Green and efficient Supercritical Fluid extraction, especially supercritical CO2 extraction technology, has received widespread attention and application in the field of natural product extraction in recent years.
Supercritical CO2 extraction combines traditional distillation technology with organic solvent extraction to effectively separate, extract and purify extracts using supercritical CO2 fluids. The advantages are high extraction efficiency and no solvent, no residual toxicity, natural active ingredients, and heat-sensitive ingredients are not easily broken down, the natural characteristics of the extract can be maintained to the maximum extent and selective separation is achieved.
Supercritical CO2 extraction in the food industry
In the food industry, supercritical fluid extraction technology has two distinct development trends, namely the removal of harmful substances and the extraction of active ingredients.
The supercritical CO2 fluid extraction process can solve many defects of traditional extraction technology, such as the use of toxic organic solvents, high energy use, and low extraction yield, for the removal of harmful components (processing caffeine-free coffee), active ingredient extraction (extraction of plant essential oils), etc.
Traditional Method vs Supercritical CO2 Extraction Process
- Traditional extraction methods of natural products in the food industry generally have many shortcomings such as the heavy use of organic solvents in the production process, pollution of the environment, long processing time, complicated operating steps, low extraction rate, and low purity of the extract.
- Supercritical CO2 extraction process compared with traditional extraction processes has better extraction and separation capabilities and does not cause pollution to the environment: It has the advantages of safety, energy-saving, non-toxic, harmless, no residual solvent, reusable solvent, low operating temperature, strong selectivity, non-flammability, etc. It is more suitable for the separation and purification of physiologically active substances and natural products.
Three major applications of supercritical CO2 extraction technology in the food industry
Supercritical CO2 technology mass production of high-purity food raw materials and food additives has become an industrial demand.
Applications 1#: Animal and Vegetable Oils
Supercritical CO2 extraction technology has a good effect in extracting and separating oil. For example, for various essential oils such as fish oil, rice bran oil, sand ginger oil, etc., the extraction rate basically reaches 80%~90%.
- Fish oil: Fish oil is unstable and easy to decompose and oxidize. Therefore, the traditional method of extracting and refining fish oil will lead to high-temperature degradation of fish oil, oxidative rancidity, and residual organic solvents. Supercritical CO2 extraction technology extracts fish oil from fish meat products and can obtain 80%~90% oil. The content of effective nutrient components DHA and EPA is better than that of fish oil extracted by traditional methods, and there is no organic solvent and residue; due to the extraction It is specially sealed in CO2 gas to achieve a bactericidal effect and is not easy to be oxidized and rancid; the unique fishy smell of fish oil can be separated from the extract by using supercritical CO2 fractionation technology, so that the fish oil can remove the fishy smell; if it is combined with molecular distillation technology, it can remove of plasticizers.
- Millet rice bran oil: In the experiment, the oil yield of millet rice bran oil extracted by supercritical CO2 reached 9.98%, which is better than other extraction methods, and the mass fraction of linoleic acid exceeds 57%.
Applications 2#: Natural Coloring
Supercritical CO2 extraction technology is mainly embodied in the extraction and separation of various natural pigments in food, especially lycopene and β-carotene.
β-carotene has many important physiological functions and is a good coloring agent. At present, the organic solvent extraction method is usually used. Due to the problem of solvent residue, it is easy to cause a certain degree of hazard.
In some laboratory experiments, try to use the supercritical CO2 extraction method to extract β-carotene, and achieved good results. For example, using Rhodotorula viscous as raw material, under the optimal extraction conditions (extraction pressure 30 MPa, temperature 40 ℃, CO2 flow rate 20 kg/h, extraction time 90 min), the extraction rate is 0.83%. The results show that the extraction of β-carotene by supercritical CO2 fluid is feasible, but the extraction rate is low, and the influencing factors in the extraction process need to be further studied.
Supercritical CO2 technology for extracting capsanthin from red pepper has a good extraction effect and has been widely used in the market. For example, India imported some CO2 extraction production lines from China and relied on the CO2 extraction and fractionation provided by Shanghai Jiaotong University in China. Technology has made significant gains.
The supercritical CO2 extraction and fractionation process can obtain a higher yield and recovery rate, and the extracted capsanthin has the highest yield and color value. Compared with the organic solvent method, the yield of capsanthin obtained by this technology is high, and the color value of the product is high.
Applications 3#: Pesticide Residue Testing
Supercritical CO2 technology can be used to analyze food and detect food pesticide residues: this technology can become a sample pretreatment technology for the monitoring and analysis of trace pesticide residues in food, with high extraction efficiency, short time, relatively safe, environmentally friendly, and can avoid volatile pesticides loss and degradation.
Four Factors to Improve CO2 Extraction Efficiency
In the supercritical CO2 extraction process, the nature of the raw materials, ie relative molecular mass, polarity, etc., are internal factors affecting the extraction of supercritical fluids. In terms of the extraction yield and biological activity of the active ingredients, solvent selection, extraction pressure, and temperature, separation pressure and temperature, fluid flow rate, and extraction time are externally controllable factors, of which the pressure and temperature of the extraction are most obvious and can be optimized by experiment. The following four factors can improve the CO2 extraction rate:
Factors 1#: Raw material particle size and moisture content
Particle size: When the biomass is solid, the physical state of the sample has a large effect on the extraction effect. If the pulverization particle size affects the mass transfer rate and thus the extraction yield, it is necessary to select a suitable pulverization particle size to increase the surface contact area of the material and the solvent as much as possible.
Moisture Content: We recommend that the moisture content of biomass should be less than 10%. Usually, a certain amount of water in the biomass will also reduce the extraction yield, and the extraction yield of the selected dry biomass will be significantly improved.
Factors 2#: Temperature and Pressure
The pressure and temperature extracted during supercritical CO2 fluid extraction have a significant effect on the extraction.
- By increasing the extraction pressure, the density and solubility of the solvent can be increased, and the extraction yield can be increased.
- On the other hand, when the extraction pressure is constant, increasing the extraction temperature reduces the solvent density, but also promotes the mass transfer rate of the material.
Therefore, the optimum extraction pressure and temperature should be determined based on the extraction yield of the target compound.
Factors 3#: Co-solvent
Co-solvent, also known as a carrier or entrainer, can be mixed with a fluid solvent during supercritical fluid extraction, with volatility between the substance to be extracted and the supercritical component, which can improve solubility and selectivity.
However, the use of a co-solvent also has certain negative effects such as the residual problem of co-solvent in the extract. Therefore, the choice of co-solvent should take into account the nature of the Co-solvent, the nature of the extract, and the avoidance of harmful substances.
In the supercritical CO2 extraction process, CO2 low polarity limits the polar or lipophilic compounds to some extent. Changing the solubility of solute and the selectivity can in order to increase the application range of supercritical CO2 extraction: a co-solvent such as methanol, toluene, acetone, ethyl acetate, water, etc. may be added during the supercritical CO2 extraction process, generally not exceeding 5%, and the solubility of the extract in supercritical CO2 may be increased by more than 10 times.
Factors 4#: CO2 Flow
Therefore, selecting a reasonable CO2 flow rate can make the CO2 and the material have good contact and save resources.
The change in CO2 flow also has a certain influence on supercritical fluid extraction. When the CO2 flow rate increases, the residence time of the CO2 fluid in the extraction tank is short, which is not conducive to the increase of the extraction yield.
At the same time, the increase in CO2 flow will increase the mass transfer driving force in the extraction process, increase the mass transfer coefficient, and increase the extraction yield. When the CO2 flow rate exceeds a certain range, the CO2 dissolution capacity will drop sharply.