Egg‐yolk lipid fractionation and lecithin characterization

Abstract

Egg-yolk lecithin has phospholipid (PL) classes and a FA composition that differ from soybean lecithin and may have unique functional properties. The purposes of this research were to develop an effective method for extracting a sufficient amount of lecithin from fresh egg yolks and to evaluate its functional properties. Ethanol was used to dehydrate and partially extract the PL, after which hexane was used to extract the total lipids. A phase separation of the combined extracts resulted in neutral and polar lipid fractions. An acetone precipitation of PL from the final polar lipid fraction was necessary to remove the residual neutral lipids, especially cholesterol. The purity of PL in the lecithin product was 95%. Surface tension reduction, emulsion stability, and oxidative stability studies were conducted to characterize the functional properties of egg-yolk lecithin. Egg-yolk lecithin and soy lecithin had similar surface activities, as evaluated by the surface tension reduction in an aqueous system and the critical micelle concentration. Soybean lecithin created a more stable emulsion than egg-yolk lecithin. However, egg-yolk lecithin was more oxidatively stable than soybean lecithin.Paper no. J11030 in JAOCS 82, 571-578 (August 2005). KEY WORDS:Egg-yolk lecithin, emulsion stability, functionality, phospholipids, oxidative stability, surface tension.Egg yolks are a good source of phospholipids (PL). PL represent approximately 10% of the wet weight of the egg yolk (1), equivalent to about 22% of the total egg yolk solids. The main components of egg-yolk lecithin are PC (80.5%) and PE (11.7%). Egg-yolk lecithin also contains lysophosphatidylcholine, sphingomyelin, and neutral lipids in minor quantities. The extraction of the total lipids or the PL from yolks is desirable because of the unique properties and valuable applications of these products (2). Yolk lecithin is used in the pharmaceutical and cosmetic industries as an emulsifier, and it is not as commonly used in foods as soy lecithin, because of its commercial availability and unfamiliar functional properties. It was recently reported that dietary egg-yolk PC can significantly lower cholesterol absorption in rats compared with soybean PC (3). In addition, egg-yolk lecithin contains relatively more saturated FA than does soybean lecithin, and it may have better oxidative stability than soybean lecithin. Therefore, yolk lecithin may have certain unique applications in foods. According to the limited information available in the literature, egg-yolk lecithin is primarily extracted with solvents such as diethyl ether, hexane, chloroform, and ethanol. However, some of these solvents are considered undesirable because of environmental and health concerns (2,4). Earlier research focused mainly on total lipid extraction and cholesterol removal. Sequential extractions with various solvents or a multisolvent system were investigated (5,6). Other PL fractionation techniques, such as ethanol extraction and then low-temperature crystallization to remove the solidified...

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