Supercritical CO2 extraction process in the food industry

Food industry and supercritical CO2 extraction

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. 

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.

Why choose supercritical co2 extraction

Supercritical fluid extraction technology has attracted extensive attention as a new and green extraction process. Compared with traditional extraction processes, it has better extraction and separation capabilities and does not cause pollution to the environment.

Supercritical CO2 extraction technology 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. Therefore, it has become an effective means of separating products in the food field.

The subject of this article

We will mainly introduce the basic principle of supercritical fluid extraction, the important variables affecting the extraction process, and how to optimize it. Focuses on the application of supercritical fluid extraction technology in the food industry, such as extracting active ingredients from plants, animals, and agricultural by-products.
Solve the problems of organic solvent residues in the traditional extraction process, provide new methods for the preparation and extraction of samples in the test, provide new technical means for small and medium-sized industrial production, and provide theoretical basis and technical support for the development of new products.

What is the supercritical CO2 fluid extraction process?

Supercritical fluid extraction technology is a new type of extraction and separation technology that has been developed rapidly and widely used in recent years. It utilizes the high density and low viscosity of its fluid to selectively extract effective from natural substances. Ingredients, effectively improve and improve the quality of the product. At present, with the pursuit of “green food” and “natural products”, traditional extraction and separation technologies can no longer meet the requirements of high-purity and high-quality products.

What is a supercritical CO2 extraction used for?

The emergence of supercritical CO2 fluid extraction technology can solve many defects of traditional extraction technology, such as the use of toxic organic solvents, high energy use, and low extraction yield. Moreover, since most of the nutrients in foods such as vitamins and proteins are prone to decomposition, polymerization, oxidation, and other metamorphic reactions, the destruction of active ingredients and environmental pollution may occur during the use of conventional extraction techniques. At present, supercritical fluid extraction technology has been widely used in food, medicine, biology, and other aspects.
In the food industry, there are hundreds of domestic and foreign supercritical fluid extraction technologies for the removal of harmful components (processing caffeine-free coffee), Active ingredient extraction (extraction of plant essential oils), etc., has obvious effects and has been put into industrial production. Supercritical fluid extraction technology has opened up a wide range of applications for the food industry.

Work principle of supercritical fluid extraction

The mobile phase is subjected to pressure and temperature to make the extract Some components are dissolved and carried by the supercritical fluid so that the substances to be separated are selectively extracted according to the solubility capacity, the boiling point, and the molecular weight, thereby selectively extracting the active ingredients or removing the harmful substances. 

Supercritical fluid means that when the substance exceeds its own critical temperature and critical pressure, the gas-liquid two phases will mix into a uniform fluid state. The fluid has both high gas permeability and liquid-like high solubility. The fluid density is controlled by changing the pressure and temperature, thereby controlling the solubility of the supercritical fluid, and the supercritical fluid is sufficiently contacted with the substance to be separated to form a mobile phase.

Advantages

Supercritical fluid extraction (SFE) combines traditional distillation technology with organic solvent extraction to effectively separate, extract and purify substrates and extracts using supercritical 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, and the natural characteristics of the extract can be maintained to the maximum extent and selective separation is achieved.

Application of supercritical CO2 extraction

The CO2 extraction process is widely used in the excellent extraction of food flavors, vegetable oils, and alkaloids, and in various fields such as medicine and cosmetics.

The density and dielectric constant of a supercritical fluid are proportional to the pressure, and by increasing the pressure, molecules of different polarities can be gradually extracted. However, because it is greatly affected by temperature and pressure, the extracted flavor component is less reproducible, so it is not suitable for quantitative analysis of flavor components in food.

CO2 is the most commonly used supercritical fluid. It has the most research, the widest application, and abundant sources. It can be separated at lower temperatures due to its lower critical pressure (7.38 MPa) and lower critical temperature (31.1 °C).

The CO2 extraction process for the food industry

In the supercritical CO2 fluid 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.

