Studies On Functional Properties Of Konjac Glucomannan Fragment

Konjac glucomannan(KGM)is a water-soluble glucomannan with high molar mass,and its have been widely applied in the field of oil drillings,food additives,medicine and gels for its great unique rheological properties and functions.Currently,its research mainly focuses on its extraction,purification,physical and chemical modification,pharmacological activities,as well as molecular structure and chain configuration.The literatures about the production and biological activities of konjac glucomannan oligosaccharides have also been reported.But there is less development on the konjac glucomannan with the molecule weight between these two types mentioned above.In this paper,degradation of KGM Fragment with different molecular weights by y-irradiation,and its physical,chemical characters were investigated.The main results are as follows:(1)Compared with konjac glucomannan without y-irradiation treatment,the analysis of UV?IR and RM spectrum indicated that the characteristic function groups of G-2?G-3 and G-4 had not changed greatly.There was absorption peak near 890 cm-1,which means that the three ploysaccharides were all ?-glycosidic linkage.There were absorption peak near 810 cm-1 and 870 cm-1,indicating the existence of mannan.According to the data of the intrinsic viscosity of KGM and its weight-average molecular weight,the Mark-Houwink equation for the KGM samples gave[?]= 3.16×10-2 M0.772.The ? value showed that KGM molecules are solvated in the form of semi-flexible chain in water.The molecular dynamics simulation method was introduced to discuss the chain conformation of KGM samples.The results indicated that KGM with suitable Mw could form intra-molecular hydrogen bonds easily,which can strengthen its stable conformation in aqoeous solution.(2)KGM samples in aqueous solution exhibits pseudoplastic behaviour,its viscosity decreases quickly with the increasing of shear rate.While increasing the molecular weight,concentration of KGM,temperature and ionic strength,the viscosity increases,and all the samples can form reversible weak gel at a certain condition.The gelation time of KGM gels became longer and the rate constant of gelation decreased with decreasing molecular weight or concentration of konjac glucomannan or temperature or concentration of ionic strength.And in comparison with K+,Ca2+ obviously has significant influence on KGM.It may be the Ca2+ that builds salt bridges among KGM random chains,thus helps the formation of the ordered network regions of chains cross-linked by bonds within a finite reacting time.(3)Edible films prepared from konjac glucomannan(KGM)with different molecular weights were characterised with respect to the influence of molecular weight on its properties.The data from SEM showed that the surface of film become further soothe with decreasing molecular weight,and only a very small granular exised in material.And the film prepared from KGM with lower molecular weight has higher WVP,this may attributed to an increase in the number of shorter chains.The tensile strength increased initially with decreasing molecular weight,and then decreased with further reduction in molecular weight.Conversely,tensile elongation exhibited the opposite trend.It indicated that KGM with suitable Mw could form better physical and chemical properties membranes.