Alkaloids are an important class of natural organic compounds, which are widely distributed in the plant kingdom and possess a variety of biological activities. Many important botanicals mainly contain alkaloids.
Research status of supercritical CO2 fluid extraction of alkaloids
In recent years, there have been many reports on the extraction of alkaloids from traditional Chinese medicine by supercritical fluid extraction technology:
Rhizoma Coptidis extract alkaloids
Tong Ruofei et al. used supercritical CO2 to extract alkaloids from Coptis chinensis. The optimal extraction process conditions were 30MPa extraction pressure, 40-60 mesh material size, extraction temperature 60℃, and extraction time 1.5h. Under these conditions, the extraction rate of alkaloids from Rhizoma Coptidis was 14.24%.
Supercritical CO2 extraction of theophylline alkaloids
Wang Taoyun established a supercritical extraction process for theophylloalkaloids. The optimal process conditions are at an extraction pressure of 40MPa, an extraction time of 0.5 h, and an extraction temperature of 45°C. The extraction rate of theophylloalkaloids is 1.14%.
CO2 extraction of vinca alkaloids
Arvind Verma et al. used supercritical technology to extract Catharanthus roseus alkaloids from Catharanthus roseus plants. The most suitable process conditions are extraction pressure 25MPa, extraction time 40min, extraction temperature 80°C, entrainer methanol, and extraction rate 4.1%.
CO2 extraction of free and tea alkaloids
WEI-QIANG TANG et al. used supercritical fluid to remove caffeine in green tea, and the removal rate reached 83.28%.
Zhang Liang et al. used supercritical CO2 fluid extraction technology to extract free alkaloids from Fritillaria cirrhosa, and optimized the extraction process through orthogonal design, namely, the extraction pressure was 20 MPa, the amount of ethanol was 300 mL, the extraction time was 2 h, the extraction temperature was 45 ℃, and the extraction rate was up to 0.195%.
Zhao Songliang et al. used supercritical CO2 fluid to extract the total alkaloids in Chrysanthemum Notoginseng. The optimal process conditions are the extraction pressure of 25MPa, the extraction temperature of 60℃, the extraction time of 3 h, and the amount of ethanol 200 mL. Under these conditions, the alkaloids can be obtained. The rate is 0.192%.
Chrysanthemum total alkaloids
Zheng Pinmei uses pepper as the raw material to study the suitable conditions of the piperine process by supercritical carbon dioxide extraction. The preliminary determined suitable conditions are the extraction temperature of 45℃, the extraction pressure of 17MPa, the analysis temperature of 60℃, and 75% ethanol as the entrainer. , The extraction rate is 3%.
Hu Jinghong applies supercritical CO2 fluid technology to obtain a higher yield of total alkalis of matrine, which is an environmentally friendly process route that combines supercritical oil removal and solvent extraction to extract the total alkalis of matrine in matrine. The total alkali yield is compared with the direct solvent method. The extraction ratio is improved by nearly 1.5 times.
It can be seen from the above that the supercritical CO2 fluid extraction technology has been successfully applied to the extraction of a variety of alkaloids in Chinese herbal medicines, and the operation process is easy to control. In the future, the supercritical fluid technology will be more applied to the extraction of Chinese herbal medicines and has been developed by leaps and bounds.
Influencing factors of supercritical fluid extraction of alkaloids
At present, the separation of alkaloids using supercritical fluid extraction technology is more difficult than the separation of other components such as volatile oil.
The main reason is that most of the alkaloids are polar. Most of the alkaloid compounds are combined with organic acids to form salts and exist in plants, and some are combined with some special acids. Among them, only a few alkaloids are weakly alkaline or It is very weak, difficult or unable to combine with acid to form a stable salt, which may exist in plant tissues in the form of free alkali.
Therefore, various factors must be comprehensively considered when supercritical extraction is carried out in order to achieve a better separation effect.
Focus on the following aspects of the effect and application of supercritical CO2 fluid extraction of alkaloids.
Extraction temperature and pressure temperature
Extraction temperature and extraction pressure are the basic influencing factors of supercritical extraction.
It is also the main parameter for the separation and extraction of alkaloids.
E. Stahl once pointed out that the carbon dioxide pressure is in the range of 8~200MPa, the solubility of solute in carbon dioxide is proportional to the density of carbon dioxide, and the density is related to temperature and pressure.
Arvind Verma et al. used the effect surface optimization method to extract the vinca alkaloids from the Catharanthus roseus plant. The effect surface shows that pressure and temperature have a very significant influence on the separation effect.
For some substances containing strong polar groups such as hydroxyl, carboxyl, and phenylhydroxyl groups, higher temperature or pressure is required. For example, the extraction pressure for isoquinoline alkaloids in Nelumbo nucifera Gaertn is 45MPa, and the extraction temperature is 70°C. The extraction pressure required for the medium alkaloid is 35MPa and the extraction temperature is 60°C.
