Dry distillation
dry distillation is the most traditional method of extracting egg oil in my country, and it is still in use. “Rihuazi Materia Medica” says: “(Egg) yolk, stir-fry to get oil and powder.” Leave the egg yolks, heat them in a copper pot over low heat, and then use high heat after the water evaporates, and then boil out Egg Yolk Oil”. Now it is clinically used to treat burns or sores and is still extracted by dry distillation. Boil 20-40 fresh eggs, mash the egg yolks, stir-fry in an iron pan until the oil turns black, then turn off the heat and let it stand, filter it with sterile gauze. This method has a very low oil yield, is difficult to carry out industrialized production, and the oil has poor color and luster and smell, and the phospholipid content is low, which may contain the carcinogen benzopyrene. Therefore, it is generally only used for a small amount of clinical use, not as a method of mass extraction.
Baking method
Grind the boiled egg yolk and put it in an oven, dry it with air at 60 ℃ for 8-10 hours, put it in a preheated high-temperature resistant container and heat it to 100 ℃ with low heat, then adjust it to a strong fire, Continue to heat under airtight conditions until the egg yolk becomes viscous and an oily liquid precipitates out. Pour out the liquid and let it cool to get ready. The oil yield of this method is 26.95%, the oil yield is also low, and contains a lot of impurities, the process is not standardized, the quality is difficult to control, and the color and smell are poor.
Vacuum distillation method
take the boiled egg yolk, grind it and dry it with air at 60°C for 6 hours, put it into a three-neck bottle, and distill it in an electric heating mantle to a sand bath temperature of 250°C at atmospheric pressure, and start to yolk at 100°C Under reduced pressure, distill under reduced pressure at a pressure of 0.05-0.06 MPa and an egg yolk vapor temperature of 280±5°C for 4 h. The oil yield of this method reaches 55.89%, and it is decolorized and deodorized, and has the effect of synergizing efficiency and reducing toxicity.
Solvent extraction method
The solvent method is commonly used to extract egg oil in industry. The oil in egg yolk is extracted by using the property of egg oil insoluble in water but soluble in organic solvents such as ethanol, ether, and chloroform, that is, oil extraction. Chop the boiled egg yolk, put it in a Soxhlet extractor, heat and reflux the egg yolk with chloroform at 60°C in a water bath to extract until the egg yolk turns white, and recover the chloroform to obtain an orange-red oily liquid. The average yield was 35%, of which the fatty oil content was 88.9%. Eggs less than 7 days old were taken out, centrifuged to obtain yolk, and dried at 30-50°C. With the extraction ratio of dry egg yolk: ethanol = 1:4, extract at 30-50 °C for 1-2 hours, vacuum filter, and distill under reduced pressure to obtain egg oil.
Enzymatic extraction
take egg yolk powder and add water to make egg yolk liquid 20 g/d L, adjust the pH and temperature appropriately, add protease A at a ratio of 100:1 for hydrolysis for 2 h, then add protease B at a ratio of 100:1.5 for hydrolysis 2 h, inactivate the enzyme at 90 °C for 30 min, and then centrifuge at 4 000 r/min for 15 min to obtain the egg oil in the upper layer. This method has an oil yield of 58.89%, does not contain phospholipids, but has a high fatty acid content. Fresh eggs are separated by beating eggs to obtain egg yolk, add deionized water, adjust the pH and temperature to the optimum value of enzyme action, add protease A and B at 1.5 g/100 g for hydrolysis, and hydrolyze for 2 and 3 hours respectively. Decompose the egg yolk liquid, adjust the pH to 5, heat and insulate at 90 ℃ for demulsification, and centrifuge at 4 000 r/min for 15 min. Get the upper layer of fluid egg oil I (triglyceride), the second layer of gelatinous egg oil II (rich in phospholipids), etc. The extraction rate of total phospholipids reaches 89.86%, and the triglyceride and phospholipids are separated well, and the content of lecithin in the jelly part reaches 37.09%. This method can simplify the extraction process, reduce pollution and increase the extraction rate.
Subcritical propane extraction
Put the egg yolk powder raw material into the extraction kettle, heat the propane to 50-70 ℃, and then flow upward through the raw material bed from the bottom of the extraction kettle to extract the egg yolk, and then depressurize to propane through the pressure control valve of the saturated vapor pressure, combine the propane with the egg oil in a separator. The egg oil obtained contained 79.8% triglyceride, 15.0% cholesterol, 1.1% lecithin and 4.1% cephalin. The method is simple in operation, low in extraction pressure, recyclable propane, low in solvent consumption, and high in extraction efficiency. However, propane is flammable and explosive, and certain safety measures need to be taken. The extracted Egg Yolk Oil not only has low phospholipid content, but also contains protein, which needs to be dissolved and removed with chloroform-methanol mixture.
Supercritical CO2 extraction method
Put the egg yolk powder into the extraction cylinder, heat or cool the extraction cylinder, separator I, and separator II to make the temperature reach 55 ℃, open the CO2 purity cylinder, the CO2 flow rate is 10 kg/h, and adjust the extraction The pressure was 30 MPa, and the extraction was performed for 4 h. The extraction rate reached 81.26%, and gas chromatography analysis showed that the total unsaturated fatty acid content reached 67.25%. Through the orthogonal test, it was found that the factors affecting the extraction rate of egg oil from the largest to the smallest were extraction pressure, CO2 flow rate, and extraction temperature. Take the egg yolk powder dried for 4 h in a vacuum oven at 50 °C and a vacuum degree of 0.9 MPa, and perform supercritical CO2 extraction. The extraction pressure is 32 MPa, the extraction temperature is 49 °C, and the extraction is performed for 5 h. The extraction rate of Egg Yolk Oil is 97.52%. .
Others
enzymatic hydrolysis-solvent extraction method: use fresh egg yolk as raw material, add water to prepare egg yolk liquid, add protease to hydrolyze, centrifuge, extract with ethanol, and then perform desolvent treatment to obtain Egg Yolk Oil rich in phospholipids. This method has a high total oil yield, and the protein oil is divided into two parts: neutral fat and phospholipid-rich.