Polysaccharides, also known as polysaccharides, are a class of biomacromolecules that are ubiquitous in biological organisms. They are not only involved in the formation of tissue cytoskeleton, but also an important component of many endogenous bioactive molecules. As a feed additive, polysaccharide has good activity, can improve the body's immunity, and has low toxicity and low drug resistance. It has broad application prospects. Polysaccharides have a certain role in regulating the body's immune function. Its role is multi-pathway, multi-link, multi-target, such as promoting immune cell proliferation and differentiation, secreting various lymphokines, and regulating the neuro-endocrine-immune regulatory network (NIM). Balance and so on. Scholars from various countries have extracted a large number of active polysaccharides from various organisms and found that polysaccharides have a series of effects such as promoting immunity, antibacterial, antiviral, antiparasitic and animal performance.
1 Source of polysaccharides
According to the source, polysaccharides can be divided into plant polysaccharides, microbial polysaccharides and animal polysaccharides. Among the more extensive and in-depth studies are plant polysaccharides and microbial polysaccharides. Plant polysaccharides are derived from the roots, stems, leaves, skin, flowers and seeds of plants. At present, the research is more intensive, such as Astragalus polysaccharide, Angelica polysaccharide, Acanthopanax senticosus polysaccharide, Lycium barbarum polysaccharide, Aloe polysaccharide, Ginseng polysaccharide, Seaweed polysaccharide and so on. Microbial polysaccharides include bacterial polysaccharides and fungal polysaccharides, and hundreds of fungal polysaccharides have been obtained from fungi at home and abroad. Studies on fungal polysaccharides (such as lentinan, ganoderma lucidum polysaccharides, and tremella polysaccharides) are both deep and extensive, and many have been used clinically and have achieved good results. Animal polysaccharides exist in the connective tissue matrix and intercellular substance of animals. The research on animal polysaccharides started late, but it has been paid more and more attention in recent years.
2 effect of polysaccharides
The antiviral activity of the polysaccharide is achieved by interfering with the adsorption of the virus, invading the host cell, inhibiting the activity of the reverse transcriptase, inhibiting the integration of the viral RNA, the reverse transcription process, and improving the immunity of the body.
Chang (1999) and other 0.2% β-1,3-glucan (β-1, 3-glucan) were added to the larvae and adults of P. monodon in feed, and the white spot syndrome virus (White) was used after 15 days. Spot syndome virus), after 20 days of adulthood, was infected with leukoplakia, and the results showed that the survival rate of larvae was 12.2% on the 6th day after challenge, the adult survival rate was 20%, and the control group was 0. After 120 days of poisoning, the survival rate of larvae was 5.5%, and the adult survival rate was 13.3%. The results showed that the addition of dextran can alleviate the white spot syndrome virus of Penaeus monodon. Chang et al. (2003) added 1% of β-1,3-glucan extracted from Schizophyllum to the feed to achieve a survival rate of 42.2% on 12 days after challenge with white spot syndrome virus. % of β-1,3-glucan did not further improve the survival rate after challenge, but decreased to 24.4%. The negative rates of PCR detection of β-1,3-glucan 0.2%, 1%, and 2% were 55%, 65%, and 65%, which means that there were more 0.2% of the added groups in the challenge group. Infected with white spot syndrome virus. Hu Linlin et al. (2008) added chitosan sulfate to feed and fed P. vannamei. The results showed that the addition of chitosan sulfate in the feed was 0.15‰ and 0.50‰, which significantly increased the serum phenol of Penaeus vannamei. Oxidase activity; when added in an amount of 0.15 ,, it can significantly increase the serum superoxide dismutase activity of shrimp; the larvae of the larvae were fed with chitosan sulfate for 4 weeks, and the white spot syndrome virus was infected with the infection. The survival rates of the shrimps in the experimental group were 39.3%, 42.9% and 53.6%, respectively, while the control composition of the untreated chitosan sulfate was only 17.9%. The results showed that the intake of chitosan sulfate significantly improved the ability of L. vannamei to resist white spot syndrome virus infection. Zhang Ming (2008) and other studies on the immune enhancement effect of D-Amino-Oligosaccharide on Chinese shrimp (Penaeus chinensis), the results showed that injection of immunooligosaccharides can significantly enhance the acid phosphatase of Chinese shrimp. Serum immunization indicators such as lysozyme and feeding in the feed can increase the survival rate of the shrimp, and the effect of adding ≥3‰ in the feed is better. Wilaiwan et al. (2004) added 400 mg/kg of fucoidan extracted from lychee, and added the 400 mg/kg fucoidan 5~8 g spot on the 10th day after infection. The survival rate of Shrimp was 46%, the survival rate of P. monodon with the addition of 200 mg/kg fucoidan 12-15 g was 93%, and the survival rate of adding 100 mg/kg fucoidan was 42%.
