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Supercritical CO2 Extraction Of Natural Zeaxanthin


Zeaxanthin is mainly composed of lutein, zeaxanthin and cryptoxanthin and other carotenoids. It is a kind of natural pigment widely existed in many plants and is also a kind of compound necessary for the human body.

Supercritical CO2 extraction of zeaxanthin
Supercritical CO2 extraction of zeaxanthin

Natural food coloring

Zeaxanthin is a natural food coloring agent, it is not only a natural pigment, but also the production of health food additives, they as natural pigments have been in Europe and the United States and other countries approved for food pigments, in the corn kernel contains about 0. 01~0. 9mg/100g. Because of the uncertainty about the potential impact of synthetic pigments and related additives, such natural food additives are widely welcomed today.

Medicinal effect

In recent years, the research on the function of zeaxanthin has drawn more and more interest.
It mainly focuses on the relationship between zeaxanthin and ophthalmopathy, heart disease and cancer. At the same time, their antioxidative properties are of great interest.
Epidemiological studies have shown that the intake of vegetables rich in carotenoids (including zeaxanthin) is negatively correlated with the occurrence of cancer.
Ingesting foods rich in carotenoids can improve health and reduce the risk of developing cancer, cardiovascular, Department of disease and cataract risk.

Supercritical CO2 extraction

The results show that the use of supercritical CO2 extraction technology in the extraction of Zeaxanthin can get high yield, high color price, non-toxic zeaxanthin products, and provide an effective way for comprehensive utilization of corn industry.

Supercritical extraction experiment of zeaxanthin

In the supercritical CO2 extraction experiment, the extraction temperature, pressure, time, and cosolvent are the main factors that affect the extraction effect.

Since the critical temperature of CO2 is Tc=31.1℃ and the critical pressure Pc=7.38MPa, the extraction temperature range is 35~45℃, the pressure range is 17-23MPa, and the extraction time range is 120~180min.

Taking zeaxanthin extraction rate and purity as indicators, and on the basis of single factor experiment, using four factors of extraction temperature, extraction pressure, extraction time, and cosolvent as variables, a four-factor three-level orthogonal test was performed to determine the super A better combination of critical CO2 extraction of zeaxanthin.

Comparative study with solvent method

The solvent extraction method is continuous extraction with absolute ethanol (analytical purity) in a Soxhlet extractor at 60℃ for 24 hours, and supercritical CO2 is continuous extraction for 3 hours. Compare its purity and extraction rate.

Condition optimization of SFE

The effects of cosolvents

The effect of four different cosolvents of methanol, absolute ethanol, acetone and n-hexane with the same amount of 20% methanol on the extraction was investigated under the conditions of temperature 40℃ and pressure 30MPa unchanged.

Methanol has the best effect, followed by anhydrous ethanol, and acetone and n-hexane are inferior.

Taking into account the edibility of the pigment, we choose absolute ethanol as the cosolvent.

Experiments show that when no cosolvent is added, zeaxanthin can hardly be obtained; as the amount of anhydrous ethanol increases, the yield of zeaxanthin increases; when the content of anhydrous ethanol is 20%, its yield The highest rate, continue to increase the amount of absolute ethanol, due to the increase in the amount of impurities extracted, the yield of zeaxanthin has declined.

The influence of operating pressure on extraction yield

At a certain extraction temperature, when the pressure increases, the extraction yield increases, especially when the pressure increases from 20 MPa to 30 MPa, the extraction yield increases a lot; but the pressure increases from 30 MPa to 40 MPa, the extraction yield increases very little, indicating that the solvent dissolves Ability and pressure are not directly proportional to the linear relationship. Considering equipment investment, the operating pressure is selected to be 20~35MPa.

The influence of operating temperature on extraction yield

The relationship between temperature and extraction yield is more complicated.

In different pressure ranges, temperature has diametrically opposite effects on solubility, which is actually caused by the different effects of temperature on solvent density and solute volatility (vapor pressure).

