of the oil sample. Fourteen samples, including olive oil, sunflower oil, peanut oil, soybean oil, sesame oil, lard and egg yolk oil, were quantitatively analyzed for total and free sterols. The contents of total cholesterol, brassicasterol, campesterol, stigmasterol, β-sitosterol,Δ5-avenasterol,Δ7 -stigmastenol and Δ7-avenasterol in test samples were at the range of 193-34384, 0-1222, 0-2356, 0-1365, 0-5414, 0-608, 0-1296 and 0-129 μg/g, respectively; while the contents of free cholesterol, brassicasterol, campesterol, stigmasterol, β-sitosterol, Δ5-avenasterol, Δ7-stigmastenol and Δ7-avenasterol were 98-30340, 0-1057, 0-634, 0-724, 0-3087, 0-404, 0-558 and 0-23 μg/g, respectively. The amounts of esterified sterols were calculated by subtracting the free sterol contents from total sterol contents. Results showed olive oil, sunflower oil and peanut oil primarily contain esterified sterols; while soybean oil, sesame oil, lard and egg oil contain mostly free sterols. The developed method is recommended as a rapid method to determine if animal fats/oils are adulterated with vegetable oils.
Key words: total sterol, free sterol, esterified sterol, fats and oils, gas chromatography, direct injection.