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Supercritical CO2 fractionation reduces lard cholesterol

Forewords

Supercritical fluid fractionation (SFF)

Supercritical fluid fractionation (SFF) is a separation technology that has been developed rapidly recently. It has the characteristics of achieving solute separation at a lower temperature, and is particularly suitable for separating unstable and hardly volatile substances.

In general, when supercritical fluid is used as a solvent, its solvent capacity mainly depends on the density. When the pressure is increased at a constant temperature, the density of the supercritical fluid increases, and the solvent capacity increases; when the temperature is increased at a constant pressure, its solvent capacity Ability is weakened.

Since the temperature of the fractionation section is set to rise from bottom to top, a certain temperature difference is formed. Therefore, under the condition of constant pressure, when the supercritical fluid phase flows upward through the fractionation section, the dissolving power will decrease due to the increase in temperature, which will cause part of the content to be contained. The solute liquid separates out, flows back to the packing layer to form an internal reflux, exchanges mass and energy with the rising extraction phase, to achieve the purpose of liquid phase extraction or fractionation.

Lard and Cholesterol

Lard contains a large amount of saturated fatty acids, oleic acid and linoleic acid and other unsaturated fatty acids. It has a higher melting point and is resistant to frying, and has the characteristics of good flavor, good taste, high stability and less oily smoke. Only lard contains high The amount of cholesterol (approximately 100mg/100g) is more worrying about use.

How to reduce the cholesterol in lard and make lard become a healthy and nutritious fat that is widely accepted by consumers is the main focus of this research project.

Supercritical CO2 extraction (SFE)

Supercritical carbon dioxide fluid extraction (SFE) has high selectivity for solutes and low operating temperature, which can avoid thermal damage and no solvent residues. In addition, carbon dioxide has the advantages of safety, non-toxicity, non-reactivity and easy complete separation from the solute, so Quite a lot of attention by scholars and industry.

Since the 1980s, many researchers have applied supercritical carbon dioxide extraction technology to reduce cholesterol in foods. Among them, the extraction of cholesterol in fats is the most researched, and butter is the most commonly studied in fats.

It was used to extract cholesterol and fat in egg yolk and egg powder. In addition, it is also used in the extraction of cholesterol in fish oil, squid oil, tallow, lard, fish, beef, etc.

Distillation technology

Generally, traditional distillation technology uses the difference in relative volatility between substances to achieve the purpose of separation. When the relative volatility is less than 1.1, it is not economical to use traditional distillation technology to separate at this time.

For systems with azeotropes, they cannot even be separated. At this time, special distillation techniques such as azeotropic distillation, extractive distillation, salt-added distillation, pressure-sensitive distillation, and reactive distillation are needed to achieve the purpose of purification.

Distillation technology

Generally, traditional distillation technology uses the difference in relative volatility between substances to achieve the purpose of separation. When the relative volatility is less than 1.1, it is not economical to use traditional distillation technology to separate at this time.

For systems with azeotropes, they cannot even be separated. At this time, special distillation techniques such as azeotropic distillation, extractive distillation, salt-added distillation, pressure-sensitive distillation, and reactive distillation are needed to achieve the purpose of purification.

Principles of Supercritical Fluid Fractionation

The liquid feed of supercritical fluid fractionation enters from the upper or middle section of the fractionation tower, and after reverse contact with the supercritical carbon dioxide entering from the bottom of the tower, the difference in the solubility of the separated matter in carbon dioxide is used to make the separated distillate and residue The materials flow out from the top and bottom of the tower.

Characteristics of supercritical fluid fractionation

In addition, for the distillation and purification of alcohols, the use of supercritical carbon dioxide can destroy the azeotropic situation. After solving the traditional distillation, the azeotrope still needs to be purified by molecular sieves. Traditional distillation is likely to cause damage to the active substances in biotech products due to high temperature operation. Fractionation through supercritical carbon dioxide is low in operating temperature and the product can be recovered as long as the pressure is reduced. This not only avoids the destruction of the effective ingredients, but also at the same time. Reach the goal of energy saving and carbon reduction.

In addition to the component separation of the activity of the crude extract obtained from the extraction to achieve the purpose of “concentration and purification”, if the separation is azeotropic, it cannot be separated by traditional distillation, such as the separation of water and IPA, which can also be easily achieved with this technology.

