Based on the physicochemical properties of chili pepper pigment, the industry mostly adopts the following methods for extraction. After crushing the pericarp of the mature dry fruit of the pepper of the Solanaceae plant, it is extracted with ethanol, acetone, isopropanol or hexane. Considering that natural red pepper contains capsaicin, capsaicinoids, capsaicinoids and other components, of which capsaicin, or capsaicinoids, has a spicy taste and produces irritating vapors at high temperatures, it must be removed in the refining process of capsaicinoids. Structurally capsaicin contains an amide bond and a hydroxyl group in the molecule, it is a polar compound, and its crystals appear as monoclinic prisms or rectangles, with a melting point of 61°C. It is soluble in solvents such as dilute ethanol, hexyl ether, acetone, ethyl acetate, and in alkaline aqueous solutions. Considering the different solubility of paprika mixture and capsaicin in different solvents, the difference in solubility of the two can be utilized for dehazing.
He Wenzhi et al. based on this principle of n-hexane extraction method, the use of chili red pigment is easy to dissolve in n-hexane and capsaicin is more difficult to dissolve in n-hexane the nature of the two to be separated, the operating steps are as follows weighing the de-sticking, seeding, crushing treatment of red pepper powder, acetone as the extractant for the atmospheric extraction operation, the extract is at a temperature of 90 ℃, the vacuum degree of 0.09 megapascals (MPa) The extract was concentrated by distillation under reduced pressure at a temperature of 90°C and a vacuum of 0.09 MPa, and the acetone was recovered at the same time. The process of extracting paprika with acetone is essentially a mass transfer process between liquid and solid through the interphase contact surface, and the speed of the mass transfer rate determines the size of the mass transfer equipment and the operation time. In this method, in order to improve the rate of mass transfer, a Soxhlet extractor was used for the extraction of dried paprika in powder form. A certain amount of concentrated crude paprika product was weighed and extracted with a certain amount of n-hexane to remove the color. Color value was defined as the absorbance of the extract per unit mass of raw material.
The method is simple, the pigment recovery is large, the product yield is high, but the product color value is small. As the negative correlation between color value and spiciness indicates that the method is not thorough enough to remove the spiciness, it can be used for the case where chili red is the main product and the requirement of capsaicin content is not very demanding. Zhang Zong'en et al. prepared chili oleoresin by extracting acetone as a solvent, the oleoresin yield was high, the color value was large, the content of capsaicin was low, and it was easy to separate. Using acetone (50%) solution with pH greater than 10.37 for more than 5 times of de-hot extraction can be obtained by mouth without spicy red pigment. The method is simple and easy to operate, and the quality indexes of the obtained pigments are in accordance with FAO/WHO standards.
(2) Column chromatography
It is reported that capsaicin in chili peppers can still be felt as spicy even if it is diluted by 1:100000, which limits the application of chili pepper pigment to a large extent. Therefore, removing the spicy component becomes a key step in the process of extracting and isolating red pigments from chili peppers. The separation of paprika pigment by silica gel column chromatography is a partition chromatography method, which is based on the structural differences between pigment and chorine, which have different solubility in the stationary phase bound to silica gel and the eluent, and therefore different partition coefficients between the stationary phase and the eluent to achieve the separation effect. Yuan Qingyun studied the separation of chili red pigment by silica gel column chromatography, and summarized the following process:
Chili pepper→selection→crushing→enzymatic addition→filtration→concentration→ethanol and petroleum ether extraction→filtration→concentration→silica gel column→elution→concentration→deep red viscous liquid
Operating points:
1) enzyme: enzyme hydrolysis to make the pigment in the cell combined with proteins, fats, sugars and so on, to be free. out, easy to extract with solvents. ②Extraction: extract with 90% ethanol and petroleum ether (1:1) at room temperature with stirring overnight extraction, filtered and concentrated under reduced pressure. ③Through thin layer chromatography to find the elution conditions, when the volume ratio of petroleum ether and edible grade 90% ethanol = 2:1 when the best spreading layer effect. ④ The extracted concentrate was put on a silica gel column with a diameter of 10 cm and a height of 100 cm, eluted with eluent, and the red eluted fraction was collected. ⑤ The collected eluted fraction was concentrated under reduced pressure.
The red viscous liquid obtained from the experiment was examined to have a moisture content of 0.37%, a fat content of 90.68%, a pigment:color scale E1%1cm (475nm) = 143, and no capsaicin. He Wenzhi, Suo Quanling et al. also explored the column chromatography extraction and refining method of paprika red pigment: acetone was used as the extractant to extract the paprika red crude from the dried red pepper powder, and the crude was concentrated and processed by reduced-pressure distillation and then subjected to the column chromatography dehotterization and refining operation. In view of the advantages of the column chromatography method, a glass column with large size specification was used for column chromatography separation, and silica gel with a particle size of 74-152 micrometers (μm) was selected as the packing material, and a compound mixture of petroleum ether and acetone (10:1) was used as the unfolding agent for column chromatography. The crude product of paprika was separated by column elution, and the first liquid that flowed out was orange-yellow liquid (in small amount), followed by paprika red pigment, and finally, it was the yellowish liquid with strong spicy flavor that was more difficult to elute. The red pigment product was collected and concentrated by reduced pressure distillation, and its color value E 1%1cm (460nm) = 56.5 was determined by 751 spectrophotometer, and the pigment recovery could reach an average of 67.2%.
