**2. The structure, composition and physical and chemical properties of soybean phospholipids**

Food Chemicals Codex (FCC) definites phospholipids as follows: Food grade phospholipids are complex mixtures obtained from soybean and other plants consisting of acetone insolubles (AIs) which are mainly phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI).

#### **2.1 Soybean phospholipids structure**

Phospholipids mainly include glycerol phosphatides and sphingomyelin. In this chapter, we mainly discuss glycerol phosphatides. The structures of phospholipids are shown in Fig. 1.

#### **2.2 Soybean phospholipids composition**

Phospholipids constitute 0.3%-0.6% of soybean seed, or 1.5%-3.0% of crude soybean oil. The phospholipids composition is shown in Table 1. The fatty acid composition of soybean phospholipids is shown in Table 2.

Soybean Phospholipids 485

Myristic(C14:0) 0.3-1.9 - - Palmitic(C16:0) 11.7-18.9 2.5-26.7 42.7 Palmitoleic(C16:1) 7.0-8.6 - - Stearic(C18:0) 3.7-4.3 9.3-11.7 - Oleic(C18:1) 6.8-9.8 17.0-25.1 39.4 Linoleic(C18:2) 17.1-20.0 37.0-40.0 55.0-60.8 Linolenic(C18:3) 1.6 4.0-6.2 9.2 Arachidic(C20:0) 1.4-2.3 - -

Soybean phospholipids are by-products of soybean oil refining process. Phospholipids composition can be affected by the oil refining processes and may decrease after frost. The lipase may contribute to phospholipids decrease during storage. Other minor compositions in soybean phospholipids include water, pigment, galactosyl glyceride, glycolipids,

Pure phospholipid is a white solid at room temperature, odorless and colorless. The color of phospholipid may be from light yellow to brown due to refining methods, product categories and storage conditions etc. Non decolored, once decolored and twice decolored are three grades of phospholipid color which is determined by Gardner colorimeter (AOCS

Soybean phospholipids are soluble in aliphatic hydrocarbons, aromatic hydrocarbons and halogenated hydrocarbons solvents, such as ether, benzene, chloroform and petroleum ether etc., and particularly soluble in aliphatic alcohol, for example ethanol. As other non-polar surfactants, soybean phospholipid is insoluble in polar solvent, for example methyl acetate, especially acetone (solubility less than 0.03g/L at 5 degrees Celsius). Phospholipids solubility in methyl acetate and acetone increases when there is a small amount of oil in the phospholipids. PC is soluble in ethanol while PI not. The soluble and insoluble portions of PE in ethanol are about equivalent. The differences of soybean phospholipids solubilities in the above solvents may provide references for isolation, purification and quantification of phospholipids. Soybean phospholipids are soluble in animal fat and vegetable oil, mineral

The hydrophilic phosphate group and alkaline and hydrophobic hydrocarbon keys in phospholipids molecules help to form a interface between water and oil which lowers the interfacial tension between water and oil and makes them stable colloidal. Soybean phospholipids exist in oil and have obvious hydrophilic colloid property. When mixed with suitable amount of water, phospholipids are isolated from oil. Particularly, in hot alkalescent water (pH>8) the phospholipids are more likely to absorb water and expand and then the colloidal solution is formed. Due to the above property, phospholipids are obtained

oil and fatty acids, but insoluble in cold animal fat and vegetable oil actually.

Low Intermediate High

Fatty acid Range(%)

Table 2. Fatty Acid Composition of Soybean Phospholipids (Szuhaj, 1989)

official method Td-La-64). The chromaticities are from 9 to 17.

from crude oil and are widely applied (Lu, 2004).

carbohydrates, sterols and tocopherol etc.

**2.3 Physical and chemical properties** 

**2.3.1 Physical properties** 

Fig. 1. Structures of phospholipids; A: Glycerol phosphatides structure; B: Sphingomyelin; R1, R2, R: Hydrocarbon chains; Point 'X' is likely composed of structures noted in the box.


Table 1. Composition of Soybean Phospholipids (Szuhaj, 1989)

Fig. 1. Structures of phospholipids; A: Glycerol phosphatides structure; B: Sphingomyelin; R1, R2, R: Hydrocarbon chains; Point 'X' is likely composed of structures noted in the box.

Phosphatidylcholine PC 12.0-21.0 29.0-39.0 41.0-46.0 Phosphatidylethanolamine PE 8.0-9.5 20.0-26.3 31.0-34.0 Phosphatidylinositol PI 1.7-7.0 13.0-17.5 19.0-21.0 Phosphatidic acid PA 0.2-1.5 5.0-9.0 14.0 Phosphatidylserine PS 0.2 5.9-6.3 - Lysophosphatidylcholine LPC 1.5 8.5 - Lysophosphatidylinositol LPI 0.4-1.8 - - Lysophosphatidylserine LPS 1.0 - - Lysophosphatidic acid LPA 1.0 - - Phytoglycolipids - 14.3-15.4 29.6

Low Intermediate High

Component Abbreviation Range(%)

Table 1. Composition of Soybean Phospholipids (Szuhaj, 1989)


Table 2. Fatty Acid Composition of Soybean Phospholipids (Szuhaj, 1989)

Soybean phospholipids are by-products of soybean oil refining process. Phospholipids composition can be affected by the oil refining processes and may decrease after frost. The lipase may contribute to phospholipids decrease during storage. Other minor compositions in soybean phospholipids include water, pigment, galactosyl glyceride, glycolipids, carbohydrates, sterols and tocopherol etc.

