What Are the Uses of Astaxanthin in Hindi?

Astaxanthin is widely found in crustaceans, algae and other marine organisms and microorganisms. It is a type of red carotenoid[1-3] that has the effect of boosting the immunity of aquatic animals, resisting oxidation, increasing production and replacing antibiotics[4-5]. Aquatic animals cannot synthesize astaxanthin on their own and must obtain it by eating algae in the water. In aquaculture, astaxanthin is usually supplemented to animals through feed. Astaxanthin is divided into natural extraction and artificial synthesis. Natural astaxanthin extraction includes extraction from crustacean waste, the red fife yeast method, and the cultivation of Haematococcus pluvialis [6]. Crustacean waste extraction has a wide range of raw materials, but the extraction process is prone to spoilage and produces toxic substances [7].

The red yeast fermentation method is fast, but it is difficult to apply on a large scale due to technical problems. The algal extraction method is currently the most ideal way to obtain natural astaxanthin, and the astaxanthin produced is of the best quality, but it is extremely difficult to obtain. At present, most astaxanthin on the market is synthetic [8], and the Swiss company Hoffmann-La Roche has produced 5% to 10% all-trans astaxanthin [9]. Experiments on astaxanthin deposition in rainbow trout have shown that natural astaxanthin has better deposition properties than synthetic astaxanthin [10]. This paper discusses the physical and chemical properties of astaxanthin and its application in aquaculture, with the aim of providing a reference for the application of astaxanthin under the new era of green and healthy aquaculture.

1. Physicochemical properties of astaxanthin

Carotenoids are a group of more than 700 organic fat-soluble pigments [11]. Different carotenoids are closely related [12] and can usually coexist or transform into each other. Astaxanthin is a carotenoid with the molecular formula C40H32O40, melting point 215 °C, boiling point 773 °C, and density 1.071 g/mL[13]. Astaxanthin is highly soluble in organic solvents, with solubilities of 10.0, 0.2, 30.0, and 0.5 g/L in chloroform, acetone, dichloromethane, and dimethyl sulfoxide, respectively.

Astaxanthin has a six-membered α-hydroxy-cyclopentadione ring structure at each end, with four conjugated double bonds made up of isoprene units in the middle. C-3 and C-3' have chiral centers. Because two conformations can form a chiral center, astaxanthin with two chiral carbon atoms C-3 and C-3' can exist in the R or S form, forming three isomers: (3S,33'), (3R,3R') and (3R , 3S' ), of which the enantiomers (3S, 3S') and (3R, 3R') exist in pairs and have opposite optical activity, causing plane polarization to rotate to the left or right, while (3R, 3S') has no optical activity [13]. Astaxanthin exists in nature in both esterified and free forms. Most of the free form is synthetic astaxanthin (3S, 3R'), while natural astaxanthin is generally the esterified isomer (3R, 3R') and (3S, 3 S') is the main astaxanthin product of Rhodopseudomonas palustris, while Haematococcus pluvialis mainly produces astaxanthin with a single trans (3S, 3S') ester [14].

There are some disadvantages to the application of astaxanthin in animal production: (1) Hydrophobicity. Astaxanthin is a lipophilic substance that is extremely difficult to dissolve in non-polar solvents. The two hydroxyl groups at each end can interact with fatty acids to esterify astaxanthin, which is more hydrophobic than free astaxanthin [15]. (2) Instability. Astaxanthin is extremely unstable due to its unique unsaturated conjugated double bond structure. When exposed to light, oxygen, and temperature changes, astaxanthin is very prone to lose activity, fade, and degrade during processing and storage, affecting the quality and color of the final product. Studies have shown that astaxanthin in the skin and shells of aquatic animals is mostly in an esterified form, while astaxanthin in the body is distributed in the heart and muscles in a free state [16]. For example, the astaxanthin in salmon meat is in a free state, but the free astaxanthin is extremely unstable and easily oxidized.

