Application of Supercritical Fluid Extraction in Natural Pigments

Food pigments are an important part of food additives. They are not only widely used in food industry to improve the color of food, but also widely used in medicine and cosmetics.

Before the mid-19th century, people used natural pigments to colour. Since W. H. Perkins invented the first synthetic organic pigments aniline violet in 1856, many organic pigments have been synthesized one after another. Because of its bright color, stable property and low cost, this kind of pigments soon replaced natural pigments. With the development of science, it has been found that many synthetic pigments are harmful to human body. In addition to its own chemical properties endangering human health, and in the synthesis process, it may also be contaminated by arsenic, aluminum and other harmful substances. Therefore, many synthetic pigments have been banned in the world. According to statistics, there are 90 kinds of synthetic pigments used as food in the world, but only a dozen kinds of synthetic pigments are still widely used in many countries. Some countries, such as Norway, have completely banned the use of any synthetic pigments. Only carmine, amaranth, lemon yellow, indigo and Ridonghuang are the synthetic pigments approved for use in China. In this case, people's interest in natural pigments has greatly increased, and recent studies have found that most natural pigments have certain physiological functions, such as natural beta-carotene in the prevention of cancer, cancer and cardiovascular disease has obvious effect; alpha-carotene has good anti-cancer effect on adrenal adenocarcinoma, gastric cancer, uterine cancer, and its effect is greater than that of beta-carotene. Lycopene has the strongest antioxidant activity in carotenoids, and its effect of disease prevention and resistance is better than beta and alpha-carotene. Anthocyanins can treat circulatory disorders and angina pectoris. Functional natural pigments not only give food bright and lifelike luster, but also have health care function for human body, which accords with the general trend of modern functional food development, and is a new trend of natural pigments development.

Over the past decade, China's edible natural pigments industry has developed. There are dozens of enterprises producing natural pigments and dozens of products in China. However, almost all enterprises adopt the traditional production technology, the product quality is poor, the purity is low, there are odors and solvent residues, seriously affecting the promotion and application of natural pigments. Although a few factories export natural pigments, most of them are supplied to foreign merchants cheaply by semi-finished products such as chili oleoresin, and then used advanced separation technology abroad, except impurities and odors, they are sold at a high price. Therefore, how to use advanced equipment and technology to improve product quality is an important issue for the future development of natural pigments in China.

Supercritical fluid extraction (SFE) is a new extraction and separation technology in food industry. Compared with the traditional chemical solvent extraction method, its advantages are no chemical solvent consumption and residue, no pollution, avoiding thermal degradation of extracts at high temperature, protecting the activity of physiological active substances and maintaining the natural flavor of extracts, etc. The application of supercritical fluid extraction (SFE) in natural pigments is introduced.

2. Supercritical fluid extraction

Supercritical fluid extraction (SFE) is a process in which a fluid above the critical temperature and pressure is used as a solvent. Fluids near the critical point not only have very high solubility for substances, but also the solubility of substances varies with the change of pressure or temperature of the system, so that selective extraction and separation of substances can be easily carried out by adjusting the pressure or temperature of the system.

Supercritical fluid extraction (SFE) has been used in food industry for nearly 20 years. Zosel first studied the removal of caffeine from coffee by supercritical fluid extraction (SFE) in 1974. In 1978, Hag A. G first established the industrial equipment and technology for removing caffeine from coffee beans, which is an important milestone in the application of SFE to food industry. At present, supercritical fluid extraction has been widely used in extraction separation of oils, cholesterol, flavors and fragrances and pigments.

Supercritical fluid extraction (SFE) almost uses CO2 as extractant in food processing. CO2 is not only a strong solvent, it can extract a wide range of compounds in food processing, but also relatively stable, cheap, non-toxic, non-combustible and recyclable. The cost of CO2 production is low, and high purity gas can be obtained without residue. The critical point of CO2 is low, the critical temperature is 31.1 C, and the critical pressure is 7.38 MPa, so it is especially suitable for extracting volatile and thermosensitive substances. Compared with the traditional solvents n-hexane and dichloromethane, it has significant advantages.

Application of Supercritical Fluid Extraction in Natural Pigments

Supercritical CO2 has similar polarity to n-hexane, so it is especially suitable for extracting lipid-soluble components. Such as beta-carotene, capsaicin, tobacco tree orange, lutein and so on. In addition, by using different entrainers, the polarity of CO2 can be changed, so that the extraction range can be expanded, and more polar pigments such as tea polyphenols, ginkgo flavonoids can be extracted.

1. In the past, supercritical CO2 extraction of carotene mainly used n-hexane and other organic solvents, which not only consumed a large number of solvents, but also had to remove all solvents to avoid the toxicity caused by solvent residues. Supercritical CO2 extraction can replace the traditional solvent method to extract carotene effectively. Yu Enping used supercritical CO2 to extract carotene from seaweed. Using acetone as entrainer can improve the extraction rate. Table 1 shows the solubility and extraction rate of carotene in CO2 under different acetone content. Table 1 Solubility and extraction rate of carotene in CO2 (with acetone as entrainer)

2. Supercritical fluid extraction (SFE) of capsaicin capsaicin is used to extract capsaicin from capsicum powder with ethanol or n-hexane. After separation of capsaicin, capsaicin-free oleoresin can be obtained. After separation of capsaicin, capsaicin, an oil-like liquid with no hot and dark red color, capsaicin, can be obtained. Because of the oil-like properties of capsaicin, the removal of residual solvents (e.g. n-hexane) from solvent-extracted products is difficult to meet FAO and WHO standards, which greatly affects the use and export of capsaicin. Zhao Yaping used supercritical CO2 to extract Capsanthin from crushed dry pepper. The optimum extraction conditions were as follows: particle size < 1.2mm, pressure 15 MPa, extraction temperature 50 C, flow rate 6 M3/hr. The capsaicin extracted from red-tip pepper (containing more than 10 000 mg/kg of solvent) was purified by Wushu Zeng et al. The optimum extraction conditions were 18 Mpa, 25 C and 2.0 L/min flow rate. Residual solvents can reach below 20 mg/kg.

3. Supercritical CO2 extraction of carmine orange A. J. Degnan et al. studied the effect of supercritical CO2 on the extraction of carmine orange. The maximum solubility of pure carmine orange in CO2 was 0.003 mg/g, while that of carmine seed pigment was 0.026 mg/g. The solubility of pigments in CO2 increases with increasing temperature, but does not increase with increasing pressure at the same temperature (Table 3). Vegetable oil as entrainer can improve the extraction rate of carmine orange.

Roy R. Chao et al. extracted natural pigments from carmine seeds by supercritical CO2. The results showed that the main pigments were carmine orange and norcarmine orange. Carmine orange is easier to extract than carmine orange. Carmine orange is easier to extract than Carmine orange. The higher total pigment yield can be obtained at extraction temperature of 50 C and pressure of 310bar.

IV. CONCLUSION

Although supercritical fluid extraction (SFE) of natural pigments has many advantages, it has not been widely industrialized in China. The main reason is that supercritical equipment has a large one-time investment, and the extraction process of natural pigments is not yet mature. However, due to the advantages of supercritical fluid extraction, many manufacturers have invested or are preparing to buy supercritical equipment. Supercritical fluid extraction (SFE) of natural pigments is a key point in the future. Especially with people's recognition and attention to functional natural pigments, it is believed that supercritical fluid extraction will replace the traditional solvent method to extract natural pigments and produce high purity and high quality pigments to meet the needs of use and export.

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