Cai Jianguo et al. investigated the effect of changes in extraction pressure and extraction temperature on the extraction rate of total alkaloids in the study of supercritical CO2 extraction and extraction of total alkaloids. The extraction rate of total alkaloids increased with pressure at a temperature of 308.15K. The change is small, and at 313.15K and 318.15K, when the pressure is from 15.0MPa to 25.0MPa, the total alkaloid extraction rate increases faster, increasing from 0.01%, 0.003% to 0.035%, 0.04%, respectively; when the pressure exceeds 25.0 After MPa, the increasing trend of total alkaloid extraction rate slows down.
This is because in the low pressure area, a small pressure increase will result in a significant increase in density, while in the high pressure area this effect is relatively weakened.
For the temperature, the increase in temperature will cause the increase of the vapor pressure of the solute, which is beneficial to the extraction operation, but at the same time it will also cause the density of the supercritical fluid to decrease, the dissolution ability is reduced, and the separation effect is deteriorated.
For the application of supercritical extraction technology to separate alkaloids from plants, it is advantageous to adopt higher pressure and temperature due to the tighter binding of alkaloids in plants.
When supercritically extracting alkaloids, the binding state of the alkaloids in plant tissues must be considered, and most alkaloids exist in the tissue plants in the form of salt.
The purpose of using an alkalizing agent to treat the raw materials is to convert the alkaloid salt originally combined with the acid into a free state, reduce the degree of contact between the alkaloid and plant tissues, and thereby improve the extraction efficiency.
Commonly used alkalizing agent
Commonly used alkalizing agents include ammonia water, triethylamine, Ca (OH)2, Na2CO3 solution, etc. Zhang Liwei and others first treated Sophora flavescens with ammonia water and then extracted the total alkaloids of Sophora flavescens with supercritical flavonoids.
Zhang Chunjiang also used ammonia water to extract the arecoline components in betel nut.
Extract after alkalization.
The research by Liang Baozuan and others on the SFE and content determination of the total alkaloids of Yadong Aconitum showed that the yield of the total alkaloids of aconitum without alkalization was 14.12%, and the yield after alkalization was 26.6%. It can be seen that the effect is significantly improved after alkalization.
Zhao Songliang did not add the alkalizing reagent to the alkaloids of Duchangju Panax notoginseng during the separation
The extraction yield was 7.36% and the extraction yield increased to 13.27% after the addition of alkalizing reagents, and the total yield increased by about 80%.
Yang Jing used supercritical CO2 extraction technology to separate the alkaloids from the heart of lotus seeds.
A study was conducted, and the extraction rates of liensinine were 0.086%, 0.047%, and 0.127% with sodium carbonate solution, ammonia water, and calcium hydroxide as alkalizing agents.
The reason for using ammonia as an alkalizing agent may be that during the alkalization process, the alkalinity of the ammonia water is strong, and the liquid is easy to mix with supercritical CO2 fluid, and the alkalization effect is good.
However, ammonia water and triethylamine are both liquid and strong alkaline, which has certain influence on supercritical equipment.
The corrosive effect.
In contrast, the use of weakly alkaline solid Ca(OH)2 has relatively little corrosive effect.
Most of the solvents for supercritical fluid extraction are non-polar or weakly polar, and have greater solubility for lipophilic substances, while most of the alkaloid components are polar. In the process of extracting alkaloids, adding a suitable entrainer is not only It can improve the solubility of alkaloids, but also improve the selectivity of extraction and increase the purity of alkaloid components.
Commonly used co-solvents
Commonly used co-solvents are mostly organic solvents such as methanol, ethanol, acetone, and chloroform.
External water, organic acids, organic bases, etc. can also be used as auxiliary solvents.
When Qiang Limin used supercritical CO2 fluid to extract matrine, he investigated the dynamic addition
Add acetone, methanol, ethanol, Tween, ammonia and other co-solvents, and determine the appropriate co-solvent combination as ethanol, Tween-80, and the volume ratio of distilled water is 12:1:7.
Janicot et al. used CO2:CH3OH:H2O (mass ratio 70:24:6) as a cosolvent. Under the conditions of 20 MPa and 45°C, codeine, morphine and thebaine can be extracted from poppy stems after 20 minutes Etc. 5 kinds of alkaloids.
Heemann Volker et al. added 6% (mass percentage) citric acid to separate the nicotine in tobacco under the conditions of 70°C and 25MPa, and the content of nicotine in tobacco decreased from 1.98% by 0.20%.
How to add co-solvent
There are two ways to add co-solvent: static addition and dynamic addition.
When extracting strychnine, Kevin et al. combined the two methods. First, methanol was used as a co-solvent for static extraction, and then the co-solvent chloroform was dynamically added for extraction. The extraction efficiency was higher than that of using methanol or chloroform as the co-solvent alone.
The use of co-solvent improves the solubility of the active ingredients in the solvent, broadens the extraction range, and improves the extraction efficiency. Young Hae ChoP et al. [have investigated the influence of different ratios of methanol, water, and triethylamine on the extraction rate of tricephrine, and the results showed that the extraction rate of trichampine was 3.7% when combined with methanol and triethylamine. Therefore, it is a good way to add an appropriate amount of solvent as an entrainer to the CO2-SFE system to increase the dissolving power of CO2.
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