Soybean minor constituents phospholipids

Oil recovered by solvent extraction or mechanical pressing is termed crude soybean oil and contains various classes of lipids. It consists primarily of neutral lipids, which include tri-, di- and monoacylglycerols, free fatty acids, and polar lipids such as phospholipids. It also contains a minor amount of unsaponifiable matter that includes phytosterols, tocopherols, and hydrocarbons such as squalene. Trace metals are found in soybean oil in ppm concentration. When the oil is refined, concentrations of all minor constituents are reduced. The typical composition of crude and refined soybean oil is shown in Table 2.2. 

Phospholipids can be obtained from various sources, two of which are oilseed lecithins and egg yolk lecithins. The phospholipid composition of soybean lecithin appears to vary according to the method of extraction. PC content ranges from 29 to 46% PE, from 21 to 34% and PI, from 13 to 21%. Other minor constituents are phosphatidylserine, phosphatidic acid, lyso-PC, lyso-PE, and lyso-PI. In addition to soybeans, lecithin has been found in many other oilseeds, including peanuts, cottonseed, sesame, safflower, and sunflower, among others. 

Phospholipids (Figure 3) are constituents of membranes and are only minor components of oils and fats, sometimes responsible for cloudiness. They are usually removed during degumming, the residue from soybean oil processing being a source of phospholipids used as food emulsifiers. The term lecithin is used very loosely for such material, and it may variously mean phosphatidylcholine, mixed glycerophospholipids, or cmde phospholipid extracts from various sources. Where possible, more specific nomenclature or the source and purity should be used (14). 

Standard-grade, commercial lecithin from the soybean is a complex mixture. It comprises phospholipids, triglycerides, and minor amounts of other constituents (i.e., phytoglycolipids, phytosterols, tocopherols, and fatty acids). The composition and molecular arrangement of this heterogeneous mixture of compounds defines a product that is low in apparent polarity and has a strong tendency to promote water-in-oil (w/o)-type emulsions (31). 

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