| The preparation and properties of maleate enzymolysis sesbania gum?MESG?were studied using sesbania gum as a raw material,maleic anhydride as an esterification agent and pyridine as a catalyst.?-1,4-D-mannanase was selected to hydrolyze sesbania gum to provide products with short chains and low viscosity for the further modification,and an ionic liquid was chose as a solvent to increase the substitution degree of esterified derivatives and esterification efficiency.The effect of some factors such as the enzymolysis temperature,enzymolysis time,pH and the amount of?-1,4-D-mannanase,as well as esterification temperature,esterification time,amount of pyridine,amount of maleic anhydride and amount of ionic liquid,on the degree of enzymolysis?DE value?of sesbania gum and substituation degree of maleate enzymolysis sesbania gum was investigated.On the basis of single factor tests,the enzymatic hydrolysis conditions of sebania gum and esterificationenzymatic hydrolysis conditions of enzymolysis sesbania gum were further optimized by the response surface method.The influence of the esterification and enzymolysis on the structure,and thermal properties was studied by Fourier transform infrared?FTIR?,X-ray diffraction?XRD?,thermogravimetric analysis?TGA?,differential scanning calorimetry?DSC?,scanning electron microscope and polarizing microscope?PM?.At same time,the numbers of surface hydroxyl groups,freeze-thaw stability,resistance acid and alkaline,retrogradation and swelling capacity of sesbania gum and its derivatives were also measured.The optimum conditions for preparing enzymolysis sesbania were as follows:enzymolysis time 9 h,enzymolysis temperature 55°C,pH 6.5 amount of?-1,4-D-mannanase236 U/g.The optimum conditions for preparing maleate enzymolysis sesbania gum were as follows:reaction time 80 min,reaction temperature 119°C,amount of maleic anhydride 40%,amount of ionic liquid 1400%.The particle morphology analyzed by polarizing microscope indicated that there were no maltase Maltese crosses on the sesbania gum surface of the gum.The sesbania gum was full and compact,and its surface was smooth,and its size distribution was also uneven.After the enzymatic hydrolysis of sesbania gum,its surface became rough,and many trenches emerged on some of particles.After further esterification on basis of the enzymatic hydrolysis,maleate enzymolysis sesbania gum particles exihited a honeycomb,and a lot of micropores appeared on maleate enzymolysis sesbania gum particles.The XRD spectra showed that esterification almost changed the crystalline structure of maleate enzymolysis sesbania into an amorphous one,whereas the enzymatic hydrolysis less affected the crystalline structure of sesbania gum.The stretching vibration peak of C=O groups in maleate enzymolysis sesbania gum appeared clearly at the wave numbers of 1718 cm-1,and confirming that enzymolysis sesbania gum was successfully esterified in an ionic liquid.The esterification increased the thermal stability of sesbania gum.After sesbania gum being modified by both enzymatic hydrolysis and esterification,its surface hydroxyl numbers were largely reduced.Its solubility,freeze-thaw stability,retrogradation,resistance acid and alkaline were greatly improved except for the reduction in swelling capacity.Adding maleate enzymolysis sesbania could reduce the peak viscosity,trough viscosity,breakdown and setback of potato starch.The elongation at break of the membrane made from maleate enzymolysis sesbania increased,whereas the tensile strength was reduced. |
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