In 1980, the American company (Tone, s) proposed the liquid nitrogen freezing method to grind substances with high essential oil content, which successfully solved the “slip” and heating phenomenon that existed in normal temperature grinding. This technology mainly uses the characteristic that liquid nitrogen can produce a low temperature of 112°C when it is converted from liquid to gas. When processing materials, liquid nitrogen is sprayed on the surface of the materials, so that the temperature can quickly drop to one in 8 seconds. Around 70C, so that the physical properties of the material (such as brittleness, bristles, etc.) are changed, making the material easier to crush. Compared with normal temperature grinding, liquid nitrogen freezing grinding has a low grinding temperature, which can reduce the volatility of the main flavoring substances; liquid nitrogen surrounds the spices and minimizes the oxidative deterioration of flavor components; changes the physical structure of the ground spices, So that it can get better protection in the product and other advantages.
Microwave radiation-induced extraction method:
Microwave radiation-induced extraction of aromatic plant essential oils is a new achievement in industrial microwave applications. The basic principle is that the microwave directly interacts with the separated substance, and the activation of the microwave causes the reaction difference of different components in the sample matrix to separate the extracted substance from the matrix quickly, and a higher yield can be achieved. Non-polar solvents are generally selected for extracting essential oils from plant materials. Non-polar solvents have a small dielectric constant and are transparent or translucent to microwaves, so that microwaves can freely pass through the solvent to reach the inside of the plant. There are many factors that affect microwave extraction. The main factors are the extraction solvent, extraction time, extraction temperature, and moisture and humidity in the sample. The polarity of the solvent has a great influence on the extraction efficiency. In addition to considering the polarity of the solvent when performing microwave extraction, it is also necessary to consider various factors such as the solvent’s strong ability to dissolve the separated components and less disturbance to the subsequent operations of the extracted components. It has been reported that the solvents used for microwave extraction include methanol, ethanol, isopropanol, acetone, acetic acid, dichloromethane, n-hexane, acetonitrile, benzene, toluene, etc. The microwave extraction time is related to the measured sample volume, solvent volume, and heating power, and is generally 10 to 15 minutes. Some research results show that the extraction recovery rate increases with the extension of the extraction time, but the increase is not large and can be ignored. In a closed microwave extraction vessel, because the internal pressure can reach more than ten atmospheres, the boiling point of the solvent is higher than the boiling point of the solvent under normal pressure. Therefore, the microwave extraction can reach the extraction temperature that can not be reached with the same solvent under normal pressure. In order to improve the extraction efficiency, but not to decompose the extract to be tested. The tendency of extraction recovery rate to increase with increasing temperature is only manifested in a not too high temperature range, and the optimal extraction recovery temperature of each substance is different. The water content of the material has a great influence on the extraction recovery rate. Because moisture can effectively absorb microwaves and produce a temperature difference, for materials that do not contain moisture, the method of re-wetting should be adopted to make it have suitable moisture. Although the application research of this technology in the food extraction industry and chemical industry has only been a few years, it has developed rapidly. Compared with conventional distillation and extraction methods, it has obvious advantages. Microwave extraction can effectively lift up useful components in materials; rapid reaction or extraction, high yield; time-saving, high selectivity for extracts; low energy consumption and solvent The dosage is small, which is conducive to the extraction of substances that are unstable to heat; the production line combination is simple and investment is saved; there is no pollution. The disadvantage is that only part of the main components can be obtained, and the composition of the finished product is unstable. For volatile components, microwave extraction can lift them more quickly and safely, and the volatile components are gradually lost with the extraction time.
Accelerated solvent extraction technology:
A brand-new extraction method proposed by Richter et al. in 1995 during accelerated solvent extraction is the automatic extraction of organic solvents by increasing the temperature and pressure. It is a standard method recommended by the US Environmental Protection Agency. Compared with its extraction method, it has the advantages of less solvent consumption, rapidity, little influence of the matrix, high efficiency and high selectivity. At present, it is mainly used in the fields of analysis, medicine, food, etc., but it is rarely used in natural products, and further organic development is needed.
Ultrasonic extraction method:
Ultrasonic extraction technology uses the strong cavitation effect, mechanical vibration, high acceleration, emulsification, diffusion, crushing and stirring effects produced by ultrasonic waves to increase the frequency and speed of the movement of material molecules and increase solvent penetration , So as to accelerate the effective ingredients into the solvent and promote the extraction method. Ultrasonic extraction has the advantages of short extraction time, high yield, and mild conditions. In the ultrasonic extraction operation, attention should be paid to the selection of extraction temperature, solvent, and ultrasonic intensity, frequency and time. Different extraction objects and different parameters will have different results. Even for the same extraction object, improper selection of parameters may not provide or get good results. When the sound intensity is high, the output is low and the fragrance becomes worse. Ultrasonic extraction is now mainly used in the food industry and the extraction of active ingredients in traditional Chinese medicine, and has broad application prospects.
Chromatography: Chromatography can be divided into thin layer chromatography, column chromatography and countercurrent chromatography. The components of natural flavors can be divided into volatile and non-volatile, and different chromatographic extraction and separation can be selected according to the nature of the components. For volatile components, gas chromatography is still the most commonly used separation method. Gas chromatography packed column is used to separate aroma components, the column efficiency is not high, capillary column has become the main column type for aroma component separation. The separation of non-volatile components is mainly thin-layer chromatography and high-performance liquid chromatography. Liquid chromatography fluids have a slow separation speed due to their high viscosity and low diffusion coefficient. The combination of liquid chromatography and spectroscopy technology can achieve the purpose of rapid screening of natural products. Combined with ultraviolet spectroscopy, mass spectroscopy, and nuclear magnetic resonance spectroscopy, it can achieve simultaneous separation and component structure analysis. Supercritical fluid chromatography overcomes the shortcomings of gas and liquid chromatography and has good application prospects.