Study Of Depolymerization Of Chitosan With The Aid Of Immobilized Enzymes

Chitin,poly-β-(1,4)-N-acetyl-D-glucosamine, is the second most abundantrenewable organic resource on earth. Chitosan is the deacetylated derivative ofchitin. Even though chitin and chitosan have very strong functional popertiesin many areas, but chitin and chitosan is difficult to dissolve in water, diluteacid and other organic solvents because of the extensive hydrogen bondingamong the molecule of polymer. Hence, the utilization of chitin/chitosan hasbeen hampered by its insolubility in practical solvents.Chitin and chitosan oligomers possess additional functional propertiessuch as good water-solubility, humectancy and humidity, anti-microbialactivity, antitumour activity and immuno-enhancing effects. So thechitooligosaccharides can be used in many areas such as functional foods,biomedication, cosmetics, medical diagnose and biophysiologic.There are many methods of degrading chitin and chitosan, such as acidhydrolysis, oxidative degradation and enzymic hydrolysis. It needs manyreagents in the process of oxidative degradation, so it is very difficult toseparate and purify the oligomer. Also the molecular weight of xoidativedegradation products is too high (about 10,000). Even though the method ofacid hydrolysis has been employed in industry, the molecular weight ofdegradation products is extensive. It's very difficult to get the products ofspecific molecular weight and the environment contamination is severe in acidhydrolysis because of employing the stong acid. Chitosan can be depolymerizeto specific molecular weight products by enzymic hydrolysis. The yield ofoligosaccharides with a high degree of polymerization(DP) was greater afterenzymic 11ydroIysis than after acid hydrolysis. Also the reactive condition ofenzymic hydrolysis is mild and it is easy to control the l.eaction process.ImmobiIized enzymes have n1a11y 111erits comparing with free e11zymes.There are lots of researchs on immobilized enzymes with chitosan as carrier,such as cellulase. paPain, trypsin, urease, diastase, xylanase, tannase. lipaseand polyphenol oxidase. 'l'his researcI1 selected tl1e llO:l-specific el1zyl11es:papain, pectinase and celIulase to in1111ohiIize on chitosan with gIutaraIdehydeas cross-linking agent. The optimum conditions of immobilization were quest.Then chitosan was hydrolysis by the immobilized enzymes and the optimumconditions of hydrolysis were quest. At last the hydrolysis products wereseparate by the fractional precipitation with methanol-propanone solvent.This research certified that it's practicable and efficient that papain,pectinase and cellulase were imtnobiIized on chitosan with glutaraldehyde.The recovery of immobilized enzymes activity was 78.0l%, 82.53% and84.86% respectively. The optimun1 an1ount of enzyme immobilized onchitosan was 25mg/g chitosan. The optimum temperature and time ofglutaraldehyde react with chitosan were ambient temparature and 8 hourrespectively. The optimum pH of the immobilized enzyme was 8.0 for papainand cellulase, whereas the optimum pH of immobilized enZyme was 7.0 forpectinase.There were many reports on degrading chitosan with non-specificenzymes, but usil1g immobiIized non-speciIic enzyn1es to hydrolysis cl1itosanwas rare. Tl1is research employed iml11obiIized papain, pectinase and cellulaseto llydrolysis chitosan and measured the degree of degradation by the contentof reducil1g sugar in the reactive solution. The optimum condition ofhydrolysising chitosan by in1lnobilized papain and pectinase were reactive pH3.5, telnperature 50C; The optimuI11 col1ditiol1 of hydroIysising chitosal1 byldriobllized cellulase was that reactive pH 4.5, temPeratue 50 t. The0btlthhin ptoportioti of itnmobillzed etizymes to chitosan was 8:l for threekirids of imgiobilized enzymes. The effectiveness of hydrolysis bylininobillzed cellulase was the best, whlle the effectivetiess of hydrolysis bylmmobillzed pectihaSe was better than by itnmobilized paPain. F...