Astaxanthin is a red pigment widely present in living organisms and has very strong antioxidant properties. Natural astaxanthin is known as the “King of Antioxidants” in nature in the 21st century. Its antioxidant capacity is 6,000 times that of vitamin C and 1,000 times that of vitamin E.
Ⅰ.What is astaxanthin?
Astaxanthin, also known as metaphycoxanthin or astaxanthin, is a terpene unsaturated compound. Its chemical name is 3,3′-dihydroxy-4,4′-diketo-β. β′-Carotene, the molecular formula is C40H52O4. Under the condition of 100kPa, the melting point is 216°C and the boiling point is 774°C.
Astaxanthin is widely found in animals (such as aquatic animals, birds), plants, fungi, algae and bacteria. It has obvious benefits to human health and is known as the “Red Miracle”. Currently, astaxanthin is packaged as a health food and sold in the market. It has antioxidant, anti-aging, anti-tumor, and prevention of cardiovascular and cerebrovascular diseases.
Ⅱ.How astaxanthin is produced
1. Chemical synthesis method
According to the difference in synthesis methods, the synthesis methods of astaxanthin are divided into two types. One is the indirect synthesis method, which is obtained by oxidation of other carotenoids; the other is the direct synthesis method, which is directly obtained from commonly used synthetic carotenoid monomers. synthesis.
Chemically synthesized astaxanthin has the advantages of low production cost, high yield, and astaxanthin purity of more than 96%. However, the absorption and utilization rate of the synthesized astaxanthin in the body is low, and the stability, safety and anti- The oxidative activity is lower than that of naturally extracted astaxanthin.
2. Natural extraction method
Natural astaxanthin is mostly found in marine organisms. The natural extraction method is to crush astaxanthin-rich processing by-products such as shrimps and crabs, remove lime, and use organic solvents to extract astaxanthin. This method can promote the development of the breeding industry and reduce the environmental pollution caused by waste aquatic product by-products. However, due to the high ash and chitin content in the carapace of discarded shrimps and crabs, and the low astaxanthin content, the extraction process is complicated and the extraction cost is high.
3. Microbial fermentation method
The method of producing astaxanthin using yeast, algae and bacteria is called microbial fermentation. The main bacterial species include the unicellular green algae Haematococcus pluvialis, Chlorella aeruginosa, Phaffia rhodopsin, Rhodotorula rhododendron, Rhodotorula glans and Paracoccus spp.
Astaxanthin produced by fermentation method has a clear structure, few by-products and is environmentally friendly. However, it is restricted by factors such as low yield, strict requirements for culture conditions, and high culture costs. The key factors in the production of astaxanthin by microbial fermentation are the use of cheap culture raw materials and the selection of high-quality, high-yielding strains so that they can be used in industrial production.
Ⅲ.Astaxanthin-producing microorganisms
1. AlgaeMany algae can produce astaxanthin, such as Haematococcus pluvialis, Chlamydomonas, Umbrella algae, Euglena algae, etc. Haematococcus pluvialis is a freshwater single-cell green algae. The astaxanthin in its cell mainly exists in the form of double-esterified astaxanthin and mono-esterified astaxanthin, and a small amount exists in free form. It is produced by astaxanthin. Main algae.
However, the growth time of Haematococcus pluvialis is long, the culture conditions are strict, it needs light, and the production site is limited. Moreover, astaxanthin exists in thick-walled spores, so the extraction rate is low and the continuity is poor.
2. BacteriaAstaxanthin exists in various bacteria such as Brevibacterium, Paracoccus, and Mycobacterium lactis. Although the astaxanthin content of most bacteria is much lower than that of algae and Phaffia rhodozyma, the problem of low astaxanthin production in bacteria can be improved by introducing genes related to astaxanthin synthesis into bacteria.
The production of astaxanthin through bacterial fermentation can significantly reduce the production cost of natural astaxanthin, which is of great significance to the future industrial production of astaxanthin.
3. YeastYeast fermentation produces astaxanthin, and the main strains used include Phaffia rhodopsin, Rhodotorula rhododendron, marine Rhodotorula and crimson yeast. The production of astaxanthin by Phaffia rhodozyma has the following advantages:
·A variety of carbon and nitrogen sources can be used to produce astaxanthin
·Cells grow and reproduce quickly, enabling high-density culture
·Short productioncycle and low cost
·It is easy to be absorbed by the human body. After extraction, the yeast cells can be directly used as feed additives.
The pathway of yeast biosynthesis of astaxanthin is divided into two stages: the first stage is the synthesis of β-carotene; the second stage is the production of astaxanthin through oxidation and hydroxylation of β-carotene. The synthesis pathway of yeast astaxanthin is as follows:
Ⅳ.Purification method of astaxanthin
1. Astaxanthin wall-breaking treatment method
Astaxanthin is an intracellular product and generally needs to be broken down, extracted and purified before it can be extracted from yeast cells. Commonly used wall breaking methods include mechanical methods, chemical methods, enzymatic hydrolysis methods and heat treatment.
The mechanical method uses mechanical equipment to tear the cell wall and release the contents through intracellular osmotic pressure. The main methods include ultrasonic disruption, bead grinding, spray impact disruption and high-pressure homogenization. The operation is simple, but it can easily cause the solution temperature to be too high in some locations, resulting in the loss of astaxanthin.
Chemical methods mainly include dimethyl sulfoxide method, acid-base heating method and organic solvent infiltration. Alkaline extraction and acid hydrolysis require a large amount of alkali and organic acids to break the wall, which increases sewage discharge and causes environmental pollution, and strong acids and alkalis can cause damage to astaxanthin. Using a lactic acid concentration of 5.55 mol/L and a crushing temperature of 30°C for wall-breaking extraction can reduce the damage to astaxanthin.
The enzymatic hydrolysis method has mild treatment conditions, low requirements for equipment, and the treatment process causes less pollution to the environment. The extracted astaxanthin is more stable than that obtained by other methods.
Currently, a variety of modern extraction methods have been developed for extracting active components, such as pulsed electric fields, high-voltage microfluidization, ionic liquids and other emerging technologies.
2. Extraction method of astaxanthin
Astaxanthin is a fat-soluble substance that is soluble in organic solvents and insoluble in water. It can be extracted with polar organic solvents such as acetone, ethanol, methanol, and petroleum ether. Since the extraction effect of a single solvent is limited, the researchers found that the astaxanthin content extracted by the acid-thermal method using a 2:1 mixed solution of ethyl acetate and ethanol as the extractant was significantly higher than the extraction effect of a single solution.
3. Purification and detection methods of astaxanthin
Thin layer chromatography and column chromatography are mainly used to purify astaxanthin. Thin layer chromatography can be used to simply determine the components of the crude extract. Column chromatography is the most effective method because of its cheap equipment and convenient replacement of stationary phase and mobile phase. Commonly used purification methods.
Thin layer chromatography and column chromatography are suitable for the early purification process. Preparative high-performance liquid chromatography can be used for later purification to achieve a purification effect of more than 98%, but the preparation cost is high. In order to quickly determine the production of astaxanthin in experiments, UV-visible spectrophotometry is usually used.