Currently, colorants added in culture mainly include natural colorants and chemically synthesized carotenoids. Natural colorants refer to extracts of animals, plants, and microorganisms rich in carotenoids and lutein. Chemically synthesized carotenoids include carotenes and lutein. Astaxanthin can be naturally extracted or chemically synthesized. It is an oxygenated derivative of carotene and has become one of the most widely used forage colorants in culture. Now the structure of astaxanthin. The nature, production methods, application effects in aquaculture and their development prospects are elaborated.
1 Structure and physicochemical properties of
Astaxanthin, also known as astaxanthin, is chemically known as 3,3'-dihydroxy- 4,4'-dione-beta-, beta'-carotene. Its molecular formula is C40H52O4, which is a ketone. Carotenoids contain two hydroxyl groups (-OH) and two keto groups (=O), the majority of which are naturally present in the form of esters.
Shrimp is an oxygen-containing organic compound with a color that is pink, insoluble in water, and soluble in most organic solvents, in acid. It is unstable under oxygen, high temperature and ultraviolet light conditions, and is easily oxidized and degraded.
2 Astaxanthin production method
There are two main methods for the production of astaxanthin, natural extraction and chemical synthesis.
2. l Natural extraction of astaxanthin Natural astaxanthin is often found in certain animals, algae and micro-organisms. Its production can be divided into extraction from animals and their by-products, extraction from algae and microbial fermentation.
2.1. l Astaxanthin extracted from animals and their by-products is distributed in the body of aquatic animals and in the shells of mollusks (GOOd-win, 1984). These animals cannot synthesize astaxanthin itself, and all the astaxanthin in the body is derived from Food (mainly algae in water). Karrer et al. (1932), the first product of the crustacean aquatic product (shrimp and crab), has been the main raw material for the extraction of natural shrimp fertility. In Norway, after the shrimp shell is crushed, it is hydrolyzed by acid or enzymatic method, and finally extracted with organic solvent to extract shrimp fertility, the yield is up to 150 mg/kg, and the astaxanthin in the extracted pigment accounts for 90%. the above. However, because most of the shrimp and by-products have low pigment content, only 80-200 mg/kg, and the extraction cost is high, this method is not suitable for commercial production, and the development potential is not great.
2. l. 2 Extracting many algae from algae in a nitrogen-deficient environment, such as Haenaococus pluvialis, is an important astaxanthin-producing bacterium and is considered to be a commercially promising algae. When the algae is lacking in the culture process, the astaxanthin can be accumulated in the algae, and the astaxanthin content in the sub-substance can reach 0.5%-2.0% (LWOff et al., 1930). It accounts for more than 90% of the total carotenoids. In addition, ChlO. urnSP has the advantages of high temperature resistance, extreme pH resistance, fast growth rate and easy outdoor culture. It is considered to be a promising algae for large-scale production of astaxanthin (Nelis et al., 1991). However, in general, algae have a long autotrophic cycle, high requirements for water quality, environment and light, and large-scale production is limited. In addition, 87% of shrimps in Haematococcus pluvialis exist in an esterified state, and absorption and deposition in some animals are poor (Kvalheim et al., 1985). These affect the use of algae for astaxanthin. Large-scale production.
2.1.3 Microbial Fermentation Microorganisms known to produce shrimp fertility are Myobacterium lerticola, Brmibacterium, and Phaffia rhozyma of the fungus Basidiomycetes. Among them, Mycobacterium lacticum can only produce shrimp fertility on hydrocarbon medium, but not on nutrient agar, while Brevibacterium 103 is grown on oil, and the yield of shrimp is not more than 0.03 mg/g at the end of fermentation. The practical application is of little significance. Is the most valuable microbe for the industrial production of shrimp fertility. It was originally isolated from deciduous tree exudates from the mountains of Alaska in the United States and Hokkaido in Japan in 1970 (Andrewes et al., 1976). It was identified as a genus of the fungus Basidiomycetes. The yeast has different aerobic properties from other yeasts of the same genus and is capable of fermenting sugars. Among the more than 10 carotenoids produced by it, there are mainly shrimp, beta-carrot, gamma-carotene, etc. Shrimp fertility accounts for 40% to 95%. However, the total amount of carotenoids in wild-type yeast is generally not more than 500 mg/kg dry yeast, and the yeast cell wall is very thick, and it is difficult to be digested and absorbed by animals without breaking the wall. In order to solve these problems, in recent years, domestic and foreign scholars have conducted in-depth research on the breeding of high-yield shrimp fertility strains and the breaking of yeast cells, and have achieved gratifying results. If the mutant strain JB 2 of the yeast F. cerevisiae NRRLY-17269 was screened using the alcohol waste medium, 2100-2270 mg of carotenoid per kilogram of stem cells was obtained in the 5 L fermenter test (Bon et al., 1997). The astaxanthin content of the mutant strain of the yeast obtained by Calo et al. (1995) increased by 23% to 1500 mg/kg stem cells. Chinese researchers used acid heat-treated cells to break the wall, and then extracted astaxanthin with acetone to obtain better results. Enzymatic hydrolysis of tough cell walls by enzymes secreted by BaCillus circula is also a method of breaking the wall. In foreign countries, companies that use industrial yeast to produce astaxanthin, such as Red Star Company of the United States, have a yeast pigment content of 3000-4000 g/t dry yeast; lgene Bios Co., Ltd. has astaxanthin content of up to 8000 g/ t.
