Synthesis And Properties Of Citric-chitosan

Nowadays, as the global environmental pollution and resource waste is becoming more and more serious, human has been facing with rigorous energy crisis. In some coastal regions in our country, there are many shrimps and crabs being hunted and bred every year, but after processing, the leftovers of shrimps and crabs are always detruded to form lots of wastes such as carapaces. The accumulation of carapaces will pollute environment; therefore, chitin extracted from carapaces will not only solve the problems of the waste deposit but also achieve the goal of recycle, which is in favor of environment protection.Chitin, an abundant and renewable biological resource with a structure as similar as cellulose, is the only one alkaline polysaccharide in the natural world. Chitosan is a product after deacetylation of chitin. With its numerous excellent properties, chitin and chitosan are widely used in many fields such as chemical, agriculture, medical, environment protection and so on. However, because of its poor solubility, the further application is highly limited. As a result, how to make water-soluble chitosan becomes the emphasis and hot focus of chitin research of domestic and foreign scholars, in which Carboxylation is the most common and effective ways.Using chitosan as the raw material, in this paper, we have successfully synthesized citric acid-chitosan for the first time, and then compound it with alginate sodium, finally we obtained fixed nitrile hydratase carrier with high biological activity. Firstly, through single-factor experiments, the effects on chitosan carboxylation by the citric acid dosage, reaction time and reaction temperature have been studied respectively, and then based on that, using Design Expert Software, the synthesis parameter of citric acid-chitosan has been optimized with Response Cutting Plane method. The best parameters for citric acid-chitosan sythnesis with Box-Behnken method are as follows: citric acid itosan (n/n)= 2.56:1, reaction time =3.56h, reaction temperature=61.7℃. Under this best condition, the substitution degree of citric acid-chitosan reached 2.25 and the average viscosity-molecular weight reached 285,000. After water-soluble research, we find that with the increase of substitution degree of citric acid-chitosan, its water solubility firstly increases and then decreases, when substitution degree is 1.4, its water solubility reaches the best.In the experiments that using citric acid-chitosan-alginate as fixing nitrile hydratase cell carrier, firstly through signal-factor experiments, the effects on relative enzyme activity and mechanical property of nitrile hydratase-fixed cell by dosage of citric acid-chitosan-alginate solution and fix time have been discussed. And then on the basis of signal-factor experiments, three factor and four level orthogonal experiment has been designed to optimize the optimum technical parameter of the experiment. The best condition finally obtained are as follows: volume ratio of citric acid-chitosan-alginate / nitrile hydratase solution (v )=10:1, the best fixing time=2h, the substitution degree of citric acid-chitosan=0.7, the mass percentage of citric acid-chitosan=0.8%, the mass percentage of calcium chloride =5%. Under this optimum condition, the nitrile hydratase-fixed cell with high enzyme activity and mechanical property has been obtained and the relative enzyme activity value reaches 131%.