Preparation And Biological Activities Of Chitosan Derivatives

Chitosan is natural cationic bio-polymer which exists rare in nature. Chitosan possesses many beneficially properties, such as abundance, inexpensive, non-toxicity. non-irritant,non-immunogenicity,non-mutagenicity,biodegradability,biocompatibility. Much attention has been paid to its agriculture, medicine, food industry, light industry and environmental protection.This paper chose (3-chitin as the research project, and used it as raw material preparing chitosan with the condition of high concentrated alkali, high temperature, and ultrasonic assistant method. The main reaction conditions were:50%NaOH. the temperature of80℃, solid-liquid ratio1:10, reaction time2h, and ultrasonic frequency25kHz. Two kinds of chitosan derivatives carboxymethyl chitosan and low molecular weight (LMW) chitosan were prepared and their antioxidant ability and bile acid binding capacity were measured. The DS of carboxymethyl chitosan was measured by acid-base titration method, molecular weight of chitosan and chitosan oligosaccharide were measured by viscosity method and the characterization of sample was analyzed by FT-IR.First, we investigated reaction factors such as the amount of sodium hydroxide and chloroacetic acid, reaction temperature and reaction time on the effect of the degree of substitution (DS) of carboxymethyl chitosan. The study of factors influencing DS of carboxymethyl chitosan indicated that the amount of sodium hydroxide significantly affected the DS, followed by the amount of chloroacetic acid, reaction temperature and reaction time. The optimal reaction conditions were:1.5g chitosan added5mL50%sodium hydroxide solution,4.5g chloroacetic acid, reaction temperature60℃and reaction time4h. The maximum DS of carboxymethyl chitosan was1.59in the optimized conditions. Compared with the conventional preparation methods, using squid cartilage as raw material could greatly improved the DS of products and the water-solubility of products were better.Second, H2O2concentration, reaction temperature and reaction time on the effect of the yield of water-soluble chitosan were investigated. The result indicated that reaction temperature significantly affected the LMW chitosan yield, followed by the reaction time and H2O2concentration. The optimal reactions were:9%H2O2, reaction time5h, reaction temperature65℃. The maximum yield of LMW chitosan was78%in the optimized conditions.Third, the antioxidant and bile acid binding properties of carboxymethyl chitosan were investigated. The results showed that carboxymethyl chitosan had better scavenging ability toward DPPH radical, hydroxyl radical, superoxide radical, reducing power, chelating Fe2+ability and bile acid binding capacity than that of raw chitosan. The introduction of hydrophilic carboxymethyl groups on chitosan decreased the intramolecular and intermolecular hydrogen bonds resulting in the exposure of more amino and hydroxyl groups, thus the biological activity of chitosan improved.Fourth, the antioxidant and bile acid binding properties of LMW chitosan were studied. The results showed that LMW chitosan had better antioxidant ability and bile acid binding capacity, and with the decreasing of molecular weight, the antioxidant ability and bile acid binding capacity of LMW chitosan improved. Its probable reason is that after degradation by H2O2, the molecular chain of chitosan was disrupted, the molecular structure became loose, thus its reaction activity enhanced.