3 antibacterial and antibacterial effect of polysaccharides
The mechanism of antibacterial action of polysaccharides is multi-faceted. On the one hand, the direct inhibition and detoxification of drugs on bacteria and their toxic products, on the other hand, the main effect is to exert antibacterial and bactericidal effects by regulating the immune defense function of the motives.
Yang Sheng et al (2007) studied the antibacterial activity of water-soluble chitosan against Escherichia coli, Staphylococcus aureus, Proteus, Candida albicans and Pseudomonas aeruginosa using solid medium in vitro bacteriostatic method. The results showed that water soluble Chitosan has an inhibitory effect on Gram-negative bacteria and Gram-positive bacteria, and has a stronger inhibitory effect on Gram-positive bacteria than Gram-negative bacteria. The order of inhibition in the test bacteria is Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, Proteus. Huang et al. (2006) fed Chinese shrimp with 0.5%, 1.0%, and 2.0% polysaccharides from Sargassum fusiforme, and Vibrio harveyi 14 days later, 30 h after injection. Mortality was significantly lower in the % and 1.0% added groups than in the control group, while the 2% added group was not significantly different from the control group. Chi Shuyan et al (2006) added different levels of β-glucan to the feed for 7 days after injection of Aeromonas hydrophila, the survival rate of the control group was only 25%, and the survival of the β-glucan-added group. The rate was 60%-70%, and the 11% β-glucan addition group could significantly increase the activity of ACP and LSZ in the head kidney tissues of Oreochromis. The results showed that the suitable addition amount of β-glucan in the whole male Omni tilapia feed can improve its growth performance and the ability to resist Aeromonas hydrophila infection when the suitable addition amount of β-glucan is 110%～115%. Yan Dawei et al. (2007) added 0% (control), 0.25%, 0.50%, 0.75%, 1.00% chitosan to the basic feed to make 5 test feeds, and 70 days later, the test fish growth rate and Anti-infective ability to Aeromonas hydrophila. The results showed that chitosan had a significant effect on the growth of grass carp and the anti-infective ability of Aeromonas hydrophila (P<0.05). The growth rate and disease resistance of the test fish increased with the addition of chitosan. The trend of increasing first and then decreasing, the 0.50% and 0.75% chitosan group had the highest relative weight gain rate and the strongest anti-infective ability to Aeromonas hydrophila, which was significantly different from the control group, but the two groups were significant. There is no significant difference between them. Chen Yunbo et al (2005) added 0.3%, 0.5%, 1%, 2% chitosan to the basic feed, and fed the gibel carp for 2 months to determine the growth of the fish body and the water-saving gas list of the pathogen. The anti-infective ability (LD50) of cytobacteria showed that the addition of different concentrations of chitosan had a significant effect on the increase of body weight (P<0.05). The addition of different concentrations of chitosan increased the body length of gibel carp. The survival rate had no significant effect (P>0.05). Adding 0.5% and 1% chitosan to the feed could significantly improve the resistance of the gibel carp to Aeromonas hydrophila (P<0.01), adding 0.3%. There was no significant difference between 2% chitosan and control group LD50 (P>0.05). The anti-infective ability was related to the amount of chitosan added. The amount of addition was too large, and the anti-infective ability was weakened. The LD50 of 0.5% and 1% chitosan group was significantly higher than that of 2% chitosan group (P<0.01). Ayyaru et al. (2006) reported that by feeding squid 1% chitosan, lysozyme levels reached the highest after 30 days, which was (4 797±24) IU, while the control group was only (927±75) IU. Chitosan can significantly improve the lysozyme level of the carp; after 45 days, the protection rate was 80% with Aeromonas hydrophila; after 90 days, the challenge was achieved with Aeromonas hydrophila, the protection rate reached 68.9. %. In addition, Rosa sinensis polysaccharide, Astragalus polysaccharide, microalgae polysaccharide, Aster polysaccharide, etc. have also been proved to have strong antibacterial and antibacterial effects.
