When eggs containing foods are fried several times, with same frying oil, such small foams are seen in the frying oil that are hardly vanish away after the foods have been teken out. This foaming is assumed to be due to the phosphatides in egg yolk. The purpose of this study is to investigate the effect of each phosphatide to the foam-forming of frying oils.
Soybean phosphatides were fractionated by mainly column chromatography into phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS) etc. Oils containing each phosphatide being heated at 160°C, a chip of potato was dipped in the oil for 30 s, and the amount and duration of forming were measured. Acid value, surface tension, viscosity, and color of the oils were mesured after measurement of the foaming of the oils was over.
The results showed that there were large variations in the foam-forming properties of each phosphatide. The foam-forming properties of PC was weaker than those of PE and PS. The development of red color during heating of oils containing PE and PS was remarkable. Each phosphatide did not have an effect on such physical properties of the oils as surface tension and viscosity except the changes in color.