Egg yolk lecithin fractionation and characterization

Egg-yolk lecithin has a unique composition and potential applications. The purposes of this research were to study the effects of yolk oil and yolk protein denaturation on phospholipid (PL) extraction or fractionation with ethanol, and to develop an efficient method for the fractionation of large amount of egg-yolk lecithin from fresh yolk and evaluate its functional properties. To achieve the first objective, fractionation was performed with deoiled and undeoiled yolk and with heated and unheated yolk. The recovery of total PLs in the PC-enriched fraction and the remaining PL fraction was higher (70%) from the undeoiled than from the deoiled yolk (60%). However, protein denaturation only had slight effect on PL extraction. Better enrichment of PC was observed by extraction from undeoiled than from the deoiled yolk. Cholesterol content of the PC-enriched fraction obtained from the undeoiled yolk was much higher than that from the deooiled yolk. To achieve the second objective, ethanol was used to dehydrate and partially extract PLs, followed by hexane to extract the total lipids. An acetone precipitation of PLs from the final polar lipid fraction was necessary to remove residual neutral lipids, especially cholesterol. PL purity of the final product was about 95.5%. Surface tension reduction, emulsion stability and oxidative stability studies were conducted to characterize egg-yolk lecithin\u27s functional properties. Compared with soybean lecithin, egg-yolk lecithin had similar surface activity as evaluated by surface tension reduction in an aqueous system and critical micelle concentration (CMC). Soyben lecithin created a more stable emulsion than did egg-yolk lecithin. However, egg-yolk lecithin was more oxidatively stable than soybean lecithin