| As the expanding of human being`s activities and the growing of industrial and agricultural production, heavy metal pollution has become a focus around the world, particularly in Coastal and Estuary region. Cadmium (Cd) is considered to be one of the most toxic heavy metal. Marine shellfish culture is the pillar industry in China`s aquaculture industry, and Oyster is considered to be the most economic valued kind, but shellfish mostly lives at coast in a fixed manner, which makes it has a strong ability to accumulate heavy metals and can`t exclude by itself, so finally the enriched heavy metals will pass to human beings through the food chain, which would thread to human health. Therefore, shellfish contamination of heavy metals, especially Cd pollution has become a major issue of food safety.Chitosan oligosaccharide (COS) has a good water solubility, and contain a large number of hydroxyl (-OH), amino (-NH2) or acetylamino (-NHCOCH3), which could be a good ligand of metals. So this article based on the previous research, discuss the preparation of the COS and metal complexes, and use UV-visible and IR spectrum to characterize its configuration. The results showed that: the degree of deacetylation (D.D.) and molecular weight (Mr) of COS have significant impact on its absorb ability to metals, when D.D. is 90% and Mr is 2000Da, the content of magnesium in complex can be up to 1349mg/Kg; Spectrum characterization indicated that the complex mainly form its coordination bond with N on amino and O on hydroxyl. After 3 days of Cd exposure concentration of 50μg/L, the Pacific oyster was treated with the complex, it was found that the complex has removal effect on Cd residual in oyster, and metal type, D.D. and Mr of COS all have significant impact on its Cd removal ability. When D.D. and Mr of COS is 90%, 2000Da respectively, its complex with magnesium ion can remove Cd residue from oyster, and the removal rate can reach 34.68% compared to blank after 2 days deal with the complex concentration of 100mg/L, while the content of protein, sugar, fats, and moisture content and other beneficial metal elements didn`t change significantly.Carboxymethyl chitosan oligosaccharide (CM-COS) is the production of carboxymethylation to COS, on whose structure to introduce carboxymethyl (-CH2COOH), and the introduction of carboxymethyl (-CH2COOH) enhanced its ability to combine metal ions. This paper investigates the preparation conditions of CM-COS and researches the coordination conditions of CM-COS to magnesium ion, and CM-COS and its magnesium complexes were characterized by UV-visible and IR spectrum. The results showed that: the mass concentration and addition of NaOH, the addition of chloroacetic acid (CA) all has significant impact on substitute degree (D.S.) of CM-COS. When NaOH`s mass concentration is 30%, and mass ratio of NaOH and COS is 5:1, and molar ratio of CA with chitosan oligosaccharide units (ie, glucosamine) is 1:1, the D.S. of production is the highest, up to 1.38; Temperature, pH, D.S. has a significant impact on the adsorption of magnesium ion, and the influence order were D.S.> pH> temperature> addition of magnesium ion. The higher the degree of substitution, the maximum the adsorption capacity to magnesium, the higher the pH, the stronger the adsorption capacity, and the adsorption is exothermic, the lower the temperature, the stronger the adsorption capacity, magnesium addition on the adsorption was not significant. Optimum adsorption conditions is the temperature of system reaction 30℃, pH 9, D.S. 0.92, molar ratio of magnesium ion and sugar is 0.5. Spectrum characterization showed that CM-COS mainly use O and N on carboxymethyl (-CH2COOH) and amino (-NH2) to form coordination bond. CM-COS would be applied to Pacific oyster which were treated with Cd exposure concentration of 20μg/L for 3 days, and result showed that the agent can remove the Cd residual from oyster significantly vs blank. D.S. and molecular weight are major factors in the removal of Cd. When the molecular weight and D.S. of CM-COS was 2000Da, 0.68 respective, the removal rate of Cd up to 41.90% compared with the blank with the removal concentration is 50mg /L last for 3 days. Cd mainly remove from oyster`s digestive gland. There was no effect on oyster nutrition content by the removal agent, and on other beneficial metals have a certain influence, but compared with the blank there was no significant difference.At present, there are two purification methods to improve the quality of shellfish, including net water temporary rearing and purification factory, which can only remove pathogenic microorganism, and have little or no effect to remove petroleum hydrocarbon, heavy metals, pesticide or marine toxins from shellfishes. This paper aims to develop a removal agent which can effectively remove Cd in the process of removing of pathogenic microorganisms at the same time, providing guarantee for the aquatic product safety and human health. |
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