What Is Astaxanthin Good For?

Currently, the main colorants added to aquaculture are natural colorants and chemically synthesized carotenoids. Natural colorants refer to extracts from animals, plants, and microorganisms that are rich in carotenoids and lutein. Chemically synthesized carotenoids include carotenoid and lutein. Astaxanthin can be extracted naturally or synthesized chemically. It is an oxygen-containing derivative of carotenoids and is now one of the most widely used feed colorants in aquaculture. This article describes the structure, properties, production methods, application effects in aquaculture, and development prospects of astaxanthin.

1 Structure and physical and chemical properties of astaxanthin

Astaxanthin, also known as shrimp yellow, has the chemical name 3,3'-dihydroxy-4,4'-dione-beta,beta'-carotene with the molecular formula C40 H52 O4. It is a keto-type carotene containing two hydroxyl groups (—OH) and two keto groups (=O). Most of its natural forms exist as esters.

Astaxanthin is an oxygen-containing organic compound with a pink color. It is insoluble in water, but soluble in most organic solvents. It is unstable in the presence of acids, oxygen, high temperatures and ultraviolet light, and is easily oxidized and degraded.

2. Astaxanthin production methods

There are two main methods of astaxanthin production: natural extraction and chemical synthesis.

2.1 Natural extraction of astaxanthin

Natural astaxanthin is often found in certain animals, algae and microorganisms. Its production can be divided into extraction from animals and their by-products, extraction from algae and microbial fermentation.

2.1.1 Extraction from animals and their by-products

Astaxanthin is widely distributed in the bodies of aquatic animals and in the shells of molluscs (Goodwin, 1984). These animals cannot synthesize astaxanthin themselves, and all the astaxanthin in their bodies comes from food (mainly algae in the water) ). After karrer et al. (1932) first extracted astaxanthin from crab eggs, the by-products of crustacean aquatic products (shrimp, crab) have been the main source of natural astaxanthin. In Norway, astaxanthin is extracted from crushed shrimp shells by acid or enzymatic hydrolysis, followed by extraction with an organic solvent. The yield can reach about 150 mg/kg, and the astaxanthin content of the extracted pigment is over 90%. However, because the pigment content in most shrimp and crab by-products is low, at only 80 to 200 mg/kg, and the extraction costs are high, this method is not suitable for commercial production and has little development potential.

2.1.2 Extraction from algae

Many algae that grow in nitrogen-deficient environments, such as Haematococcus pluvialis, are important astaxanthin-producing bacteria and are considered to have great commercial production prospects. During the cultivation of this algae, if there is a lack of nitrogen sources, astaxanthin can accumulate in the algae, and the astaxanthin content in the dry matter can reach 0.5% to 2.0% (LWoFF et al., 1930), accounting for more than 90% of the total carotenoids.

 In addition, Chlorococcus SP is resistant to high temperatures, extreme pH values, and grows quickly. (LWoFF et al., 1930), accounting for more than 90% of the total carotenoids. In addition, chloroccum SP has the advantages of high temperature tolerance, extreme pH tolerance, fast growth rate and ease of outdoor cultivation. It is considered to be an algae with great potential for large-scale astaxanthin production (Nelis et al., 1991). However, in general, algae have long autotrophic cycles and high requirements for water quality, environment and light, which limits large-scale production. In addition, 87% of the astaxanthin in Haematococcus pluvialis is present in an esterified state, which is poorly absorbed and deposited in some animals (Kvalheim et al., 1985). All of these factors affect the large-scale production of astaxanthin using algae.

2.1.3 Microbial fermentation

Microorganisms known to produce astaxanthin include Mycobacterium lacticola, Brevibacterium 103, and the fungus Pha『『ia rhodozyma. Of these, Mycobacterium lacticola can only produce astaxanthin on hydrocarbon media but not on nutrient agar, while Brevibacterium 103 needs to grow on petroleum. At the end of fermentation, the astaxanthin production is less than 0.03 mg/g, so neither is of practical significance.

