Effect Of Annealing On The Physicochemical Properties And Enzymatic Hydrolysis Of Kudzu Starch

Annealing is a hydrothermal treatment that changes the physicochemical properties of starches by improving crystalline perfection and by facilitating interactions between starch chains.The extent of these changes being influenced by starch composition and by the arrangement of the starch chains is within the amorphous and crystalline domains of the native starch granules.In this paper,starch from roots of kudzu was isolated and subjected to annealing treatment at 50℃ for 24 h,72h,120 h,168h in 1:4 starch to water ratio(w/v).Modern instruments was used to study the influence of annealed kudzu starch on apparent amylose content,swelling power,solubility,pasting characteristics,thermodynamic properties,transparency,freeze-thaw stability,rheological measurements,gel texture,X-ray crystal structure and enzymatic hydrolysis properties.The main conclusions are as follows:1.The native kudzu starch and the kudzu starches annealed were observed by using Scanning Electron Microscope(SEM)and Laser Particle Size Analyzer(LPA).The results showed that most native kudzu starch granules were irregular polygon,a few were ellipsoidal,annealed particle morphology did not occur significant changes.The particle size distribution of the original root starch and annealed root starch was normal distribution,and the particle size of the root starch was decreased by annealing treatment.After annealing treatment of kudzu starch compared with the native starch,apparent amylose content increased,swelling power and solubility,transparency decreased,freeze-thaw stability,gel strength increased,and annealing does not change the Kudzu starch "shear thinning behaviors".2.Using Differential Scanning Calorimetry(DSC)and Rapid viscosity Analyzer(RVA)analysis,and compared to the native starch,annealing treatment increased the gelatinization temperature(T0,Tp,Tc),gelatinization temperature range was shortened(△T = Tc-T0),gelatinization enthalpy(△H)was increased and the gelatinization peak temperature time increased.The breakdown value decreased after 72 h annealing treatment,reduced the occurrence of the breakdown phenomenon of starch paste.3.Using X-ray Powder Diffraction(XRD)and Fourier Transform Infrared Spectroscopy(FT-IR)observed that annealing does not change the crystal type of kudzu starch,C-type pattern with main peaks at 2θ for 15.3°and 17.3,and relative crystallinity is higher than that of native starch,1022cm-1/1047 cm-1 ratio increased with the aid of the results of X-diffraction,the 13 C NMR spectra showed that annealing does not change the content of kudzu starch relative double helix,improvedthe parallel packing and untwisted end of double helix.4.The changes of enzymatic hydrolysis rate of kudzu starch before and after annealing were observed,and the correlation between annealing modification and the mechanism of enzymatic hydrolysis in kudzu starch had been further explored using DSC、SEM and XRD.Annealing treatment of kudzu starch hydrolysis rate was higher than that of the native kudzu starch,enzymolysis rate measurement and scanning electron microscopy(SEM)observed that α-amylase hydrolysis rate higher than glucoamylase hydrolysis rate,gelatinization peak temperature(Tp)increased after enzymolysis,relative crystallinity was lower than the native starch,proved that the enzymatic hydrolysis is simultaneously carried out in the amorphous region and the crystalline region of the starch.