4 immune promotion of polysaccharides
Polysaccharides can enhance the host's immune system, such as increased antibodies, interferon production and increased lymphocytes.
After Wang Xiaofeng et al (2005) immunized Chinese shrimp with β-glucan and lipopolysaccharide, the total number of Chinese prawns increased by 83.4% and 52.0%, respectively, and the number of small granule cells increased by 100.4% and 67.3%, the number of large granule cells increased by 47% and 10% respectively; meanwhile, the yield of phenol oxidase increased by 81.3% and 104.7%, respectively, but the unit enzyme activity of phenol oxidase did not change significantly before and after stimulation. Transmission electron microscopy (TEM) observation showed that the ultrastructure of Chinese shrimp blood cells changed to varying degrees before and after immune stimulation. Under the stimulation of β-glucan and lipopolysaccharide, the number of rough endoplasmic reticulum (RER) and free ribosomes in small granulosa cells and large granule cells increased significantly, the number of mitochondria increased, and the number of endocrine granules decreased significantly. The ultrastructure of clear cells showed no significant difference except for the increase of RER and mitochondria and the increase of the number of nuclear pore complexes before and after polysaccharide stimulation. Huang et al. (2006) stimulated Chinese shrimp by using Sargasso algae polysaccharide as an immune promoter. The results also showed that seaweed polysaccharide can significantly increase the total number of blood cells, and the appropriate dose can increase the activity of phenol oxidase and lysozyme. Zhang Hongmei et al. (2006) added yeast mannooligosaccharides to Jianye feed. The results showed that the thymus and spleen of the immune organs in the experimental group matured rapidly, and T and B lymphocytes increased, which could produce a large amount of antibodies and improve the immune function of the carp. Xiao Mingsong et al. (2004) found that adding different concentrations of fructooligosaccharides and glycosides in Chinese sturgeon feed can significantly improve the quality of immune organs and immune organ index of Chinese sturgeon, but immunize with Chinese sturgeon at different levels of addition. Organ mass and immune organ index increased to varying degrees. It can be seen that polysaccharides can promote the changes of immune function of aquatic animals and improve their disease resistance. Chang Qing et al. (2006) found that 0.5%, 1% and 2% chitosan were added to the basal diet, and the flower buds (Lateolabrax japonicus) were continuously fed for 60 d to investigate the growth of chitosan on the calyx. The impact of non-specific immunity. The results showed that the addition of 0.5% and 1% chitosan could significantly promote the growth of flower buds, but had no effect on the survival rate. Addition of 0.5% or 1% chitosan at 30 d can effectively increase the complement activity, lysozyme activity and phagocytic activity of the flower bud; at 60 d, only the complement activity was significantly increased. The addition of chitosan has no effect on the number of white blood cells. Wang Shuqin et al. (2004) also reported that chitosan can promote phagocytic activity, true respiratory burst and phagocytic phagocytic activity of gibel carp. Using chitosan as a feed additive, five groups (0%, 0.3%, 0.5%, 1.0%, 2.0%) were used to carry out different feeding experiments on cage cultured allogyogenetics silver crucian carp. After 2 months of feeding, the lysozyme activity and leukocyte phagocytic activity of the spleen spleen serum and spleen and head kidney supernatant were extracted from each group. The experimental results showed that the addition of 0.5% or 1.0% chitosan was effective. To improve the lysozyme activity of the gibel carp (P<0.01) and the phagocytosis of leukocytes (P<0.01), the chitosan can be used as an immunopotentiator for aquatic animals, and the suitable addition amount in the feed is 0.5%. .
The application of polysaccharides in anti-parasitic research is rarely reported, but seaweed polysaccharides, astragalus polysaccharides, fungal polysaccharides and the like are considered to have antiparasitic activity.
5 Summary
At present, the mechanism of action on polysaccharides against viral and bacterial diseases is still not fully understood. Most studies still remain on the immune index after addition and the survival rate after infection. The biological activity of polysaccharides is closely related to its structure, but its structure is still relatively rare, and the mechanism of its physiological activity is still not clear, and these are still to be further studied. As a feed additive, polysaccharide has the advantages of safety, non-toxicity and stability, so it has a good application prospect in aquaculture.
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