| Pineapple is one of the largest tropical fruit varieties for trade in the world.Pineapple peel, the by-products from processing of pineapple has developed fewcommercial products which is40%~50%by weight of the original fruit. Pineapple peelhas become a big problem to the development of enterprise due to the lack of effectiveutilization means. Crude fiber, the main components of pineapple, accounts for66.29%indry weight and had no related report on its directly use. This situation led to tremendouswaste of pineapple peel resources. The composition and physicochemical properties ofpineapple peel celluloses prepared by different methods had analyzed in this paper. Thegraft copolymerization of different amino acids on the cellulose modified inhomogeneous ionic liquid systems was investigated and the physicochemical propertiesof the graftcopolymer were analyzed. The optimal conditions of immobilized lipase ondifferent graftcopolymers were studied and the thermostability and the operation stabilityof immobilized lipase were researched. The results provide the theory basis on thecomprehensive utilization of pineapple peel and lipase immobilization research.The results were as follows:(1) Three cellulose samples were successfully obtained by yeast fermentation,lactobacillus fermentation and chemical method, respectively. The crude fiber contents inthe cellulose samples by different methods were85.59%，88.70%and91.98%respectively. The main components in three samples all has been shown cellulose andhemicellulose, but the hemicellulose contents in the celluloses prepared by yeastfermentation and lactobacillus fermentation was higher while the cellulose content waslower than that prepared by chemical method. Acid insoluble lignin contents were all thelowest in three cellulose samples, and it was the highest amount in the cellulose paperedby lactobacillus fermentation while the least amount in the cellulose papered by chemicalmethod relatively.The physicochemical properties of samples prepared by yeast fermentation and bychemical methods has been determined by SEM, XRD, FT-IR and TG-DTG methods.The results indicated that they had the same chemical structure and the same crystal formon the two cellulose samples, their crystal structure belongs to the cellulose I. It was irregular and loose on surface of the cellulose prepared by yeast fermentation, whliedense and stable structure on surface of the cellulose prepared by chemical method.(2) The modification of three cellulose with glycine and serine to form graftcopolymers of pineapple cellulose was studied. The main results were as follows:Cellulose prepared by fermentation was modified with glycine successfully in threeionic liquids AmimCl, BmimCl and EmimCl, respectively. The FT-IR spectra indicatedthat all the three ionic liquids can be used to activate hydroxyl groups of the cellulosemolecules and modify the cellulose. It was in the AmimCl solvent system that themaximum amino acid amount in the grafted polymers was abtained. Because of its liquidstate at ordinary temperature, it is easy for saving melting time, AmimCl was selected assuitable solvent for the graft copolymerization of amimo acid on pineapple peel celulose.Cellulose modification conditions such as the ratio of monosaccharides of cellulosemolecular chain to glycine, reaction temperature and reaction time has been optimized bytaking the amino acid amount in the fiber grafted polymer as index through the responsesurface design method. The optimal conditions for graft copolymerization weredetermined as the ratio of Gly and AGU was2.88(mol/mol), reaction temperature was86.4℃, and reaction time was146min, and under this conditions the amino acid amountin the grafted polymer was21.39mg/g.The structure and properties of Glycine-cellulose grafted polymer papered by yeastfermentation and serine-cellulose grafted polymer papered by chemical method wasstudied. The modified cellulose prepared under optimal conditions were characterized bySEM, XRD, FT-IR, TG-DTG and NMR methods. The results showed that the surface ofregenerated cellulose from AmimCl and modified cellulose appear smooth comparedwith the original rough surface, the crystal structure regenerated cellulose from AmimClchanged into celluloseⅡ from original cellulose I. The crystal structures of modifiedcelluloses were destroyed remarkably. However, the thermal stability of the cellulose andmodified cellulose were all declined. It was showed glycine was successfully grafted ontothe cellulose molecule chains.(3) The conditions of lipase immobilization has been optimized by evaluating theeffect of carrier and enzyme amount, pH value and consentration of buffer solution due tothe activity of the lipase modified onto immodified cellulose. The optimum ratio ofcarriers and lipase was between8:1to12:1(g/g), pH value is between7.5to8.0and theoptimal concentration of the buffer solution is0.03M.Six immobilized lipase was obtained which was immobilized with cellulose-glycineand cellulose-serine by adsorption covalent bonding and entrapment. The maximum amount of immobilized lipase was abatained when the lipase was immobilized withcellulose-glycine by adsorption and cellulose-serine by entrapment. It is92.0%and93.2%, respectively.Comparing the three immobilization methods, the lipase immobilized by adsorptionshowed the best enzyme activity and it is1.21×10~5U/g protein and1.31×10~5U/gprotein, while the activity of enzyme immobilized by other methods showed a decreasetrend. However, it is much higher than that which was reported before.The thermal stability and operational stability of the six immobilized lipase wasstudied. The immobilized lipase and free lipase were incubated at60oC to detect theirthermal stability. And the results indicated that the final residual activity was only10%for the free enzyme, while42%for the immobilized enzyme. After repeated use for30days, final residual activity of free enzyme was only50%, while that of the immobilizedlipase was all more than80%. In conclusion, the thermal stability and operationalstability of the lipase immobilized by modified cellulose were improved effectively. |
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