When the pressure is higher, the density of the solvent CO2 is higher and the compressibility is lower. The CO2 density of the solvent is not reduced by the temperature rise, but the vapor pressure of the solute increases significantly, so the concentration of carotene in the supercritical CO2 phase increases; When the pressure is low, the increase in solute volatilization caused by heating is not enough to compensate for the decrease in solvent CO2 solubility, and the overall effect leads to a decrease in the carotene content in the supercritical CO2 phase.

It can be foreseen that for a certain system, there must be a pressure. When extracting under this pressure, the temperature has little effect on the solute concentration. This pressure is called Critical Extraction Pressure, or CEP for short.

The analysis of the experimental comparison results shows that when the pressure is low, it is more advantageous to operate at a low temperature, and when the temperature is higher, it is advantageous to extract at a higher pressure.

For the extraction of zeaxanthin, the operating pressure is 30-35MPa, and the operating temperature is 20-40℃.

Influence of extraction method and extraction time

SFE extraction can have three methods: static, dynamic and combination of static and dynamic.

Experiments show that: the extraction rate of a single static 1 hour is only 37% of the combined extraction rate of static 20min and dynamic 30min; and under the same conditions, the extraction rate of a single dynamic 1h is 73% of the combined extraction rate of dynamic 45min and static 15min, and The dynamic extraction rate basically reaches equilibrium within 2h, so it is better to adopt static extraction for 20min and then dynamic extraction for 2h.

The influence of CO2 flow rate on extraction yield

The CO2 flow rate has a certain effect on the extraction yield. When the CO2 flow rate is small, the extraction rate of carotene is smaller and the operation time is longer; as the CO2 flow rate increases, the extraction yield rate increases. After reaching a certain amount, the increase rate of extraction yield becomes slower. Therefore, the flow rate of solvent CO2 is selected at 20~25kg/h.

Gas consumption ratio

How much fluid is needed per unit mass of raw material (that is, gas consumption ratio), so that the extraction effect can be guaranteed without wasting CO2, which is an important parameter in production.

We tested the influence of a series of gas consumption ratios under the fixed conditions of pressure of 20MPa, temperature of 40℃, and anhydrous ethanol content of 20%. The experiment showed that the best gas to material ratio was 40:1.

The optimal extraction conditions for extracting zeaxanthin with supercritical CO2 are:

The extraction temperature is 40℃, the extraction pressure is 23MPa, the extraction time is 180min, and the cosolvent is 10% of absolute ethanol.

Compared with solvent method

The solvent extraction method uses a chemical solvent (anhydrous ethanol, analytically pure) in a Soxhlet extractor at 60°C for 24h continuous extraction, while supercritical CO2 is continuously extracted for 3h.

The results show that the supercritical CO2 extract has no solvent residue and good color. The extraction time is only 1/8 of the solvent method, and the extract yield is 9.8%, which is 2.2% higher than the 7.6% yield of the solvent extraction method.

Product stability

The zeaxanthin was placed indoors under normal temperature and natural light (but no direct sunlight) for 1 month. The content of zeaxanthin was measured and found to lose about half, and it was almost completely decomposed after 2 months of storage.

For example, under dark conditions: it will be all lost when stored at room temperature (about 20-26℃) for 5 months, and it will only lose nearly 60% when stored at 0℃ for 6 months; when stored at -15℃ for more than 6 months, The loss is only 30%; it can be seen that the product needs to be stored at low temperature and protected from light.

in conclusion

The process conditions for supercritical CO2 extraction of natural pigments containing zeaxanthin from corn gluten meal are studied:

That is, 23MPa, 40°C, 30% absolute ethanol as the cosolvent, and the extraction time is 3h.

The yield of supercritical C&extract is 2.2% higher than that of solvent extraction.

The stability of the product has been investigated, and it is recommended that the product be stored at low temperature and protected from light.

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