FOOD SCIENCES PURIFICATION OF EGG YOLK OIL OBTAINED BY SOLVENT EXTRACTION FROM LIQUID EGG YOLK Aleksandrs Kovalcuks Latvia University of Agriculture [email protected] Abstract There are different methods of egg yolk oil extraction, but still solvent extraction is commonly used. Due to the high cost of egg yolk powder production, extraction of lipids from liquid egg yolk remains very topical. Crude egg yolk oil obtained by solvent extraction from liquid egg yolk contains high amount of water which can decrease shelf life of egg oil promoting lipid oxidation. High concentration of residual solvents limits the usage of egg oil in food or in cosmetics due to the health risks. The aim of this study is to purify egg yolk oil obtained by solvent extraction from liquid egg yolk. Results show that it is possible to decrease the water content in egg oil from 14.26 ± 1.29% to 0.88 ± 0.13% by eliminating lecithin from egg oil. Solvent evaporation in the rotary film evaporator under the vacuum cannot remove solvents completely from the extract, but nitrogen streaming through the extract as a last step in evaporation process removes solvent residues, leaving behind high quality egg yolk oil suitable for food application. Key words: egg yolk oil, solvent extraction, purification. Introduction possible changes of its highly valuable compound Egg yolk oil is a good source of unsaturated content. fatty acids, oil soluble vitamins, phospholipids and 2-propanol is a polar solvent and it is miscible with cholesterol, and it can be widely used as an ingredient water forming a hydrogen-bonded structure (Tabata et in food and cosmetics, but extraction of lipids from al., 1994). But it is also quite non-polar, because of egg yolks is a complicated process. First of all, the its hydrophobic alkyl group, what makes it soluble in structure of egg yolk does not allow using standard non-polar solvents such as hexane. This can be one lipid extraction methods like pressing. Egg yolk of the reasons for high water content in oil micelle lipids are associated with proteins, which makes lipid before solvent evaporation. 2-propanol high solubility extraction process even more complicated (Ahn et in water makes extraction of this compound from al., 2006). There is a method which requires protein aqueous phase into a non-polar solvent very difficult degradation by the heat, but egg yolk proteins are a (Tabata et al., 1994). 2-propanol extraction to the very valuable product to be discarded such way. That hexane can be promoted by process called ‘salting is why solvent extraction of egg yolk lipids is the most out’ where inorganic salt, usually sodium chloride, justified method. Solvent extraction of egg lipids can is dissolved in water to reduce solubility of the be applied on egg yolk powder and liquid egg yolk. 2-propanol in water phase (Hasseine et al., 2009). Production of egg powder is an expensive process 2-propanol, due to its polar nature, will extract which requires high amount of energy. For that reason, polar phospholipids (lecithin) from the egg yolk. the extraction of liquid egg yolks is studied as a most Lecithin is a good emulsifier and it can form very stable economically reasonable method. Usage of organic emulsions (Maximiano et al., 2008). Lecithin binds solvents has some benefits in egg oil production such water presented in liquid egg yolk by the swelling. as antimicrobial effect that allows using liquid egg In vegetable oil refining this process is used for wet yolk for extraction without heat treatment reducing degumming. Wet lecithin can contain up to 50% of production costs. But the usage of organic solvents is water and its drying is a big challenge. Wet lecithin related to the health risks; therefore, solvent presence in egg yolk oil can be another reason for high water in final product must be prohibited. content in crude egg yolk oil because lecithin drying In previous studies 2-propanol/hexane solvent in the rotary evaporator is not so efficient (Palacios mixture was chosen as the best solution for extraction and Wang, 2005a). So, one of the possibilities for of egg lipids from liquid egg yolk. Lipids in egg yolk decreasing water content in egg yolk oil is lecithin are presented as polar phospholipids and non-polar or elimination during the extraction process. neutral lipids. 