Study On The Improvement Of Viscoelasticity Of Corn Starch By Konjac Gum And The Inhibition Of Waxy Corn Starch Retrogradation By Enzymatic Modification

Natural starch has many disadvantages,such as easy aging,weak pseudoplasticity,difficult to form,poor water resistance,and unsuitable for patients with hyperglycemia.The addition of konjac gum to corn starch can significantly improve the viscoelastic properties of konjac gum corn starch paste mixture,and the enzymatic modification of waxy corn starch can improve the physical and chemical properties of waxy corn starch.In this paper,the viscoelastic properties of gelatinized mixtures of different proportions of konjac gum corn starch and the inhibition of retrogradation of waxy corn starch by enzymatic modification were studied by using modern analytical instruments,and the relationship between the molecular structure and retrogradation of waxy corn starch modified by enzymatic method was explored,which provided theoretical basis for improving food processing technology and the inhibition of starch retrogradation by enzymatic modification,as well as for starch composition The application of branching enzyme in industry can improve the theoretical reference.Firstly,in order to investigate the effect of konjac gum on the viscoelastic properties of corn starch,the dynamic rheometer was used to study the viscoelastic properties of konjac gum corn starch paste mixture.The results show that the power low model can effectively characterize the rheological properties of konjac gum corn starch paste mixture.The gelatinized mixture of konjac gum and corn starch is a pseudoplastic fluid.Compared with corn starch paste alone,with the increase of the amount of gum,the viscosity of the gelatinized mixture increases and the pseudoplasticity increases.The results of dynamic viscoelasticity test showed that with the increase of frequency,both G'and G'increased,and the tangent value of loss Tan?<1,which reflected that the addition of konjac gum made the gelatinized mixture have superior viscoelasticity.When the mass ratio of konjac gum to corn starch is 0.4:0.8,the gelatinized mixture has the smallest elasticity and the largest viscosity.The gelatinized mixture has a better synergistic thickening effect,that is,the fluid flow characteristics of the gelatinized mixture is significant.Secondly,the enzyme was obtained by transformation and expression of the target gene,and purification.The effect of pH value and temperature on the activity of amylase was studied with the glucose produced by the reaction of amylose and branching enzyme as the evaluation standard.The results showed that the optimum pH and temperature of the enzyme were pH 4.5 and 65?,respectively.Thirdly,the molecular structure of waxy corn starch modified by recombinant starch branching enzyme was studied.The waxy corn starch modified by different enzyme amount(0.1 U,0.15 U,0.2 U)was determined by ion exchange chromatography(HPAEC).The results showed that the degree of polymerization of amylopectin increased with the increase of enzyme amount,The short chain of DP<6 decreased from 3.74%to 0.98%;the short chain of DP(6-12)increased from 21.45%to 23.69%without significant change;DP(13-24)increased from 41.84%to 47.78%,while the chain length of DP(24-36)decreased from significant difference compared with the control group;the long chain of DP?37%decreased from 14.68%to 12.29%.The results showed that the number average molecular weight(MN)decreased from7.41×10~7 g/mol to 2.59×10~7 g/mol,the weight average molecular weight(MW)was9.86×10~7 g/mol?1.69×10~7 g/mol,the root mean square rotation radius(RZ)was 191nm?91.52 nm,and the dispersion coefficient(PDI)was 14.22?6.43.The results showed that with the increase of enzyme content,the content of SDS in the modified waxy corn starch increased significantly(P<0.05),ranging from 11.07%to 24.11%,and the content of ready digestible starch increased significantly(P<0.05),RDS)was significantly reduced 84.59%?75.38%and RS was significantly reduced4.34%?0.51%compared with the control group.The results showed that with the increase of enzyme activity,the increase of glucose concentration slowed down gradually,and the amount of glucose released in vitro decreased,which indicated that the enzyme modified waxy corn starch had the ability of delaying digestion.Finally,the inhibition of starch regeneration was studied by differential calorimetry(DSC)and the iodine absorption and branching degree of the enzyme modified starch were measured by enzyme marker.The results of DSC showed that the modified waxy corn starch could inhibit the long-term regeneration after being stored at 4?for 3 days,7 days and 14 days respectively.The results of iodine absorption and branching test showed that with the increase of enzyme amount,the maximum absorption peak moved to the direction of wave length(blue shift phenomenon),from 615 nm to 595 nm;amylase could significantly improve the branching degree of waxy corn starch.Therefore,the main reason for the inhibition of long-term retrogradation of waxy corn starch modified by recombinant starch branching enzyme may be that starch branching enzyme reduced the molecular weight,the content of straight chain,the average chain length of branch chain and formed new branch points of waxy corn starch.