#### **2.3 Physical and chemical properties**

#### **2.3.1 Physical properties**

Pure phospholipid is a white solid at room temperature, odorless and colorless. The color of phospholipid may be from light yellow to brown due to refining methods, product categories and storage conditions etc. Non decolored, once decolored and twice decolored are three grades of phospholipid color which is determined by Gardner colorimeter (AOCS official method Td-La-64). The chromaticities are from 9 to 17.

Soybean phospholipids are soluble in aliphatic hydrocarbons, aromatic hydrocarbons and halogenated hydrocarbons solvents, such as ether, benzene, chloroform and petroleum ether etc., and particularly soluble in aliphatic alcohol, for example ethanol. As other non-polar surfactants, soybean phospholipid is insoluble in polar solvent, for example methyl acetate, especially acetone (solubility less than 0.03g/L at 5 degrees Celsius). Phospholipids solubility in methyl acetate and acetone increases when there is a small amount of oil in the phospholipids. PC is soluble in ethanol while PI not. The soluble and insoluble portions of PE in ethanol are about equivalent. The differences of soybean phospholipids solubilities in the above solvents may provide references for isolation, purification and quantification of phospholipids. Soybean phospholipids are soluble in animal fat and vegetable oil, mineral oil and fatty acids, but insoluble in cold animal fat and vegetable oil actually.

The hydrophilic phosphate group and alkaline and hydrophobic hydrocarbon keys in phospholipids molecules help to form a interface between water and oil which lowers the interfacial tension between water and oil and makes them stable colloidal. Soybean phospholipids exist in oil and have obvious hydrophilic colloid property. When mixed with suitable amount of water, phospholipids are isolated from oil. Particularly, in hot alkalescent water (pH>8) the phospholipids are more likely to absorb water and expand and then the colloidal solution is formed. Due to the above property, phospholipids are obtained from crude oil and are widely applied (Lu, 2004).

Soybean Phospholipids 487

The processing steps are as follows: The crude oil is heated to 80 degrees Celsius and then centrifuged and passed through the flowmeter followed by addition of 80 degrees Celsius

Degumming oil and oil foot sediments are produced and they can be separated by centrifugation. The hydrated oil foot should be concentrated immediately to avoid microbial rancidity due to the high moisture and neutral oil content. Oil foot (or mixed with hydrogen peroxide or fluidity agent in advance) is pumped into the agitated film dryer. Phospholipids film is formed under gravity or centrifugal force and the pressure of incoming production materials and flow to the bottom of the vessel while moisture evaporates under high temperature and vacuum conditions. The motionless fluid product is dried at vacuum (726 mm Hg) and 100-110 degrees Celsius for 2 min and then cooled to obtain concentrated soybean phospholipids with less than 1% moisture content. The concentrating procedure should be operated under vacuum as phospholipids are thermosensitive (Ji & Li, 2005).

Mechanically pressing crude soybean oil is preheated to 80 degrees Celsius after removal of

The amount of water added is determined by phospholipids content in the oil and the changes of phospholipids granules formed during heating and is normally 3.5 times (w/w) the content of phospholipids. The water added is usually boiling or 0.7% hot salt solution is used. The speed of adding water is determined by the water absorption velocity of phospholipids. The faster the latter the faster the former, and vice versa. When adding water, the stirring speed must be fast and is normally 80-100rpm at the beginning and is slowed down 20-30min later when large flocculent phospholipids granules are formed and the stirring is continued for another 20-30min. Then the liquid is left standing still to settle. The supernatant of the upper phase is dehydrated to produce refined oil while the oil foot of

The hydrated phospholipids oil foot is drawn into the concentrating tank by vacuum and subjected to temperature rising and stirring. Vacuum dehydration of phospholipids occurs at about 80 degrees Celsius. When there is slight silk flash while stirring the fluidic phospholipids the moisture content is consistent with the specification. The moisture content is about 5%. Phospholipids after concentration is a brown semisolid and can be used

Decoloration of concentrated phospholipids is needed for preparation of high quality phospholipids. The amount of 30% hydrogen peroxide added to the concentrating tank is 2%-2.5% (w/w) of the concentrated phospholipids. The phospholipids are decolored in the closed tank for 1h at 50 degrees Celsius without vacuum. Then turn on the vacuum pump and heat the mixture to 70 degrees Celsius. Dehydrate until there is no water in the water

the lower phase need to be concentrated to obtain phospholipids products.

knock vessel. The decolored phospholipids are light brown.

**3.1.1 Continuous processing** 

water of 2% (w/w) of the oil.

**3.1.2 Batch processing** 

impurities by filtration.

3.1.2.1 Preheating

3.1.2.2 Hydration

3.1.2.3 Concentration

3.1.2.4 Decoloration

in food, medicine and industry.

Phospholipids consist of fluidic and plastic phospholipids. Fluidic phospholipids have the flow property of Newtonian fluid and the fluidity of plastic phospholipids increases with the addition of fatty acids. The viscosity of phospholipids is affected by such factors as AI (acetone insoluble) content, moisture, mineral content, acid value (AV) and various additives for example plant-based surfactant. Generally, high AI or water content results in high viscosity while high AV results in low viscosity. Some bivalent minerals for example Ca2+ affect viscosity too.

N-hexane insolubles (HIs) make fluidic phospholipids turbid. The turbidness not only influence the appearance of the products, but also leads to precipitation in long-term storage. The phospholipids also get turbid when the water content is over 1% (Wu, 2001).
