Enzyme-catalyzed Controllable Degradation Of Konjac Oligo-glucomannan And The Basic Application Of Its Gelation

The research was supported by the project of the Key TechnologyR&D Program of China “The scale treatments and application ke ytechnology of konjac glucomannan”(No.2007BAE42B04) and wascentered on the biodegradation of Konjac glucomannan (KGM). Theresearch studied the effect of hydrolytic factors on the degradationproducts (middle-to-high molecular weights konjac glucomanna n(MH-KGM)) of native KGM, and va rious molecular weights MH-KGMwere prepared. Otherwise, the research studied the gelation behaviorand pri mary application of MH-KGM with various molecular weights.The results were shown as follows:(1) The β-mannanase was used to catalytic degraded native KGMand the influence of the enzyme concentration, pH, temperature,substrate concentration, reaction ti me on the degradation products’molecular weight (Mw) and molecular weight distribution (D) werestudied through the single factor experiment. The optimal te mperaturewas50℃and when temperature increased, the D values were increasedfirstly and then decreased. The optima l pH was7.5; the D value was notchanged at low pH and increased at the optimal pH. The Mw ofdegradation product was sensitive to enzyme dosage because theenzyme a ctivity was very high. The D value was decreased with theincreasing of the substrate concentration, while the Mw of degradationproduct was decreased. The D value and Mw were decreased with timeand trended finally. The results of orthogonal experiment showed thatthe effects of various factors on the molecular weight of degradationproducts were in the following descending order: enzy me concentration＞substrate concentration＞pH＞temperature＞time; the effects ofvarious factors on the molecular weight distribution were in thefollowing descending order: enzy me concentration＞te mperature＞pH＞substrate concentration＞time.(2) In this work, carbamide was used as the anti-gelation agent, optimization of substrate concentration, carbamide concentration,alcohol washing times and drying temperature respectively on effectsof the yield of MH-KGM powder which purified and prepared by thetechnology of ethanol precipitation. The results showed that conditionsof high productive yield are: substrate concentration1.5%, carbamideconcentration10%, alcohol washing times3, drying temp erature50℃.(3) The FT-IR spectra of native KGM and MH-KGM with variousmolecular weights were completely identical. Otherwise, the X-raydiffraction indicated that they had similar but slightly differentdiffraction peaks and all of them showed characteristics ofamorphousness. From ther mal analysis, a significant loss of massoccurred at about218,225and270℃for native KGM, MH-KGM B andMH-KGM A, respectively. At50%weight loss, the decompositiontemperatures of native KGM, MH-KGM B and MH-KGM A were around309,300and334℃. From the SEM analysis, it can seem clearly thatMH-KGM powder was less compact and more porous compared tonative KGM powder, and the smaller the molecular weight was, themore obvious is the feature.(4) The molecular weight, mo lecular chain parameter andrheological property of MH-KGM with various molecular weights wereanalyzed by SEC-MALLS and advanced rotation rheometer. TheSEC-MALLS results pointed that relative stiffness parameter βincreased from0.38to0.80when KOGM Mw decreased from1.07×106to2.854×104, it implied that lower molecular weight MH-KGM tendedto be mo re rigidity. The rheological analysis indicated that storageshear modulus G’ and the loss shear modulus G’’ increase and the lossfactor tan decrease with the increasing of the molecular weight ofMH-KGM, the concentration of MH-KGM and alkali concentration,which indicates that the gels get more elastic and stable.(5) In this research, a pH-sensitive interpenetrating polymernetwork (IPN) hydrogels designed for colon targeted drug deliverywere prepared by using MH-KGM with various molecular weights andpoly(acrylic acid)(PAA) with N,N-methylene-bis-(acrylami de) (MBAAm) as the cross-linker. The structure of the hydrogels wascharacterized by FT-IR and SEM. The swelling ratio of these hydrogelshad sensitive respondence to the environmental pH value variation.Hydrogels composed of higher molecular weights MH-KGM had biggerswelling ratio than those hydrogels which composed of lower molecularweights MH-KGM.MH-KGM with different molecular weights can show variousphysicochemical properties and physiological func tion. At the present,many of studies concentrated in the native KGM. Various molecularweights MH-KGM were studied and applicated little because it difficul tto prepare various molecular weights MH-KGM systematacially.Therefore, it’s very i mport ment to realize the controllable degradationof native KGM.