SOYBEAN OIL PHOSPHOLIPIDS: IDENTIFICATION, QUANTITATION, AND EFFECT ON SOYBEAN OIL STABILITY

The phospholipids of crude and degummed oils were isolated and separated by column chromatography and thin layer chromatography. Standards and specific spray reagents were used to identify the phospholipids. Phospholipids identified in the crude and degummed oils were phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidic acid, lysophosphatidylcholine, lysophosphatidylethanolamine, and phosphatidylglycerol. Several unknown compounds were also present. Samples of crude and degummed oil were collected from four soybean oil processors over four consecutive days. Total and individual phospholipids were quantitated by determining the phosphorus content. The total phosphorus content varied between companies, with the average crude phosphorus content of the four sources ranging from 453 to 676 ppm. The average phosphorus content of the degummed oil of the four processors ranged from 12 to 84 ppm. These processors removed from 86 to 98% of the phosphorus present in the crude oil during the degumming process. There was also a daily variation in phosphorus removal within the individual companies. During the degumming process the proportion of phosphatidylcholine decreased and the proportion of unknown, nonpolar phosphorus compounds increased in samples from all companies. Higher levels of phosphatidic acid and lyso compounds were found in the degummed oil of some but not all companies. Accelerated stability tests showed that high levels of phosphorus could be correlated to a decreased level of peroxide formation. Crude oil had the slowest rate of peroxide formation, followed by degummed oil, and then refined oil. Lecithin added to refined soybean oil reacted in a similar manner. There did not appear to be a difference between the addition of equal amounts of nonhydratable phospholipids and hydratable phospholipids. When the major phospholipids were individually added to refined oil, phosphatidylethanolamine caused significantly lower peroxide formation than the other phospholipids. Phosphatidic acid caused greater peroxide formation than the other phospholipids and the refined oil without phospholipids