PREFERENTIAL DEGRADATION OF NONCHOLINE PHOSPHATIDES IN SOYBEAN LECITHIN BY THERMALIZATION

Purified soybean lecithin and the gum derived from soybean oil process ing were heated separately in bulk at 125 to 200 degrees C for 60 min, or at 175 degrees C for 30, 60, 90 and 120 min, and the products were analyzed by thin layer chromatography and high performance liquid chr omatography. It was found that the noncholine phosphatides are prefere ntially degraded relative to phosphatidylcholine, and that these phosp hatides are broken down in the order phosphatidylethanolamine (PE) > p hosphatidylinositol (PI) > phosphatidic acid (PA) with increasing temp erature. At 175 degrees C, the heating time required to degrade the no ncholine phosphatides was between 30 and 60 min. Diglycerides were the principal products of thermalization at 77% of the total material, in dicating that the 3 phosphoester linkage is the most heat-labile porti on of the noncholine phosphatide molecules. Cleavage of the fatty acid s from positions 1 and 2 of the phosphatides was minimal, as indicated by the relatively low amount of free fatty acids (8% of the total) wh en the lecithin was heated at 180 degrees C for 90 min. The appearance of brown discoloration, characteristic of heated lecithin, coincided mainly with the decomposition of PE.