Food industry and supercritical CO2 extraction
WHY CHOOSE SUPERCRITICAL CO2 EXTRACTION
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.
Subject of this article
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
What is it?
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.
What is a supercritical fluid used for?
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.
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Basic principle of supercritical fluid extraction
Features of supercritical CO2 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 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.
Application of supercritical CO2 extraction
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).
It is widely used in the excellent extraction of food flavors, vegetable oils and alkaloids, and in various fields such as medicine and cosmetics.
CO2 extraction process for food industry
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.
Adjusting the following key extraction process factors can improve the extraction rate：
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.
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.
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. 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.