Adjusting the following key extraction process factors can improve the extraction rate:

Raw materials

The raw materials are solute, the sample to be extracted, and the supercritical fluid extraction is suitable for solid or liquid samples. The extraction process of different samples is also slightly different.

When the sample 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.

Usually, a certain amount of water in the sample will also reduce the extraction yield, and the extraction yield of the selected dry sample will be significantly improved.

Solubility (temperature and pressure)

For natural and complex samples, it is necessary to test and analyze a number of different influencing factors and effects and optimize the extraction process parameters by response surface analysis or orthogonal test.

The pressure and temperature extracted during supercritical 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.

Co-solvent

However, the use of entrainer also has certain negative effects such as the residual problem of entrainer in the extract. Therefore, the choice of entrainer should take into account the nature of the entrainer, the nature of the extract, and the avoidance of harmful substances.

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. When supercritical fluid extraction uses a single gas, solubility and selectivity are often limited to some extent.

If the most widely used fluid is CO2, its low polarity limits the polar or lipophilic compounds to some extent. In order to increase its potential application range, change the solubility of solute and the selectivity of supercritical fluid. An entrainer 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.

CO2 flow

Therefore, selecting a reasonable CO2 flow rate can make the CO2 and the material have good contact and save resources.

The change of 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.

Application of 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.

In the food industry, supercritical fluid extraction has the outstanding feature of the traditional extraction process technology, that is, on the basis of the residue without residue, the deactivation deformation of the heat-sensitive substance can be prevented. The first application to industrial production was the removal of caffeine from coffee beans using supercritical fluid extraction. So far, nearly 100 foods have been systematically extracted and separated, and many products have been introduced to the market, such as ginger essential oil, caffeine-free coffee, and wheat germ oil.

Removal of harmful substances

Some health-friendly or harmful substances such as polycyclic aromatic hydrocarbons, polychlorinated biphenyls, veterinary drugs, etc., which are present in foods, can also be extracted by supercritical fluid extraction techniques.

There are also some harmful substances mainly from pesticide residues and environmental pollution. At 50 °C, CO2 combined with methanol as an entrainer can successfully extract pesticide residues, and the effect is much better than the traditional use of ethyl acetate as an extraction solvent.

There may also be several toxins in the food such as mycotoxins, algal toxins, or phytotoxins. In many cases, these toxins are mostly highly polar compounds, and Acorus calamus and Podophyllum hexandrum rizhomes have been found that compared to tradition. The Soxhlet extraction method makes it easier to successfully remove the isolated toxin using supercritical fluid extraction technology.

Some substances in some foods are non-toxic but reduce the overall quality of the food. For example, in the presence of free fatty acids in olive oil, soybean oil, grapefruit oil, etc., the extract can be deacidified by countercurrent supercritical fluid extraction.

Compared with the traditional chemical extraction process, this CO2 extraction process has a great advantage in that the content of deacidified oil, a free fatty acid in the raffinate, and the content of volatile compounds in the separator can be obtained. There are also some volatile compounds extracted from inactive dry yeast. A similar method is also used for the separation of essential oils, the recovery of essential oils, the extraction of natural vitamin E from wheat germs in agricultural by-products, and the extraction of polyglycerols from shark liver oil.

Extraction

The most widely used supercritical fluid extraction technique is the extraction of functional ingredients from plants. Plants such as wheat germ contain a large amount of linoleic acid, natural vitamin E, protein, etc., and eight essential amino acids can be extracted by supercritical fluid. Especially in the past decade, there have been many studies and reports on the extraction of biologically active substances such as antioxidant activity using supercritical fluids.

Another important application of supercritical fluid extraction is the extraction of essential oils from herbs. Essential oils are traditionally used in the manufacture of foods, cosmetics, cleaning products, perfumes, herbicides, and pesticides. Essential oils contain tens or hundreds of complex components, especially hydrocarbons (terpenes, sesquiterpenes) and oxygenates (alcohols, aldehydes, ketones, acids, phenolic compounds, oxides, Lactones, acetals, ethers, and esters have biological activities such as antibacterial and antioxidation in addition to the characteristic flavor.