Oxygenated fatty acid constituents of soybean phosphatidylcholines

Bitter‐tasting phosphatidylcholines from hexane‐defatted soybean flakes were chromatographically separable from ordinary soy phosphatidylcholines (SPC). The bitter‐tasting SPC contain 32% oxygenated fatty acids in addition to palmitic, stearic, oleic, linoleic, and linolenic acids. Identification of these oxygenated acids was based on infrared, ultraviolet, proton nuclear magnetic resonance, and mass spectral characteristics of methyl ester derivatives which were separated and purified by column and thin layer chromatography. The fatty acid methyl esters identified were (a) 15, 16‐epoxy‐9, 12‐octadecadienoate, (b) 12, 13‐epoxy‐9‐octadecenoate, both with double bonds and epoxide groups predominantly of cis configuration; (c) 13‐oxo‐9,11‐and 9‐oxo‐10, 12‐octadecadienoates; (d) 13‐hydroxy‐9, 11‐ and 9‐hydroxy‐10, 12‐octadecadienoates; (e) 9, 10, 13‐trihydroxy‐11‐ and 9,12,13‐trihydroxy‐10‐octadecenoates. In addition, trace amounts of (f) 11‐hydroxy‐9,10‐epoxy‐12‐and 11‐hydroxy‐12,13‐epoxy‐9‐octadecenoates; (g) 13‐oxo‐9‐hydroxy‐10‐and 9‐oxo‐13‐hydroxy‐11‐octadecenoates; (h) 9,10‐dihydroxy‐12‐ and 12, 13‐dihydroxy‐9‐octadecenoates; and (i) 9,12,13‐dihydroxyethoxy‐10‐ and 9,10,13‐dihydroxyethoxy‐11‐octadecenoates were indicated by mass spectrometry. Dihydroxyethoxy compounds (i) were possibly formed upon extraction of the SPC from flakes by 80% ethanol. Except for the first two epoxy compounds, labelled a and b, the oxygenated fatty acids are similar to the products formed by homolytic decomposition of linoleic acid hydroperoxide. The first two compounds with predominantly cis configuration may occur by action of fatty acid hydroperoxides on an unsaturated fatty acid.