ISOLATION AND QUANTITATIVE-DETERMINATION OF STEROL OXIDES IN PLANT-BASED FOODS - SOYBEAN OIL AND WHEAT-FLOUR

Soybean oil and wheat flour were analyzed for the content of sitosterol oxides. The method involved chromatography on a Lipidex-5000 column and enrichment on a disposable NH2-column, yielding a sterol fraction and a sterol oxide fraction. Each fraction was separated as trimethylsilyl-ethers on a methyl silicone capillary column. Analysis of crude and freshly refined soybean oil showed no detectable levels of the isomeric 5,6-epoxysitosterols, the epimeric 7-hydroxysitosterols and 5,6-dihydroxysitosterol at the detection limit of 0.2 ppm. Storage of a refined soybean oil for one year at 4-degrees-C caused no significant increase in the level of free sitosterol oxides when compared to the freshly refined soybean oil. Analysis of three wheat flours (at 2, 8 and 36 months) revealed that the samples contained variable levels of 5-alpha,6-alpha-epoxysitosterol (5.4-55 ppm in the lipids), 5-beta,6-beta-epoxysitosterol (0.2-29 ppm), 7-alpha-hydroxysitosterol (9.3-118 ppm) and 7-beta-hydroxysitosterol (9.7-126 ppm).