3 supercritical CO2 extraction methods for egg yolk lecithin
Egg yolk powder is rich in lecithin, but also contains more cholesterol and triglycerides that need to be removed. Therefore, how to extract high-purity and high-quality lecithin from egg yolk powder has become a research hotspot.
The methods of producing lecithin include organic solvent purification and supercritical CO2 extraction.
The pure organic solvent extraction process produces products with lower purity, higher cholesterol content, residual harmful organic solvents in the product, and the process is more complicated.
As a new type of separation technology, supercritical fluid extraction has the characteristics of simple process, high efficiency, low energy consumption, environmental protection, no solvent residues, and high selectivity. The lecithin produced is of high quality and is a high-purity egg yolk lecithin. Advanced technology.
Supercritical CO2 extraction is a very environmentally friendly extraction method.
Method for supercritical CO2 extraction of lecithin
The main components of egg yolk powder are egg yolk lecithin (about 17wt%), neutral lipids (also known as egg butter, the main components are triglycerides and cholesterol, >40wt%) and egg yolk protein (>40wt%).
Neutral lipids, especially cholesterol in them, are the enemies of cardiovascular and cerebrovascular and should be removed from lecithin products.
The content of lecithin, especially the content of phosphatidylcholine PC, is the main indicator to measure the quality of lecithin products.
Lecithin is more polar and usually insoluble in SC-CO2 (supercritical CO2 fluid, the same below), while neutral lipids have greater solubility in SC-CO2. In addition, both lecithin and neutral lipids are soluble in ethanol, while vitellin is insoluble. Based on these characteristics, the researchers proposed the use of supercritical CO2 extraction technology to prepare egg yolk lecithin. In summary, there are mainly the following three typical processes:
Plan A：Ethanol solvent extraction and supercritical CO2 fluid extraction method for lecithin
In the first step, the egg yolk powder is extracted with an organic solvent (ethanol) to obtain a liquid mixture of neutral lipids, lecithin and ethanol. The ethanol is removed by vacuum distillation to obtain egg yolk lipids containing phospholipids.
In the second step, SC-CO2 is used to remove the neutral lipids in the egg yolk lipids, and what is left is high-purity lecithin.
The advantage of the ethanol solvent extraction + supercritical CO2 extraction method is that high purity egg yolk lecithin without organic solvents and neutral lipids can be obtained, and it has superior oxidation stability.
The problem is that in the process of large-scale production, in the later stage of SC-CO2 extraction, when the phospholipid concentration in the extractor reaches a certain value, the viscosity of the extract may be too large, so that SC-CO2 cannot penetrate the material layer. , The mass transfer effect becomes worse.
Plan B： Supercritical CO2 extraction + supercritical CO2 and co-solvent ethanol method for lecithin
Step 1: Use supercritical CO2 to extract egg yolk powder to remove neutral lipids;
Step 2: Add a certain proportion of entrainer ethanol to supercritical CO2 for extraction, and the obtained product is distilled to remove ethanol to obtain high-purity egg yolk phospholipid.
The advantages of the method of supercritical CO2 extraction + supercritical CO2 and co-solvent ethanol extraction of egg yolk phospholipids are:
(1) The phospholipid product has high purity and no residual toxic organic solvents;
(2) There are few types of equipment required, and material conversion is relatively simple.
The disadvantages of the method of supercritical CO2 extraction + supercritical CO2 and cosolvent ethanol extraction of egg yolk phospholipids are:
(1) If the separation of carbon dioxide and ethanol is not complete in the second step, when carbon dioxide with ethanol circulates into egg yolk powder, a small amount of lecithin will be extracted by ethanol into neutral lipids, which will affect the yield of lecithin;
(2) In the later stage of the extraction process, the egg yolk powder may be battered and agglomerated, resulting in low extraction efficiency and low product yield.
Plan C： Supercritical CO2 extraction + ethanol solvent extraction method for lecithin
Step 1: Extraction with supercritical CO2 can remove the neutral lipids in the egg yolk powder.