In response to the problem that most of the existing literature describes the method of extracting non-spicy mixed pigments from red chili peppers but does not further separate and analyze the mixed pigments, the separation of yellow pigments in chili pepper pigments by column chromatography was proposed. The method uses silica gel as stationary phase, acetone and 95% ethanol as eluent of hot red pigment and hot yellow pigment respectively, the amount of pigment separated each time is 4%~2% of the mass of silica gel, and the separated liquid is distilled under reduced pressure to obtain the concentrated product. Through this process, not only can we get the main by-product of chili pigment - yellow pigment, but also correspondingly improve the purity of the main components, and get the red pigment with high purity.
Using column chromatography separation technology, adsorbent X and mixed eluent were selected for pilot tests to further separate red, orange and yellow in chili pigment, which could make the color value and hue of low quality chili red pigment improved greatly. Wu Mingguang et al. used column chromatography separation technology to isolate free crystalline capsicum red pigment monomer from the peel of chili peppers with a content of more than 95%, which is a breakthrough in the dosage form of capsicum red pigment in China.
(3) Supercritical CO2 fluid extraction technology
Because of the oily properties of capsaicinoids, the use of organic solvents to extract the separation of paprika pigments obtained from the product has a higher solvent residue, take the general method of the eluent product is difficult to achieve the Food and Agriculture Organization of the United Nations and the World Health Organization (FAO/WHO, 1984), the latest standards, which greatly affected the practicality and export of paprika pigments. It is difficult to meet the latest standards set by the Food and Agriculture Organization of the United Nations and the World Health Organization (FAO/WHO, 1984) with the general eluent method. Supercritical fluid extraction is a new chemical separation technology. The key to this technology is to understand the solubility of supercritical fluids and the changing law with the influence of many factors. Supercritical CO2 fluid extraction (SCFE-CO2) is the use of higher than the critical temperature, critical pressure CO2 fluid as a solvent extraction process. Fluid in the vicinity of the critical point not only has a very high solubility of substances, and the solubility of substances will change with the system pressure or temperature changes, so that by adjusting the pressure or temperature of the system can be convenient for selective extraction and separation of different substances. The supercritical separation technology has simple process, low energy consumption, non-toxic extraction solvent, easy to recover, and the obtained products have very high purity, and the residual solvent meets the requirements of FAO/WHO. Zhao Yaping et al. used self-designed supercritical CO2 fluid extraction equipment for chili pigment extraction. The equipment is mainly composed of four parts: gas supply system, supercritical CO2 fluid generation system, extraction and separation system, and metering system, and all the parts are localized. The experiments showed that the optimal extraction conditions were particle size 〈1.2 mm, extraction pressure 15 megapascals (MPa), extraction temperature 50 ℃, and flow rate 6 m3/hour. During the extraction process, the separation effect of capsaicin and capsaicin was judged according to the absorbance curve of 200-600 nanometers (nm) measured by UV3000 ultraviolet-visible spectrophotometer. The absorbance was measured at 449 nanometers (nm) with an acetone solution of the pigment, and the obtained value was the color value of the pigment. The quality indexes of chili pigment extracted by this method exceeded the national standard.
The supercritical extraction device made by NOVA Company of Switzerland was used to separate and purify the chili pigment. The best process parameters to make the product meet the requirements of FAO/WHO residual solvent standards (hexane content ≤ 25 mg/kg) are: extraction pressure of 18 megapascals (MPa), extraction temperature of 25 ℃, extractant flow rate of 2.0 liters / min (L / min), extraction time of 3 hours (h). The color value of the product could reach 342 under the optimal process conditions.Han Yuqian et al. used supercritical CO2 fluid extraction technology to refine paprika red pigment with a color value of 100～180 and a solvent residue of 30×10-6～150×10-6, and the experimental results showed that: when the extraction pressure was controlled to be less than 20 megaPa, the color value and hue of paprika red pigment were almost unaffected by the loss of color value and the residue of organic solvent could be reduced to 2.7% and the residue of organic solvent could be reduced to 2.7%, and the extraction temperature was 25℃. residue could be reduced to about 2.7×10-6, but the red pigment and yellow pigment in the paprika pigment did not reach complete separation. It was found that the use of co-solvents such as 1% ethanol or acetone in the supercritical CO2 fluid extraction of capsicum pigments or the increase of extraction pressure could improve the yield of capsicum pigments. Almost all capsaicinoids obtained at lower pressure were β-carotene, while a larger proportion of red carotenoids such as capsaicinoid red pigment, capsaicinoid yucca pigment, zeaxanthin, β-cryptoxanthin, etc. and a small amount of β-carotene were obtained at higher pressure. In the two-step segmented extraction process, the technique of separating red chili oil and β-carotene in the first stage ensured the enrichment of chili pigment extraction in the second stage and made the ratio of chili red and yellow pigments reach to 1.8.The chili pigment de-spicing and refining technique was investigated on the self-developed multifunctional supercritical CO2 fluid extraction and fractionation device, and the results showed that the red chili pigment could be extracted at the pressure less than 10.0 MPa to extract the The results showed that the yellow and spicy components could be extracted at a pressure of less than 10.0 MPa, and the red pigment could be retained; the red component could be completely extracted when the pressure was greater than 12.0 MPa. Although supercritical fluid extraction of natural pigments has many advantages, due to the large one-time investment in supercritical equipment, it has not been widely used in this field in China.
(4) Other
The two-step extraction method is used to separate red pepper, that is, the first organic solvent extraction method is used to extract the pepper extract containing red pigment, capsaicin, and tar flavor odor from the dry tip of the pepper, and then the supercritical CO2 extraction method is used to remove the tar flavor odor and separate the red pigment from the capsaicin to get the red pigment and capsaicin which are free of organic solvents, and the yield is higher than that of the pure The yield is 5-7 times higher than that of the supercritical extraction method alone, and the quality far exceeds the FAO/WHO (1984) standard.