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Application Progress of Supercritical Fluid Extraction in Tea Processing

     A supercritical fluid is a fluid whose temperature and pressure are above the critical temperature and critical pressure. This fluid combines the advantages of both liquid and gas, with a density of hundreds of times the gas close to the liquid, fluidity and viscosity close to the liquid, the diffusion coefficient is about one hundredth of the gas, hundreds of times larger than the liquid, Thus the supercritical fluid has a strong ability to dissolve, high extraction speed and better mass transfer performance, especially changes in temperature and pressure will lead to great changes in the density of the supercritical fluid, which can be considerably changed in the solute Of the solubility, by changing the physical parameters (temperature, pressure) method can easily improve the fluid solubility, so as to achieve selective extraction and separation purposes. CO2 is the most commonly used working medium for supercritical fluid extraction. The supercritical CO2 extraction process can be carried out at room temperature, and CO2 is non-toxic and has no residue. Therefore, it is especially suitable for the separation and purification of unstable natural products and active substances.


     Nearly 30 years, the supercritical fluid extraction technology in the food industry has developed very rapidly, such as some developed countries have the technology for hops extraction and coffee decaffeination and other industrial production, in addition, removed from the tobacco Nicotine, the extraction of high-grade natural flavors and pigments and flavor substances from plants, extraction of polyunsaturated fatty acids from fish oil and other aspects of research and application have made great strides. The technology in tea research and application has also attracted people's attention. Such as the removal of caffeine from tea, black tea extraction of aromatic substances.


1, remove the caffeine in tea

     Tea is rich in caffeine, accounting for about 2% to 5% of dry matter. Caffeine is an alkaloid that has a wide range of effects on the human body's metabolism. Some are beneficial and some are not very desirable. Excess consumption of coffee Some people eat very little caffeine and can not stand it because they can affect their health. To suit the needs of special populations, but also because the number of people who desire a healthy lifestyle as a whole is on the rise, the decaffeination approach has drawn considerable attention. As early as the 1950s, de-caffeinated black tea appeared. At first, the organic solvent method was used. This method can change the color, smell, taste and shape of the tea leaves, especially the residual organic solvents inevitably. With the deepening research and application of supercritical fluid extraction technology, people turn to the use of supercritical CO2 extraction technology to produce decaffeinated black tea.


2, extract aromatic substances from tea

     Tea has a unique aroma and flavor, its aromatic and flavor composition is very complex, most of these components are unstable substances, vulnerable to thermal deterioration or volatilization, so the operating temperature is very low supercritical CO2 extraction method is particularly superior.

     Vitzthum (1975) first conducted research in this area, extracting black tea with supercritical CO2 and separating the volatile components therein, and successfully identified 56 kinds of black tea aroma components in the volatile components separated and enriched by Porapak Q, Extraction pressure is 10 ~ 30Mpa, the separation pressure is 5 ~ 7Mpa; In addition, from the early 1980s, the former Federal Republic of Germany on the use of supercritical CO2 extracted from the black tea aromatic substances as food additives, the extraction process conditions temperature 40 ℃, pressure 30Mpa, time 4h.


3, extracted from the tea pigment

     In recent years, the extraction of pigment from tea carried out more research, are generally used organic solvent method, this method can get the crude pigment mixture, but the solvent consumption, low efficiency, high cost. The author (1996) carried out extraction of green tea with supercritical CO2 extraction of green pigment, the choice of a suitable entrainer can significantly improve the yield of green pigment.


4, extracted from the tea polyphenols

     Tea polyphenols is a component of tea that has an important physiological activity on the human body. It has high medicinal value and strong anti-oxidation ability and has been widely valued by people. In recent years, the development and utilization of tea polyphenols products become the focus of deep processing of tea. Now the production of tea polyphenols extracted from tea are organic solvent method. Li Jun et al. (1996) attempted to study the extraction of tea polyphenols from supercritical CO2 by supercritical CO2. The results showed that the solubility of tea polyphenols in supercritical CO2 was very low, and its weight fraction was only 10-6, The entrainer, the solubility can only be increased to the order of 10-6. Supercritical CO2 was added with 3.63% aqueous ethanol solution as entrainer under the condition of 80 ℃ and 21Mpa for extraction of green tea for 1h, the extraction rate was only 0.215%. In addition to the above described several aspects, the supercritical fluid extraction technology has also been applied to the extraction of essential oils of tea flowers, tea seed oil extraction and refining and so on.