Step 2: Solvent extraction method is used to extract high-purity egg yolk lecithin from egg yolk powder from which neutral lipids have been removed. Use edible ethanol with a concentration greater than 95% for suction filtration to obtain an extract containing lecithin. After the extract is distilled under reduced pressure or spray-dried, high-purity egg yolk phospholipids can be obtained.
The advantage of the method of supercritical CO2 extraction + ethanol solvent extraction of lecithin is that the whole process will not cause unnecessary loss of phospholipids
The problem to be solved is to improve the efficiency of removing neutral lipids in the first step.
Experimental study on the method of supercritical CO2 extraction of lecithin from egg yolk powder
The first step of plan B and plan C is to use supercritical CO2 extraction to remove neutral lipids from egg yolk powder.
After analysis, in order to solve the problem of incomplete extraction due to agglomeration in supercritical extraction, after improving the barrel of the key equipment extractor, the experiment of supercritical CO2 extraction and removal of egg yolk powder was carried out.
Aiming at the problem of agglomeration of egg yolk powder in the supercritical CO2 extraction process, we used a special material to layer the barrel.
Experimental results and discussion of the CO2 extraction method of lecithin
The effect of pressure on extraction rate
It can be seen from the experimental results that the higher the extraction pressure, the higher the removal rate of egg butter and the faster the extraction speed.
At 46 MPa, the removal rate can reach more than 95% in 2 to 3 hours. However, as the pressure increases, the requirements for equipment increase, the cost of production increases, and unsafe factors increase.
In the test under 32MPa and the test under 40MPa, the removal rate of egg butter is greater than 90%, which is a better process.
From the perspective of appropriately reducing the pressure, the extraction can be carried out at a pressure of 32-40 MPa.
We conducted a control experiment under the conditions of pressure 32MPa, temperature 60℃, 10 layers, and 3.5 h. The removal rate of egg butter reached 90.63%. If the extraction time is appropriately increased, the extraction rate will be higher.
The influence of the number of barrel layers on the removal rate
Because the egg yolk powder particles are very fine, the oil content is high, and the dense accumulation structure makes the permeability of the bed worse, if there is no layering, the egg yolk powder extraction process will cause local agglomeration due to the effect of pressure. Incomplete extraction affects the removal rate of egg butter.
In some experiments, it was found that there were some hard lumps of different sizes in the raffinate. After breaking it, it was found that the inside was still yellow (the completely extracted egg yolk powder was white), and the extraction effect was definitely not good.
The layered extraction of egg yolk powder can effectively reduce the agglomeration of egg yolk powder and improve the removal rate of egg butter.
Effect of extraction temperature
The effect of temperature on the extraction process is more complicated, and the coupling effect with pressure is relatively large.
On the one hand, as the temperature increases, the density of CO2 decreases, reducing the solubility of egg butter in it; on the other hand, as the temperature increases, the volatility of the solute increases, the diffusion coefficient increases, and the mass transfer process accelerates. , Is conducive to extraction.
In general, under a certain pressure, there is a corresponding temperature that makes the egg butter removal rate reach the highest under this pressure.
And the higher the pressure, the higher the corresponding optimal temperature.
Under relatively high pressure and corresponding temperature, the removal rate of egg butter is significantly faster than that under relatively low pressure and corresponding temperature.
For example, if it is extracted at 32 MPa for 5 hours at 60°C, the removal rate of egg butter reaches 96.71%.
The removal rate of egg butter reached 98.29% after 2 hours of extraction at 46 MPa and 65°C.
Choosing appropriate extraction conditions, extraction with SC-CO2 can completely remove triglycerides and cholesterol in egg yolk powder.
In the pressure range of 24-46 MPa, an orthogonal experiment was carried out, and it was pointed out that the better extraction conditions were 32-40 MPa, 4h, 60°C, 10 layers.
Within the range of experimental conditions, the higher the extraction pressure, the higher the removal rate of egg butter and the faster the extraction speed.
After the egg yolk powder is layered and charged, it can effectively reduce the agglomeration in the extraction process, improve the removal rate of egg butter, and provide good operating conditions for the next step of extracting egg yolk lecithin.