2 Biological functions of astaxanthin

Astaxanthin is a natural antioxidant that is 500 times more effective than other carotenoids and vitamin E at scavenging free radicals. Astaxanthin has biological functions such as anti-diabetes, reducing oxidative damage, strengthening the immune system, improving athletic performance, preventing cardiovascular and cerebrovascular diseases, anti-tumor and anti-inflammatory activities [17].

2.1 Anti-inflammatory

Inflammation is a defence response of the body to external stimuli. Within certain limits, it is beneficial to the body, but when inflammation is uncontrollable, it can cause significant damage to the body [18]. Astaxanthin has a significant effect on chronic inflammation, inflammation caused by gingival keratinocytes, dermatitis and other inflammations [19]. The mechanism of action of astaxanthin in the body is to inhibit the expression of pro-inflammatory factor-related genes and reduce enzyme activity in the signal pathway of the inflammatory response.

2.2 Anti-tumor

Natural carotenoids have a certain effect in terms of anti-cancer [20]. The peroxidation of proteins and fats is the direct cause of cell senescence and degeneration, and can even further worsen cancer. The antioxidant effect of astaxanthin can inhibit peroxidation and reduce the possibility of cancer. Zhang et al. [21] found that natural astaxanthin can inhibit the proliferation of K562 leukemia cells and induce apoptosis. Abnormal communication between cells can lead to tumorigenesis and metastasis. Astaxanthin can promote cell-to-cell communication and upregulate the expression of communication protein genes [22].

2.3 Improves immunity

Polyunsaturated fatty acids, which are abundant in cell membranes, are highly susceptible to free radical attack. Natural astaxanthin can scavenge these free radicals and enhance immunity by protecting the immune system. Natural astaxanthin extracted from Haematococcus pluvialis can enhance monocyte-macrophage function [23], while rapidly increasing plasma immunoglobulin G (IgG) and immunoglobulin M (IgM) levels, and the activity of natural killer cells is also increased, thereby enhancing the body's immunity [24].

3 Astaxanthin in aquaculture

Astaxanthin has a wide range of applications in aquaculture and is of great significance in promoting the growth and breeding of aquatic animals, coloring and improving survival rates. Astaxanthin has antioxidant, anti-stress, coloring, gonad development-promoting, immune-enhancing and anti-inflammatory effects. At present, astaxanthin is widely used in the large-scale farming of shrimp, crabs, trout, etc., and has been defined by food safety monitoring agencies in many countries as an efficient and safe feed additive [25].

3.1 Coloring effect

The coloring of crustaceans is inseparable from astaxanthin, but crustaceans themselves cannot synthesize astaxanthin from scratch [26]. Crustaceans exhibit different colors, which are due to the combination of proteins and astaxanthin into complexes. Wu Renfu et al. [27] found that with the correct feeding method and feeding ratio, the addition of 26.27 mg/kg astaxanthin to the feed can significantly increase the total carotenoid content in the tissues of female river crabs compared to no addition, indicating that astaxanthin has the effect of improving the color of river crabs. As a feed additive, the deposition rate of astaxanthin in the shells and flesh of shrimp increased by 75.5% and 66.4%, respectively.

The deposition of astaxanthin in the shell and meat of the shrimp makes the shrimp and its meat more shiny [28]. Astaxanthin is also widely used in ornamental fish farming. For example, adding astaxanthin to rainbow trout feed can significantly improve muscle color [29] and the total amount of carotenoids deposited in the body [30]. The redness value is an important indicator for the culture of the spotted cichlid. Adding astaxanthin to the feed can effectively increase its redness value [31]. Jiang Jufeng et al. [31] found that the body color of the spotted cichlid gradually increased after the 4th week when natural astaxanthin was added to the feed, and the body color became significantly brighter at the 8th week. The best color enhancement effect was achieved with an addition of 150 mg/kg.

