Characterization And Kinetic Model For Controllable Enzymatic Hydrolysis Of Konjac Glucomannan And Application In Membranes

Konjac Glucomannan (KGM) and enzyme-modified KGM derivatives have beenused extensively in many applications, from hydraulic fracturing fluids in enhancedoil/gas production to food additives and gels, because of their ability to modulaterheological properties and functions. In this thesis, operating parameters of hydrolysis,molecular chain parameters of KGM, size exclusion chromatography (SEC) ofwater-soluble polysaccharides, process analysis, mathematical modeling, pH-triggeredenzymatic degradation and formation of membranes by enzyme-modified KGMderivatives have been integrated applied to systemically investigate enzymaticdegradation of KGM by β-mannanase from the viewpoint of theory, experiment andapplication. The main conclusions in this thesis are drawn as following. Operating parameters of hydrolysis and molecular chain parameters ofKGM: The enzyme was deactivated by boiled water. Enzymatic hydrolyzed KGMsamples had a Mark-Houwink-Sakurada (MHS) relationship of[η] = 4.07×10?4 Mw 0.733dL/g, and a characteristic ratio of 6.56 as determined bymulti-angle laser light scattering (MALLS), SEC and dilute solution viscometer. SEC of water-soluble polysaccharides: The universal calibration curve isobtained, lg[η]M w = ?0.7733Ve +14.277 , by using dextrans and mannose aspolymer standards. For KGM, the peak elution volume is found to decrease with flowrate, which means that the polymer molecules look bigger at higher flow rates. Thismay be due to the press-induced change of polymer conformation and longitudinaldiffusion. The flow rate and polymer concentration effect on the MWD is also studied.1.0mL/min and 0.05% are confirmed as flow rate and polymer concentration for SECanalysis in this thesis. Chromatographic analysis on enzymatic degradation of KGM: During theKGM degradation process, the molecular weight of KGM decreased with reactiontime, while the molecular weight distributions (MWD) obtained from SEC broadenedfirst and then narrowed. According to the hydrolysis mechanism, there are four factorsthat can be interpreted the variations of MWD: ①the distribution of enzyme andsubstrate in the solution, ②the heterogeneous of KGM backbone, ③differentpathways of the enzymatic scission during degradation, ④the binding patternbetween enzyme and substrate. IIEnzymatic degradation kinetics: Based on the Michaelis-Menton equation andchanges in molecular weight, kinetic models were established to simulate thehydrolysis process, and it was demonstrated in good agreement with the experimentalresults. In very dilute polymer solutions, reaction rate increased with first-orderkinetics with substrate concentration. In the concentration range during 0.1%~1%, theenzyme/polymer binding sites were saturated, and the degradation kinetics waszero-order. The whole enzymatic degradation of concentrated KGM may be acombination of zeroth- and first-order reactions. pH-triggered enzymatic degradation of KGM: Experiment result shows thatpH value can effectively trigger the enzymatic degradation of KGM. This reversible,pH-triggered degradation may be a result of the resolve of enzyme which isprecipitated by adjusting the pH to 4. Formation of membranes from KGM and enzyme-modified KGMderivatives: Three kinds of membranes were prepared from KGM andenzyme-modified KGM derivatives by coagulating NaCO3 solution and by blendingwith Xanthan gum, respectively. The chemical structure, morphology and mechanicalproperties of these membranes were investigated. Experiment results showed thatKGM with suitable Mw could form better physical and chemical propertiesmembranes.