Study Of Heavy Metal Adsorbent And Its Application In Oyster Sauce

Heavy metal ions do great harm to the human health. As our country's industrialization process, these harmful heavy metal ions enter the environment by many ways, and pose a great security risk to waters and foods,especially the seafoods. And then these affect the security of seafood seasonings a lot. Therefore, the removing of heavy metal ions is imminent. And research of this paper can provide technical support and theoretical reference on the removing of heavy metal ions from waters and seafood seasonings.In this paper, immobilizing of metallothionein(MT) and the ability of immobilized MT in removing heavy metal ions in solution are studied. Immobilizing of 2-mercaptonicotinic acid and the ability of immobilized 2-mercaptonicotinic acid in removing heavy metal ions in solution are investigated. And using of chitosan-sodium alginate-MT gel balls in removing Pb²⁺ from oyster sance is also analyzed.MT is immobilized by polyacrylonitrile (PAN) membrane. The immobilization conditions and the characterizations of the immobilized MT are investigated. The results show that the optimal conditions of immobilizing are hydrolysis temperature 50℃,hydrolysis time 10min,NaOH 1.0%,activation reagent (EDC) 0.015mol/L,MT 8mg/mL. The content of immobilized MT is 7.86μg/cm². And the removal rates of the immobilized MT to Cd²⁺,Pb²⁺,Cu²⁺ in solution are up to 80%,75%,81%, respectively. By using of 0.1 mol/L HCl as desorption agent, the PAN-MT membrane which saturated adsorption can be utilized after regeneration. After dealed by three times, the removal rates of PAN-MT membrane to Cd²⁺,Pb²⁺,Cu²⁺ are up to about 65%.In addition, MT is also immobilized by sodium alginate double coacervation method. The immobilization conditions and the characterizations of the immobilized MT are investigated. The results show that the optimal conditions of immobilizing are chitosan 0.4%,sodium alginate 1.5%,CaCl₂ 1.0%,MT 8mg/mL. The recycling rate of immobilized MT is 84%. And the removal rates of the immobilized MT to Cd²⁺,Pb²⁺,Cu²⁺ in solution are up to 75%,96%,80%, respectively. The adsorbing equilibriums are reached after about 2h. By using of 1.0 mol/L HCl as desorption agent, the chitosan-sodium alginate-MT gel balls which saturated adsorption can be utilized after regeneration. After dealed by three times, the removal rates of chitosan-sodium alginate-MT gel balls to Cd²⁺,Pb²⁺,Cu²⁺ are up to about 55%.2-mercaptonicotinic acid is immobilized by polyacrylonitrile (PAN) membrane. The immobilization conditions and the characterizations of the immobilized 2-mercaptonicotinic acid are investigated. The results show that the optimal conditions of immobilizing are hydrolysis temperature 50℃,hydrolysis time 10 min,NaOH 1.0%,1,6-Hexylenediamime(HMDA) 5.0%,2-mercaptonicotinic acid 10mg/mL. The content of immobilized 2-mercaptonicotinic acid is 7.46ng/cm²,and the content of sulfhydryl on the membrane surface is 35nmol/cm². And the removal rates of the immobilized 2-mercaptonicotinic acid to Cd²⁺,Pb²⁺,Cu²⁺ in solution are up to 84%,88%,81%, respectively. By using of 0.1 mol/L HCl as desorption agent, the PAN-mercaptonicotinic acid membrane which saturated adsorption can be utilized after regeneration. After dealed by three times, the removal rates of PAN- mercaptonicotinic acid membrane to Cd²⁺,Pb²⁺,Cu²⁺ are up to 77.3%,79.1%,69.9%, respectivly. It shows the PAN- mercaptonicotinic acid membrane can be reused for many times.Moreover, 2-mercaptonicotinic acid is also immobilized by sodium alginate double coacervation method. The immobilization conditions and the characterizations of the immobilized 2-mercaptonicotinic acid are investigated. The results show that the optimal conditions of immobilizing are 0.4% chitosan,2.0% sodium alginate,2.0% CaCl₂,10mg/mL 2-mercaptonicotinic acid. The recycling rate of immobilized 2-mercaptonicotinic acid is 84.9%. And the removal rates of the immobilized 2-mercaptonicotinic acid to Cd²⁺,Pb²⁺,Cu²⁺ in solution are up to 79%,97%,84%, respectively. By using of 1.0 mol/L HCl as desorption agent, the chitosan-sodium alginate-mercaptonicotinic acid gel balls which saturated adsorption can be utilized after regeneration. After dealed by three times, the removal rates of chitosan-sodium alginate-mercaptonicotinic acid to Cd²⁺,Pb²⁺,Cu²⁺ are up to 56.9%,69.4%,51.9%, respectivly.As known to us, oyster sance ,rich in amino acids,trace elements and so on , is a kind of very nutritional advanced seasoning, and is more and more loved by consumers. However, because of heavy metal ions pollution and characteristics of processing, the content of heavy metal ions in oyster sauce easily exceed, especially the lead content. Thus, it is necessary to remove Pb²⁺ from oyster sauce to ensure the food security. In the paper, a method of removing Pb²⁺ from oyster sance is developed. In this method, oyster sauce added Pb²⁺ standard is dealed by chitosan-sodium alginate-MT gel balls(ACAMT), which are packed in chromatography column. The results show that there are no significant changes in the contents of amino acid nitrogen,total acid,total solids and so on, but lead content decreases almost by 6 times. By this way, without affecting the nutritional value of oyster sauce, we have solved the problem of lead pollution in oyster sauce well.