Haematococcus pluvialis is considered to be the most valuable microorganism for industrial production of astaxanthin. It was first isolated from the exudate of deciduous trees in the mountainous areas of Alaska, USA, and Hokkaido, Japan, in 1970 (Andrewes et al., 1976), and was later identified as a genus of the fungus Basidiomycota. Haafu yeast is aerobic and can ferment sugars, unlike other yeasts of the same genus. It produces more than 10 kinds of carotenoids, the main ones being astaxanthin, β-carotene, and “-carotene. The astaxanthin content of wild fungi ranges from 40% to 95%. However, the total amount of carotenoids in wild Hanseniaspora yeast generally does not exceed 500 mg/kg of dry yeast, and the yeast cell walls are very thick, so it is difficult for animals to digest and absorb them without breaking the walls.

In order to solve these problems, in recent years, domestic and foreign scholars have conducted in-depth research on the breeding of high-yield astaxanthin strains and the breaking of yeast cell walls, and have achieved gratifying results. For example, using an alcohol waste liquid culture medium to screen for a mutant strain of Rhodotorula glutinis NRRLY-17269, JB2, 2100 to 2270 mg of carotenoids per kilogram of stem cells (Bon et al., 1997). In a study by Calo et al. (1995), a mutant strain of the yeast Phaffia was obtained with an increased astaxanthin content of 23%, reaching 1500 mg/kg of stem cells. Researchers in China have obtained better results by treating the cells with acid heat to break the cell wall, and then extracting the astaxanthin with acetone. Another method is to use enzymes secreted by Bacillus circulams to enzymatically break down the tough cell walls. Overseas, there are already enterprises that use Haver yeast for industrial production of astaxanthin, such as the American Red star company, whose yeast pigment content is 3000-4000 g/t dry yeast; Igene Biotechnology Co., Ltd. has a product with an astaxanthin content of up to 8000 g/t.

2.2 Chemical synthesis

The transformation of β-carotene to astaxanthin requires the addition of two ketone groups and two hydroxyl groups. Chemical synthesis is difficult and most of the astaxanthin produced is in the cis configuration. To date, the only company that has used chemical synthesis to produce astaxanthin on an industrial scale is the Swiss company Hoffmann-La Roche, which markets it under the trade name Carophyll Pink. As astaxanthin produced by fermentation has a lower content, chemically synthesized astaxanthin has a competitive advantage. The synthesis of astaxanthin involves multiple chemical and biocatalytic reactions, with the biocatalytic reaction determining the stereochemistry of the carbon atoms in the intermediates or the position of the substituents on the oxygen atoms. The main precursor for chemical synthesis is (S)-3-acetyl-4-oxo-beta-ionone, which is obtained by asymmetric hydrolysis of (R)-terpene alcohol acetate by different microorganisms, followed by extraction, reflux and then subjected to technical processes such as extraction, reflux.

3. Application effects of astaxanthin

3.1. Coloring effect of astaxanthin

Astaxanthin is the terminal point of carotenoid synthesis. After entering the animal body, it can be stored directly in the tissues without modification or biochemical transformation (Bjorndahl, 1990), giving the skin and muscles of some aquatic animals a healthy and vibrant color, and eggs and poultry appear healthy golden yellow or red. Although β-carotene can be converted into astaxanthin in crustacean aquatic animals, most of it is converted into vitamin A, which has a poor coloring effect, and it does not color common aquatic animals and birds. Only the oxygenated derivatives of carotenoids (xanthophylls) have the ability to color egg yolks (Olson, 1989), and the dihydroxy and diketone carotenoids (astaxanthin) have a stronger coloring effect on egg yolks than the monohydroxy, monoketone or epoxy carotenoids (Braeunlich, 1978).