2-propanol denatures egg yolk proteins For the separate phospholipid extraction more and extracts polar lipids. Hexane, as a non-polar polar solvent is needed. In this case ethanol can be solvent, extracts neutral lipids (Christie, 1993). But the best choice. Ethanol is more polar than 2-propanol egg yolk oil extracted that way contains high amount and it will also denature yolk proteins. But in this of water which can decrease oil quality during the time extraction must be done in two stages. First, storage promoting lipid oxidation. liquid egg yolk needs to be extracted with ethanol to The aim of this study was to purify egg yolk oil eliminate polar phospholipids and then neutral lipids obtained by the solvent extraction and determine will be extracted from precipitates with hexane. The 142 RESEARCH FOR RURAL DEVELOPMENT 2014, VOLUME 1 PURIFICATION OF EGG YOLK OIL OBTAINED BY SOLVENT EXTRACTION FROM LIQUID EGG YOLK Aleksandrs Kovalcuks big difference between ethanol and hexane polarities by volume at ratio 30:70 and poured into a beaker. causes phase separation in two layers when they Liquid homogenized egg yolk was added to solvent are mixed together. Increasing of reaction surface mixture with a thin squirt vigorously mixing. The can improve extraction between two phases, but ratio 2:1 between solvent mixture and egg yolk was it needs to be aware of vigorous mixing to avoid used. Extraction was done at temperature of 20 °C emulsion formation. After phase separation all polar vigorously mixing for 30 minutes. Extracts were compounds, like phospholipids, salts, sugars and filtered using vacuum filtration, collected in to a clean soluble proteins will take place in polar ethanol-water container and then transferred to a separatory funnel. phase, but neutral lipids will be diluted in non-polar hexane phase which must be free from water (Palacios Salting out 2-propanol from the egg yolk lipid extract and Wang, 2005a). Egg yolk oil can be obtained from For salting out of 2-propanol saturated sodium this non-polar phase by the evaporation of the hexane. chloride water solution (26 g 100 ml-1) was added to Volatile organic solvents can be removed from the extract at dosage 10 ml for 100 ml of extract and lipid extracts in rotary evaporators. For decreasing the well mixed. After mixing, extract was left for 1 hour evaporation temperature this process usually occurs for phase separation. Then bottom aqueous layer was under the vacuum. But this process is not sufficient for drained by the opening in a stopcock of separatory total removal of solvents from the extracts. Increasing funnel. the evaporation temperature can cause unwanted The oil was recovered by evaporation of the changes in lipids. Pure and dry nitrogen is commonly solvent mixture using rotary evaporator IKA RV 10 used in laboratories for solvent evaporation from the Control (IKA-Werke GmbH & Co. KG) at 80 °C and extracts. Nitrogen is inert gas and in comparison with 400 m bar pressure. air it does not contain oxygen, which can react with lipids. Two stage lipid extraction with ethanol and hexane The combination of rotary vacuum evaporation Lipid extraction with ethanol and hexane from and nitrogen blowing through the extract may have liquid egg yolk was made by following steps. First, a good result for the total solvent removal. Nitrogen lecithin was extracted with ethanol from liquid egg yolk bubbles going through egg oil will sufficiently increase and then neutral lipids were extracted from precipitate evaporation surface and pick up solvent vapors from with hexane (Schreiner, 2006). For lecithin extraction, the product. The same process conditions of rotary 200 g of homogenized liquid egg yolk was added to evaporation, such as temperature and vacuum, will 400 ml of ethanol and stirred until egg yolk proteins intensify solvent and nitrogen removal from egg oil. denatured and completely dispersed. Extraction was Nitrogen will also remove air from the oil that will done at 20 °C for 30 minutes. Then, the mixture was decrease oxidation of lipids by the air oxygen. filtered by vacuum filtration, and the supernatant This method can also be used for large scale was collected and transferred to a separatory funnel. solvent removal using industrial nitrogen generators, The precipitate was extracted with 400 ml hexane which produce pure and dry nitrogen. vigorously mixing for a 30 minutes at 20 °C using a magnet stirrer. Extract was filtered by vacuum Materials and Methods filtration and supernatant was collected and added to Materials the same separatory funnel. Both ethanol and hexane Hen eggs from Lohman Brown Classic breed extracts were thoroughly but gently, to avoid emulsion were provided by JSC Balticovo (Iecava area, formation, mixed to extract polar lipids and impurities Latvia). Egg yolks were separated from egg whites to a polar ethanol-water phase and neutral lipids to a and homogenized. Moisture content of homogenized non-polar hexane phase. Then the mixed extracts were egg yolks were determined using Moisture balance left for 1 hour for phase separation. Bottom ethanol/ MOC-120H (Shimadzu, Japan) at 120 °C until weight water layer, containing polar lipids and water soluble difference from the previous weighting was less than compounds such as salts, sugars, soluble proteins, 0.05%. was drained from separatory funnel through the open All solvents (ethanol, hexane, 2-propanol) used stopcock and collected in a clean container.