2.2 Chemical Synthesis
The conversion of β-carotene to astaxanthin requires the addition of two ketone groups and two hydroxyl groups. Chemical synthesis is difficult, and most of them are cis structures. So far, the chemical synthesis method for industrial production of shrimp fertility is only the Swiss company Hofflnann-In-ROche, which is sold under the trade name Carophyll pink, with an astaxanthin content of 5% to 10%. Chemically synthesized astaxanthin has a certain competitive advantage due to the low content of shrimp fertilization produced by fermentation. The synthesis of astaxanthin needs to be completed by a multi-step chemical and biocatalytic reaction. The role of biocatalysis is to determine the stereo configuration of the intermediate carbon atom or the substitution position of the oxygen atom in the synthesis process. The main precursor of chemical synthesis is (S)-3-acetic acid-4-oxo-β-ionone, which is asymmetrically hydrolyzed by (R)-nonenol acetate by different microorganisms. The resulting product is treated by extraction, reflux distribution and recrystallization. The precursor material is converted into fifteen-carbon Wittig salt by reaction, and finally two fifteen-carbon Wittig salts are the same + carbon. The dialdehyde reaction produces astaxanthin (Widmer et al., 1989).
3 Application effect of
3.1 Coloration of astaxanthin Astaxanthin is the end point of carotenoid synthesis. It can be stored directly in tissues without modification or biochemical conversion after entering the animal body (Bjomdahl, 1990), making the skin of some aquatic animals Healthy and bright colors appear in the muscles, giving the eggs, birds, feathers, skin, feet, and eyes a healthy golden or red color. Although β-carotene can be converted into astaxanthin in crustacean aquatic animals, most of it is converted to vitamin A, which has a poor coloring effect, and it cannot be colored in ordinary aquatic animals and poultry. Only the oxygenated derivatives of carotene (lutein) have the function of coloring egg yolk (Olson, 1989), and the dihydroxy and diketo carotenoids (astaxanthin) are more monohydroxy- and monoketo-based. Or epoxy carotenoids have a strong coloring function on egg yolk (Braeunlich, 1978).
Olsen et al. (1994) added astaxanthin to the Arctic red-pointed frog feed and found that the redness of the Arctic red-pointed salmon meat was positively correlated with the amount of astaxanthin added, and the pigmentation was achieved when the amount was 70 mg/kg. stable period. Choubert et al. (1996) added 100 mg/kg of astaxanthin extracted from yeast to rainbow trout feed and found that the carotenoid content in rainbow trout muscle increased. Buddhism et al. (1990) added 0% to the rainbow trout feed. L% astaxanthin's calendula petal extract found that not only the fish's epidermal Phosphorus turned yellow, but also the content of shrimp fertility in the muscle increased. Li Zhansheng (1993) believes that astaxanthin is the preferred pigment in the feed of salmon and rainbow trout.
3.2 Astaxanthin enhances immune function Astaxanthin is an excellent antioxidant that plays an important role in promoting antibody production, enhancing immune function, anti-oxidation and quenching free radicals. Miki (1991) found that astaxanthin has 10 times more antioxidant capacity than beta-carotene and 100 times higher than vitamin E. These functions of astaxanthin contribute to the survival and health of individual animals. Studies have shown that the addition of 50 mg/kg of shrimp fertility to the unicorn shrimp feed can significantly improve shrimp survival, weight gain and feed conversion.
3.3 Astaxanthin promotes growth and reproduction The content of shrimp fertility in aquatic eggs is high. This high content of shrimp can weaken the sensitivity of fish to light and promote the growth and reproduction of fish. , 1993), it acts as a hormone to promote fertilization of fish eggs, reduce the mortality of embryonic development, accelerate individual growth, increase maturity and fertility (Torrissen et al., 1994). Astaxanthin can also increase the egg production rate of poultry.
4 Research direction of application
As an excellent feed coloring agent, astaxanthin has a good application prospect in the breeding industry. In recent years, the demand for astaxanthin has been increasing at home and abroad. The annual consumption of astaxanthin for rainbow trout farming in the world is 100 tons, worth 185 million US dollars, and the market potential is considerable.
4. l Research on astaxanthin production technology The large-scale production of shrimp fertility by using yeast fermentation is the future development direction. Screening strains with high astaxanthin production, controlling the optimal conditions for fermentation, improving fermentation process, using genetic improvement techniques and selection Cheap fermentation raw materials to increase production and reduce production costs, and the selection of appropriate wall breaking technology to improve the utilization rate of shrimp fertility is a subject to be further studied.
4.2 Expanding the application of astaxanthin At present, there are many studies on the application of shrimp fertility in aquaculture and poultry farming, and reports on the application of livestock breeding are rare. How to expand the application of astaxanthin in livestock is the direction that needs further research in the future, such as the use of astaxanthin in the surface and muscle tissue deposition characteristics as a feed coloring agent for pigs, so that the pig's skin color brightens Muscle is rosy to improve the quality of pork. On the other hand, the amount of astaxanthin added to the feed should be systematically studied, and the correlation between the added amount and the coloring effect should be analyzed to determine the appropriate amount of astaxanthin in various aquatic products and livestock feeds. Invest in to produce the best results. The coloring effect of astaxanthin in the feed is related to the formulation of the feed, the health of the animal and the environment of the culture. The oil, antioxidants and vitamin E in the feed can protect the colorant from damage and are beneficial to the animal. The absorption of the pigment, while the feed containing higher concentrations of calcium and vitamin A will affect the deposition of astaxanthin. In addition, the type of protein in the feed, the oxidation state of fat, the carotenoid content and the presence of anti-nutritional factors all affect the deposition of astaxanthin in animals. Studying these influencing factors can better exert the astaxanthin coloring effect and reduce its loss in use.
4.3 Study on the safety of astaxanthin Although there are many reports on the effect of astaxanthin in the cultivation, there is little report on the toxicity caused by the residue and excessive addition in the animal after use. Therefore, the shrimp is used for a long time. The safety research of chlorophyll is also a subject to be explored.
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