Abstract
Soybean lecithin is known to be less stable at 60°C or elevated temperatures and susceptible to discoloration upon heating for a long period of time, but its major phospholipids remain unchanged at temperatures up to 100°C, with minor components undergoing discoloration as reported previously. As an accelerated thermal-deterioration test, soybean lecithin was refluxed in octane (bp 125.7°C), and then, its thermally deteriorated or decomposed products exhibiting the UV absorption maxima at wavelengths of 350 nm, 280 nm and 240 nm were yielded, respectively. The thermally deteriorated product exhibiting the UV absorption maximum at a wavelength of 350 nm was separated, purified and studied, leading to the finding that the four, heretofore unknown compounds were chemically and structurally identified as a thermally deterioration substance derived from phosphatidylethanolamine. The thermally deteriorated product of soybean lecithin yielded after refluxing in octane for 9 hrs was deffated with acetone and extracted with methanol, and the extract was treated with hexane, washed with 60% aq. ethanol and extracted with 90% aq. methanol. The extract was chromatographed on a silica gel column (elution with a 2:3 mixture of methanol:chloroform), and the isolated four compounds were subjected to acidic methanolysis, followed by chromatographic analysis to determine the fatty acid compositions and spectral analysis by use of IR. 1H-NMR, 13C-NMR and MS to conduct the structural identifications. The identified four compounds were all found to contain phosphatidylethnolamine intact, except that the terminal amino group is involved in the formation of [4,2,0]-diazabicyclic structure.
