| In this paper, the removal of Cadmium(Cd) from shellfish homogenate was studied. Molecularly imprinted crosslinked chitosan resin (MICCR) was prepared. The method of the adsorption and removal of Cd which was extracted from shellfish homogenate using citric acid by MICCR was established. The main contents and results were as following:(1) The spectral properties of Cd (?), citric acid and their complexes were studied by ultraviolet spectrophotometry. The formation conditions and composition of the complexes of Cd-citric acid were examined. Correspondence solutions reference method was used to obtain stability constant of the complexes. The results showed that, the conditions to obtain the most stable complexes were pH4.5, ratio of Cd (?) and citric acid was 1:1, the conditional stability constant ?'=4.09×105, the stability constant ?= 7.1×105, lg?= 5.85.(2) Preparation and Characterization of MICCR:MICCR was prepared using chitosan by complexes of Cd-citric acid as the template, glutaraldehyde as crosslinking agent, through the principle of molecular imprinting technique and characterized by infrared spectroscopy and scanning electron microscopy, et al. The results showed that, the production rate of MICCR was 56.3%, when the amount of glutaraldehyde was 4.5mL, crosslinking temperature was 80? and crosslinking time was 3h. The N atoms of amino group and O atoms of primary and secondary hydroxyl were participated in the process of preparation of MICCR and the adsorption of Cd (?) by MICCR. There were coordination reaction between complexes of Cd-citric acid and chitosan and then complexes of Cd-citric acid was eluted as a whole. The three-dimensional structure which was propitious to adsorb complexes of Cd-citric acid took shape. The adsorption of Cd (?) by MICCR actually was through the adsorption of complexes of Cd-citric acid. Compared with chitosan, MICCR had higher crystalline degree and did not soften and dissolve under acidic conditions, and the thermal stability was enhanced.(3) Adsorption performance of MICCR on Cd:Adsorption experiment of Cd(?) from aqueous solution by MICCR was conducted. The results showed that, the adsorption capacity of Cd(?) was 170.4mg/g and the optional pH value was 4.5. The dynamic model and second order kinetic model were applied to fit the experimental data, respectively. The adsorption of Cd(?) by MICCR were well described using the second order kinetic model with the adsorption rate of 6.97g·g-1·h-1 and R2=0.9905, the calculated equilibrium adsorption capacity of 183.5mg/g is close to the experimental equilibrium adsorption capacity of 170.4mg/g, further verifying that the adsorption of Cd(?) fitting to the second-order kinetics model better. Langmuir and Freundlich models were applied to describe the adsorption behavior of Cd(?) by MICCR and Langmuir model better to fit the process. Therefore, the adsorption of Cd(?) was monolayer adsorption. The theoretical maximum equilibrium adsorption capacity of Cd(?) by MICCR through Langmuir model was 214.6mg/g. The repeated adsorption of Cd(?) by MICCR in five times showed little change in the adsorption capacity. The adsorption capacity of Cd(?) by MICCR was stable which proved that the cross linking reaction and molecular imprinting technique could improve the regeneration properties of chitosan.(4) The effects of removal of Cd(?) from five species of shellfish homogenate by MICCR:Cd(?) was extracted from five species of shellfish homogenate by citric acid and then was removed from extracted liquid of Cd-citric acid by MICCR. The effects of the process of the extraction and removal of Cd(?) on the protein, amino acids and trace elements of shellfish homogenate were studied and the nutritional values of proteins were evaluated by methods of chemical score and essential amino acids index. The results showed that, the extraction rates of Cd(?) from homogenate of Pteria martensii, Oyster, scallop, Mytilus viridis and Pteria penguin by citric acid were 92.2%,61.2%,61.3%, 65.4% and 92.3%, under the conditions of 0.08mol/L of citric acid, pH4.0,1:10 of material to solution (m:V)and 4h. The removal rates of Cd(?) from extracted liquid of Cd-citric acid by MICCR were 99.2%,80.8%,98.7%,73.1% and 96.2%, under optimum conditions of 0.05g/mL MICCR, pH value 4.5 and treatment time 8h, indicating that MICCR had showed perfect effects in the removal of Cd(?) from extracted liquid.(5) After the removal of Cd(?), proteins in Shellfish homogenate had partial loss. However, the compositions of amino acids of proteins in eliminated liquid were complete, which were complete proteins. The contents of total essential amino acids to total amino acids were 21.4%?33.3%, EAAI was 43.85%?56.63%. The compositions of amino acids of proteins were more balanced, reasonable, which belonged to high-quality protein. There still were certain amounts of trace elements of Ca, Mg, Se, Mn, Cu, Zn and so on, which were beneficial to human health. Therefore, after the removal of Cd(?) from Pteria martensii, Oyster, scallop, Mytilus viridis and Pteria penguin, the eliminated liquid could be used for the development of other product. |
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