When Olsen et al. (1994) added astaxanthin to the diet of Arctic char, they found that the redness of the fish was positively correlated with the amount of added astaxanthin, and that a dosage of 70 mg/kg a stable period of pigment formation. Choubert et al. (1996) found that adding 100 mg/kg astaxanthin extracted from yeast to rainbow trout feed increased the carotenoid content of rainbow trout muscle. Kamada et al. (1990) found that adding calendula petal extract containing 0. 1% astaxanthin-containing marigold petal extract in the rainbow trout feed, it was found that not only did the fish's epiboly turn yellow, but the astaxanthin content in the muscles also increased. Li Zhansheng (1993) believes that astaxanthin is the preferred pigment in salmon and rainbow trout feed.

3.2 The role of astaxanthin in enhancing immune function

Astaxanthin is an excellent antioxidant that plays an important role in promoting antibody production, enhancing the immune function of animals, and quenching the production of free radicals. Miki (1991) found that the antioxidant capacity of astaxanthin is 10 times that of β-carotene and 100 times that of vitamin E. These functions of astaxanthin help to improve the survival and health of individual animals. Studies have shown that adding 50 mg/kg astaxanthin to the feed of rock lobsters can significantly improve the survival rate, weight gain and feed conversion rate of the shrimp.

3.3 Astaxanthin's role in promoting growth and reproduction

The eggs of aquatic animals contain high levels of astaxanthin. This high level of astaxanthin can reduce the sensitivity of fish to light and promote the growth and reproduction of fish (Li Shengzhan, 1993). It can also act as a hormone to promote the fertilization of fish eggs, reduce the mortality rate of embryonic development, accelerate individual growth, and increase the speed of maturation and fertility (Torrissen et al., 1994). Astaxanthin can also increase the egg production rate of poultry.

4 Research directions for the application of astaxanthin

Astaxanthin has good application prospects in the aquaculture industry as an excellent feed coloring agent. In recent years, the demand for astaxanthin at home and abroad has been increasing. Each year, 100 tons of astaxanthin are used in rainbow trout farming worldwide, worth 185 million US dollars, and the market potential is considerable.

4.1 Research on astaxanthin production technology

The large-scale production of astaxanthin using Haematococcus pluvialis is the future direction of development. The selection of strains that produce high levels of astaxanthin, the control of optimal fermentation conditions, the improvement of fermentation processes, the use of genetic modification techniques and the selection of inexpensive fermentation raw materials to increase yields and reduce production costs, and the selection of appropriate cell wall-breaking techniques to improve the utilization rate of astaxanthin are all topics that require further research.

4.2 Research into expanding the application of astaxanthin

At present, there is more research into the application of astaxanthin in aquaculture and poultry farming, and there are relatively few reports on its application in livestock farming. How to expand the application of astaxanthin in livestock farming is an area that requires further research. For example, astaxanthin can be used as a feed coloring agent for pigs, taking advantage of its ability to be deposited on the surface of the body and in muscle tissue, so that the skin of the pig is shiny and the muscles are ruddy, improving the quality of the pork. On the other hand, the amount of astaxanthin added to the feed should be systematically studied, and the correlation between the amount added and the coloring effect should be analyzed to determine the appropriate amount of additive in various aquatic products and livestock feeds, so as to achieve the best results with a small investment.

The coloring effect of astaxanthin in feed is related to the feed formula, the health of the animals and the breeding environment. The lipids, antioxidants and vitamin E in the feed can protect the coloring agent from damage and are all conducive to the absorption of astaxanthin by animals. Feed containing a high concentration of calcium and vitamin A, however, can affect the deposition of astaxanthin. In addition, the type of protein in the feed, the oxidation state of the fat, the carotenoid content and the presence of anti-nutritional factors all affect the deposition of astaxanthin in the animal. Studying these influencing factors can better exploit the coloring effect of astaxanthin and reduce its loss in use.

4.3 Research on the safety of astaxanthin

Although there are currently many reports on the effect of astaxanthin added during farming, there are few reports on its residues in animals after use and the toxicity caused by excessive addition. Therefore, research on the safety of long-term use of astaxanthin is also a topic to be explored.