SFF temperature

In the near supercritical region, the temperature is very sensitive to the influence of supercritical carbon dioxide fluid, so the correct selection of the temperature of the fractionation section is extremely important for the quality of the separation result. The temperature of the fractionation section can be determined by experiment to ensure normal operation. Generally, when the temperature is 10-40°C higher than the critical temperature, the normal operation of the system can be ensured and a good separation effect can be obtained.

Temperature difference in fractionation section

Because the reflux of the supercritical fluid fractionation packing section increases the temperature along the packing column at a certain pressure, reduces the solvent capacity, and makes the fractions with less solubility separate from the supercritical fluid phase, so the temperature difference in the fractionation section directly affects The size of the backflow and the larger temperature difference are beneficial to improve the separation efficiency.

Research method

  • After purchasing commercial lard, perform a GC test to detect the content of cholesterol, saturated fatty acids and unsaturated fatty acids, so as to understand the health quality and indicators of commercial lard;
  • Carry out Taguchi experiment design and analysis, and carry out supercritical carbon dioxide fractionation experiment test according to the design method;
  • At the same time, the optimized experimental design will verify the best operating conditions obtained by the Taguchi experimental design method, and conduct the supercritical carbon dioxide fractionation experiment under the optimal parameters;
  • The cholesterol-lowering lard obtained after the experiment will be used to detect cholesterol again by GC to evaluate the efficiency of cholesterol removal.

Carry out pig fat dry-refining lard under optimal operation prediction parameters, carry out supercritical carbon dioxide fractionation experiment, and perform GC test before and after the experiment to detect cholesterol content, evaluate cholesterol removal efficiency and oil health and safety.

Execute job flow

  • The lard is first filtered through a filter bag to remove suspended and solid impurities.
  • Fill the lard into a 4L raw material storage tank, and perform a return flow to remove the air in the pipe.
  • Adjust the fractionation conditions to be tested according to Taguchi design parameters, including: pressure, temperature, CO2 flow, solution flow and other control factors that affect the supercritical fractionation experiment.
  • After setting the pressure and temperature of the first/second separation tank, the pressure of the fractionation tower was increased to the working pressure to carry out the supercritical fractionation experiment of lard.
  • Collect fractions from each separation tank every 15 minutes, and observe and record the changes in the collection amount and fractionation time of each separation tank, and compare whether there are obvious differences between the separation tank fractions (such as: the intensity of the odor, the color The depth, the amount of collection, etc.), until the raw materials are completely fed, continue to collect until the separation tank can not collect the fractionated liquid.
  • Perform GC-MS and other detection and experimental data and result analysis

Research content

Taguchi quality engineering was developed and advocated by Dr. Taguchi Genichi in the 1950s. Using simple orthogonal table experimental design and concise analysis of variance, with a small amount of experimental data for analysis, effectively improve product quality.

So it was quickly popularized in the Japanese industry, and it was called Quality Engineering (Quality Engineering).

The biggest feature of Taguchi method is to obtain useful information with fewer experiments. Although it is not as good as the full factor method to find the exact optimal position, it can point out the optimization trend with a few experiments.

Conclusion and suggestion

In this project, Taguchi experimental design method combined with ANOVA analysis can be used to know the optimization condition trend of cholesterol fractionation experiment from the optimization prediction of the two.

Test results

The fresh lard was not fractionated and the cholesterol was 1262.86ppm before it was made. Taguchi and ANOVA analyzed the lowest cholesterol concentration after fractionation to optimize the experimental value of 290ppm, which is partly different from the experimental verification data of optimized conditions of 173.7ppm.

We can also find that there is also a slight gap between the actual verification group value and the optimized predicted value. It should be the less influential factor C (temperature on the fractionation tower) and factor D (mass flow rate) among the experimental factors. Compared with), the results caused by these two factors are slightly different. There is a certain difference between the predicted value and the actual value itself. Based on the analysis results of this experiment, such a value can be trusted.

Therefore, the combination of optimized conditions for the cholesterol fractionation experiment calculated by various experimental analysis tools is meaningful and trustworthy in the experimental design method. In this study, the fresh lard was subjected to supercritical carbon dioxide. After fractionation

In conclusion

Cholesterol content can be reduced from 1262.86ppm to a minimum of 173.7ppm, which can reduce the cholesterol content by 86.25%, reaching the goal of greatly reducing the cholesterol content in lard. In this research experiment, the raw lard only undergoes a supercritical fractionation process It can achieve the effect of greatly reducing cholesterol. In the future, there will be further reflux fractionation tests. It is expected that the cholesterol content can be reduced to less than 50ppm, which is more in line with the needs of modern healthy diet.