Wang Xin et al. [32] found that when the astaxanthin dosage was 100–250 mg/kg, the carotenoid content and caudal fin chroma value of tissues such as the eyes, fins, skin and muscles of the high-body crucian carp were significantly increased; when the astaxanthin dosage was 200 mg/kg, the carotenoid content of the eyes and fins was the highest; when the astaxanthin dosage was 250 mg/kg, the carotenoid content of the skin and muscles of the high-body crucian carp was the highest. Generally, the pigment composition of the feed for river crab farming is unstable and there are few types. Adding astaxanthin can compensate for the lack of pigments to a certain extent, but astaxanthin is expensive. The feed ratio and process should be improved to control costs and increase the deposition rate of astaxanthin in animals. Astaxanthin is a fat-soluble carotenoid, and the addition of phospholipids to the feed is beneficial for the digestion and absorption of astaxanthin in the body and its deposition in the liver and pancreas [33].

3.2 Promoting the development of crustacean gonads

Adding astaxanthin to feed can protect the development of the ovaries of parent shrimp and improve reproductive capacity. The content of astaxanthin in shrimp affects the quality of the larvae in the embryo, and a shortage of astaxanthin can lead to a reduction in the quality of the larvae [34]. Astaxanthin can enter the nucleus as an active substance and be received by hormone receptors as a precursor, activating hormones and promoting the accelerated development of oocytes [35]. The swimming crab is a major aquatic species in China that is cultivated in large quantities along the coast of Guangdong, but due to the limitations of pond farming conditions, the ovarian development of female crabs and the color of their shells are inferior to those of natural swimming crabs [36]. Adding astaxanthin to the feed can increase the redness of the cooked crab and the size of the ovaries, effectively improving its quality and price in the market.

Ma Nan et al. [37] found that adding different amounts of synthetic astaxanthin to the feed and feeding it for 30 days did not significantly affect the gonadosomatic index (GSI) and hepatopancreatic index (HSI) of female crabs. The GSI of crabs in each group was 3.64% to 4 .27%, and the HSI was 10.25%~11.16%; after 60 days of feeding, the GSI increased significantly to 8.25%~8.63%, and the HSI decreased to 8.00%~8.85%. These results differ from those of Guo Chunyu [38]. The reason for this may be that Ma Nan et al. [37] used mature female crabs weighing about 90 g, while Guo Chunyu [38] used blue crabs weighing about 27 g. Astaxanthin can promote shell shedding and thus gonad development. Ma Nan et al. [37] used a variety of astaxanthin isomers, of which all-trans astaxanthin only accounted for 25%. Guo Chunyu [38] extracted natural astaxanthin from Haematococcus pluvialis powder, which is mainly all-trans-astaxanthin. The effect of the two on gonad development is not yet clear. During oocyte development, astaxanthin accumulates with yolk protein and eventually becomes an important component of yolk protein.

3.3 Improves growth and reproductive performance

The addition of astaxanthin to feed can improve the growth and reproductive performance of aquatic animals. Jiang et al. [39] found that 60 mg/kg of microalgal astaxanthin can effectively improve the growth performance and survival rate of river crabs, and also has a significant effect in terms of antioxidant and ammonia nitrogen stress. Guo Chunyu [38] found that the addition of 80 mg/kg of Haematococcus pluvialis soaps as a feed additive for river crabs had the greatest effect on the weight gain and survival rate of juvenile river crabs.

Liu Xiaohui[40] found that continuous feeding of shrimp with a diet supplemented with Haematococcus pluvialis for 35 days increased the average weight and length of the shrimp, and that the natural astaxanthin produced by Haematococcus pluvialis had a better growth-promoting effect than synthetic astaxanthin. Ju et al.[41] found that Haematococcus pluvialis was fed to shrimp as a feed additive instead of protein raw materials for 56 days, and the shrimp's feed coefficient was significantly reduced and the growth rate significantly increased. Wang et al. [42] found that the addition of astaxanthin to the feed promoted a significant increase in the metabolic amount of pyruvate in the bodies of white leg shrimp, and the expression of pathway genes related to glycolysis/glycolysis increased significantly.

