At present, there is no general separation method for the full chromatographic analysis of volatile flavor substances. However, some separation technologies have been established, including liquid-liquid separation, liquid-solid separation, solid-phase extraction, rapid solvent extraction, headspace analysis, air extraction, direct thermal desorption and so on. These techniques have been used for many years, but other sample preparation methods have only recently begun to be used.
Application of new technology
Solid phase microextraction (SPME)
Solid-phase microextraction technology, which appeared in the late 1980s and early 1990s and gradually developed, is more and more widely used in gas chromatography analysis to analyze some nonvolatile or semi-volatile organic components in water or liquid extracts.
The technology includes extracting organic analytes directly from the headspace of liquid samples or sealed test tubes and transferring them to molten time-sensitive fibers coated with liquid polymers, dimethylsiloxane polymers and polyacrylates. When the equilibrium is reached, the fiber adsorbed by the substance to be analyzed is taken out, thermally desorbed in a thermal syringe, and analyzed by gas chromatography. Then select appropriate detectors and devices for gas chromatography analysis.
The technology is simple and rapid, and no organic solvent is needed in the process of sample preparation and cleaning, so no organic solvent will be discharged into the environment. It has been widely used in the experiment of determining the flavor components of flour, tea, coffee, condiments, beer, liquor, fruit juice, fruity drinks and milk. At the same time, it can also be combined with other experimental methods, such as chromatography, spectroscopy, thermal desorption, mass spectrometry and so on.
Supercritical CO2 high pressure extraction method
In recent years, supercritical carbon dioxide technology has been widely used in industry and has become a general standard. When pressurized carbon dioxide is heated above the critical temperature, it will become a supercritical liquid with some properties of gas phase and liquid phase. For example, it can easily pass through the sample and extract liquid, which is very similar to gas. It is similar to liquid in that it can dissolve a lot of fat (especially under high pressure).
According to this principle, food samples are heated in a pressurized chamber and then mixed with supercritical carbon dioxide. Carbon dioxide will extract fat and form a separable solvent layer. After chromatography, the solvent layer is decompressed, and carbon dioxide will turn into gas and run away, and the remaining fraction is fat.
An example of the industrial application of this technology is decaffeination in coffee and tea production. Recently, this extraction method has also been applied to extract the chemical components of spices and perfumes from natural products. Because of mild preparation conditions, this technology is especially suitable for extracting essential oil from spices, flowers, herbs, leaves, seeds and roots. Like solid-phase microextraction technology, it also has the advantage of avoiding environmental pollution caused by organic solvents.
Solvent-assisted distillation technology
Wolfgang Engel, Wolfgang Bahr and P. Schieberle invented a new distillation technology in 1999, called solvent-assisted distillation (SAFE), which was used to extract volatile flavor components from complex liquid phases such as beer, fruit juice, milk and cheese. In the experiment, both the distillation bottle and the fractionating tube were kept in a low temperature environment (20℃~30℃) to avoid the polymerization of high-boiling compounds, and the sample was quantitatively dropped into the pouring bottle from the funnel to reduce the extraction time.
The inventor of this technology also pointed out that this method has high yield for extracting volatile and polar flavor compounds and flavor substances from samples including fat. Liquid samples such as milk, beer and orange juice can be distilled directly in this way, and the samples with reduced flavor feel very close to the original samples.
Equipment and auxiliary supplies
explorer
Evaporative light scattering detector, ELSD 800 can be used to replace or assist the detector in liquid chromatography system. It can quantitatively detect non-volatile or semi-volatile analytes in samples. This detector is also used to detect liquids, carbohydrates, fatty acids and amino acids. According to the manufacturer, this detector is more accurate than the ultraviolet detector, and can be combined with mass spectrometry to obtain information on composition and content.
Gas chromatographic olfactory system, Sniffer 9000 is a special sniffer, which can cooperate with any gas chromatographic analysis. In the past decades, many detection technologies have been related to gas chromatography. GC/O, a system with human nose as detector, has been neglected for a long time. However, the human nose is usually more sensitive than any physical detector. GC/O system has a wide range of applicability, for example, it can be used to detect the taste of food, perfume and any odorous items (such as pollutants).
Smelling technology can test the influence of food smell on people. There are usually two methods: one is dilution method, which is based on continuously diluting an odor until it can't be felt at the olfactory mouth. The other is intensity method, in which the odor substance is injected only once, and the experimenter records the changes of odor intensity at different times.
Blowing and suction equipment and headspace equipment
These two devices are mainly used to monitor odor volatilization in food packaging and beverage detection. The new purging and trapping speed XPTTM equipment is very suitable for monitoring the volatilization of food and beverage odor. The product is being patented, and it has a positive locking chamber, which can provide effective desorption, especially for compounds with higher boiling point. The sample channel can prevent the loss of sample activity, polarity or high boiling point compounds. Other efficient and time-saving functions include electronic flow control, pressure monitoring and automatic leak detection.
Electronic nose detector
Znase is said to be the only electronic nose that can distinguish and measure the components of each compound within 10 second. Based on chromatography technology, it can create chromatograms, virtual chemical sensors or two-dimensional images. Portable design can be used in laboratory and field. The equipment can also be used as a shielding tool to reduce the influence of negative factors in the laboratory.
SPME is a set of auxiliary equipment, including Alpha MOS sensor array, mass spectrometry and electronic nose detector. It is used to improve sensitivity, extend detection limit, enhance selectivity, improve repeatability and improve analysis speed (average 2 ~ 15 minutes).
Cyranose electronic nose detector is mainly used for food, packaging and fragrance detection, and may have special applications in specific industries. Mainly used in comparative experiments, a typical steam can be measured and recorded as a standard digital model, and then in the subsequent detection process, the sample is compared with the standard model to determine whether it is the same substance. The polymer compound detector of this equipment can detect a variety of organic compounds, bacteria and natural products.
Gas chromatographic analysis
GC- 17A chromatograph can provide necessary parameters for most applications. The system can ensure the repeatability of all operating parameters, including carrier gas flow, split ratio, heating zone temperature, make-up gas flow, detector output range and current. The flow control and pressure control of the carrier gas flow can be carried out at the same time (at most 14 channels). You can enter at most 10 GC parameter files, and GC can be directly controlled by keyboard. All parameters are managed by the built-in password system, and the key parameters can be controlled by permissions.