Preparation Of Chitin Oligosaccharides And Research On Bioactivities Of Chitin Oligosacchar Ides

Chitin is the second most abundant natural biopolymer after cellose, which is obtained from the exoskeleton of invertebrates and the cell walls of fungi. Chitosan is obtained after alkaline deacetylation of the chitin. Chitin and chitosan are saccharides that attract much attention on the biomedical, pharmacological, agricutual, and biotechnological fields. However, recent studies on chitin have attracted interest for converting chitin to its oligosaccharides, because chitin oligosaccharides are not only water soluble, but also possess special fuctional properties such as antitumor activity, immunostimulating effects, and antimicrobial activity.Chitin oligosaccharides can be prepared by enzymic methods. However, chitin has poor solubility in water, the hydrolysis rate is low because of the heterogeneous conditions , and higher oligomers can not be obtained in good yield. Now, water-soluble chitin has been prepared, and chitin oligosaccharides can be prepared under homogeneous conditions by unspecific enzymic hydrolysis.This research reports the preparation of chitin oligoccharides from water-soluble chitin by unspecific enzyme hydrolysis such as cellulase and pectinase. The optimum conditions for depolymerizing water-soluble chitin are as follows: depolymerizing by cellulase, pH 6.3, temperature 55 ; depolymerizing by pectinase, pH 5.1, temperature 55, and the weight ratio of cellulase or pectinase to substrate was 1 .' 10. The complex enzyme composed of cellulase and pectinase performs higher depolymerizatized activity than a single enzyme like cellulase or pectinase does. Ultrafiltration was used to isolate the chitin oligosaccharide after the depolymerization, the yield rate of chitin oligosaccharide, with molecularweight below 6,000, hydrolyzed by cellulose, pectinase and complex enzyme was 68.2% , 52.3 % ^ 72.7 % , respectively. The degree of deacetylation and the degree of polymerization of the hydrolysates produced by cellulose are analysed. The (GlcNAc)n from dimer to octamer has been shown by TLC, HPLC and TOF-MS, and the degree of deacetylation of chitin does not changed after converting into oligosaccharides.Three kind of partially deacetylated chitooligosaccharides (COS I , D.D.32%; COS II, D.D.49%; COSIII, D.D.95%) has been prepared for bioactivity research. Their scavenging activities are inverstigated against superoxide radical and hydroxyl radical by the method for determination of luminesecence. The peroxidization of PUFA inhibitory activity is also inverstigated. The results show that the chitooligosaccharides have scavenging effects on the superoxide radical and hydroxyl radical, and chitooligosaccharides also have the inhibitory activity of the peroxidization of PUFA. In addition, COSIII with relatively high degree of deacetylation shows the highest radial scavenging effects on the superoxide radical and hydroxyl radical, and the highest inhibition of the peroxidization of PUFA. These results indicate that the antioxidant effects of chitooligosaccharides depend on their degree of deacetylation and concentration.Angiotensin I converting enzyme (ACE) inhibitory effects of chitooligosaccharides have also been inverstigated. The values of TIA of COS I , COS II and COSlIIare 0.121 mU/g, 0.175 mU/g and 0.448 mU/g, respectively. COSIII with relatively highest degree of deacetylation exhibites the highest ACE inhibitory activity. So the ACE inhibitory activity of chitooliogosaccharides is dependent on the degree of deacetylation and concentration.