3.4 Strengthening immune function

Astaxanthin is a non-nutrient additive that can reduce the toxicity of some cytokines in the non-specific immune response and increase the activity of complement and lysozyme [31]. Astaxanthin has a significant effect on the prevention and control of fish, shrimp and crustacean diseases, and can improve the immunity, survival rate and reproductive rate of farmed animals, and has a positive effect on the normal growth and health of aquatic animals [43]. In general, damage to the body caused by free radicals is repaired by the body's total antioxidant defence system. Free radicals are constantly produced and constantly removed in the body of animals under normal physiological conditions to achieve a dynamic balance.

The stress caused by oxidation can be alleviated by astaxanthin activating the Nrf2/Keap1 pathway[44]. The total antioxidant defense system is composed of enzymatic systems such as superoxide dismutase and catalase, as well as non-enzymatic reactions involving astaxanthin, vitamins, amino acids, etc. First, as part of the non-enzymatic defense system, astaxanthin's unique long-unsaturated and conjugated system of outer unstable electron orbits can quickly remove free radicals in cells and protect the body from damage. Second, astaxanthin can reduce cell membrane permeability, reduce the entry of ascorbate, hydrogen peroxide and other substances produced during fat oxidation into the lipid body, and also remove the negative effects caused by the oxidation of hydroxyl radicals, thereby protecting the phospholipid [38] and enhance immunity.

Ma et al. [45] found that adding astaxanthin to the diet can significantly increase the serum superoxide dismutase and catalase activities of the abalone Haliotis rugosa and reduce the propylene glycol content. The higher the superoxide dismutase and catalase activities, the stronger the body's ability to compensate for free radicals and the stronger the antioxidant capacity.

Yu et al. [46] found that astaxanthin can reduce damage to the liver and pancreas and protect the liver of white shrimp. Zhou Yifan et al. [47] found that compared with the control group and other added amount groups, the gene expression in the group with a daily diet of 50 mg/kg astaxanthin was significantly higher. In addition, the total antioxidant capacity, specific growth rate and weight gain rate of crayfish were significantly improved by adding 50 mg/kg astaxanthin and 100 mg/kg tea tree oil to the diet. Xu Changfeng et al. [48] found that the addition of astaxanthin can effectively improve the antioxidant and immune capacity of sea bass. The serum lysozyme activity of sea bass in the 150 mg/kg group was significantly higher than that of the control group, and the serum complement C3 content of sea bass in each astaxanthin group was significantly higher than that of the control group.

The onset of disease in river crabs is related to many factors, such as the water environment, pathogens and the crabs' own immunity. Fungi, parasites, microorganisms, bacteria and viruses are the main culprits that cause damage and death in river crabs, and stress changes in the water environment can also lead to disease in river crabs. Ma Wenyuan et al. [49] found that astaxanthin can improve the immunity of river crabs and enhance their disease resistance to Aeromonas hydrophila. Astaxanthin and vitamin C added together in the feed can be used to prevent Vibrio harveyi. Astaxanthin is also very effective in combating inflammation [50]. Astaxanthin has a very significant inhibitory effect on the cytokines that induce inflammation, and is very effective in combating diseases such as enteritis. In addition, astaxanthin can promote the development of the gonads of crustaceans and improve reproductive performance.

4 Outlook

Astaxanthin is widely used in aquaculture due to its unique functions. However, there is currently little research on the immune protection and effects on ovarian development of astaxanthin, and there is also little research on the mechanism of the antioxidant effect of astaxanthin. Since astaxanthin is easily affected by light and oxygen content, improper feed processing and transportation methods can reduce the effect of astaxanthin. Therefore, the feed processing technology should be improved, packaging materials with better airtightness should be selected, and the process from processing to feeding should be completed within 30 days at best to maximize the utilization of astaxanthin.

In addition, the source and purity of astaxanthin in different studies can lead to differences in test results. Further research is needed on the optimal dosage, method of addition and mechanism of action of astaxanthin, as well as comprehensive research on the optimal dosage of astaxanthin according to different breeding species, stages and environments, to provide a reference for the application of astaxanthin in the green and healthy breeding of aquatic organisms.

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