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.
Therefore, 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 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.
We will to mainly introduces 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.
Supercritical fluid extraction technology is a new type of extraction and separation technology which 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.
The emergence of supercritical 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.
Basic principle of supercritical fluid extraction
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.
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.
Supercritical fluid extraction experiments began in the 19th century, especially in recent years, which have gradually replaced traditional solvent-based extraction techniques. Hannay and Hogarth first discovered that supercritical fluids have a unique dissolution phenomenon.
In 1869 Thomas gave the concept of “critical point”. These early studies provided the direction for the development of supercritical fluid extraction technology.
Supercritical fluid extraction technology is the process of extracting a mixture by utilizing the good permeability and solubility characteristics of the fluid.
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.
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.
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.
There are many types of supercritical solvents, and different solvents have different critical properties.
Divided by non-polar solvents and polar solvents, mainly carbon dioxide, ethylene, propylene, ethane, propane and methanol, ethanol, ammonia, water and so on.
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 temperature due to its lower critical pressure (7.38 MPa) and lower critical temperature (31.1 °C).
Nitric oxide (36.5 ° C), ethane (32.4 ° C), propane (96.8 ° C) methanol (240.5 ° C) are not conducive to separation due to the high critical temperature, and the CO2 critical density (0.47 g / cm3) is higher than the commonly used super The critical solvent is high, so it has strong ability to dissolve organic substances, does not cause damage to heat sensitive substances and active ingredients, is safe and non-toxic, has no solvent residue problem, and has anti-oxidation sterilization effect, which is beneficial to ensure and improve the quality of natural products.
It is widely used in the excellent extraction of food flavors, vegetable oils and alkaloids, and in various fields such as medicine and cosmetics.
Factors influencing supercritical fluid extraction
In the supercritical 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.
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 a 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)
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.
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.
Use of entrainer
Entrainer, also known as a carrier, can be mixed with a fluid solvent during supercritical fluid extraction, with a 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.
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.
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 of 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.
Therefore, selecting a reasonable CO2 flow rate can make the CO2 and the material have good contact and save resources.
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.
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.
Removal of harmful substances
Supercritical fluid extraction can selectively remove harmful substances from food. The most widely used is the production of caffeine-free coffee. West Germany HAG began using caffeine to remove caffeine in 1978.
At present, the technology can be used not only in coffee but also in tea, Chinese medicine such as partner grass. In the process of extracting tea leaves and companion grass, a suitable pressure combined with a temperature of about 60 ° C can increase the extraction yield.
Supercritical fluid extraction can also extract hops for brewing beer, which removes harmful components such as hard resins and pesticides, and maintains the aroma of hops.
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.
Choi studied the extraction of fluoroquinolone antibiotics (enoxacin, danofloxacin) in pork using supercritical fluid extraction using Na4EDTA and sea sand combined with 80 ° C, 30 MPa CO 2 and 30% methanol. And ciprofloxacin) effect is significant.
There are also some harmful substances mainly from pesticide residues and environmental pollution. Valverde studied the residual pesticides in rice, wild rice and wheat by supercritical extraction technology at an extraction pressure of 20 MPa, extraction temperature. 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 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 technology has great The advantage is that the content of deacidified oil, 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 oxyglycerols from shark liver oil.
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.
Wu Lianzeng et al. proposed a patented technology for extracting seabuckthorn oil by supercritical carbon dioxide technology.
Liu Junhai also studied rice bran oil and found that the extraction rate of supercritical carbon dioxide is between 19.2% and 20.4%, and the color and purity of oil are relatively relative. better.
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.
Aromatic plants, fruits, beans and seeds are the main sources of natural antioxidant compounds.
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.
Yuhui et al. obtained the peony essential oil by supercritical CO2 extraction. Compared with the traditional steam distillation extraction and organic solvent extraction, the floral fragrance is rich, the yield is up to 0.6% and the volatile substances are more, the main fragrance is 1,3. , 5-trimethoxybenzene, octane, and the like.
Problems and directions
As a new, clean and efficient green extraction and separation method, supercritical fluid extraction technology has been widely concerned and widely used.
Because of its high concentration of concentrated extracts and solvent-free residues, it is not only in the food industry, but also in pharmaceuticals.