Rheological,GelProperties And Granule Morphology Of Acetylated Potato Starch

Acetylated starch is one of the most commonly used modified starches in food industry,its rheological and gel properties are related to the starch based food's processing and storage properties.Starch is a natural macromolecular compound,in order to ensure enough sample,three different kinds of potato starch from different manufacturers were selected,the acetylated starches(substituting degree was around 0.1)were prepared by acetylation of vinyl acetate and acetic anhydride,and the rheological and gel properties of the modified starches were studied.In addition,the effect of acetylation on the structure of starch granule is not clear.In this study,the limited enzymatic hydrolysis method was used to study the shell structure and blocklets of acetylated starches.The rheological properties of three kinds of potato starches and their acetylated starches at 6%,8% and 10% concentrations were studied through rotational rheometer.It was found that the starch pastes' rheological characteristic values of peak viscosity,valley viscosity,final viscosity and consistency coefficient increased with the increase of concentration,the variation range of acetylated starches' characteristic values was smaller than that of the raw starch,and the variation range of the two kinds of acetylated starches were close.The results of static rheological test at 6% concentration showed that :(1)Acetylation did not change the flow type of potato starch,two kinds of acetylated starches and raw starches were all pseudoplastic fluid with no yield stress,and there was shear thinning phenomenon.(2)The viscosity values of the acetylated potato starches(valley viscosity,final viscosity and consistency coefficient)were higher than that of the raw starches,the viscosity values of the acetic anhydride acetylated starches were higher.(3)Acetylation increased the thixotropy of potato starch,the acetic anhydride acetylated starches had the strongest thixotropy and the worst shear stability.The dynamic rheological test results showed that acetylated starches had better thermal stability,the changingtendency of acetylated starches on elastic modulus G' and viscous modulus G'with temperature was more gentle,Compared the two kinds of acetylated starches,the thermal stability of acetic anhydride acetylated starch was better.The textural properties of three kinds of potato starch gels and their acetylated starch gels at the concentration of 6%,8% and 10% were studied through texture analyzer,it was found that the acetylated starches' gel forming ability was poor,their hardness and gumminess values were lower compared with the raw starches,the greater the concentration,the greater the decrease degree.The microstructure of the gels was observed by scanning electron microscopy after freeze-drying,the results showed the network of the raw starch gels was more uniform,and the size of their meshes was more homogeneous in the range of 150-270 ?m.The network of acetylated starch gels partly collapsed,and their mesh wall fractured because the network has lower strength,therefore,the mesh size of acetylated starch gels changed in a large range.Compared with the vinyl acetate acetylated starches,the acetic anhydride acetylated starches' network was more loose,the neighboring mesh walls collapsed caused the amalgamation of these meshes lead to a larger lamellar structure.The freeze-thaw stability tests of the starch gels showed that the freeze-thaw stability of vinyl acetate acetylated starch gels were good,and the freeze-thaw stability of the acetic anhydride acetylated starch gels and the raw starch gels were poor.A method for the observation of the shell structure and bolcklets of acetylated potato starch was established: the enzymatic hydrolysis of acetylated starch was taken palce under the condition of starch concentration was 100mg/mL,alpha amylase concentration was 100 U/mL,the temperature was 25?and the reaction duration was 24 hours,starch granules were observed by scanning electron microscope after washing,alcohol washing and air drying.Three kinds of potato starches and their acetylated starches were studied by this method,it was found that the hydrolysis only occurred on the surface of the particles,the starches remained their granular state after enzymatic hydrolysis.The surface blocklets of the raw starches and acetylated starches occured after enzymatic hydrolysis,the acetylation of low degree of substitution had no obvious effect on the morphology and size of the bloccklets in potato starch,the blocklets were spherical or ellipsoidal with a size of 30-60 nm.The enzymatichydrolysis rate of vinyl acetate acetylated starches and acetic anhydride acetylated starches were 3.3%-3.5% and 2.8%-3.1%,respectively,which were higher than that of the raw starches(0.6%-0.8%).The intermolecular interaction of acetylated starches is weak,the acetylated starches' shell structure was easier to expose after enzymatic hydrolysis.