Effect of Enzymatic Hydrolysis by Pullulanase on the Physicochemical Properties of Kudzu Starch

The effect of pullulanase enzymatic hydrolysis on the physicochemical properties of granular kudzu starch was studied. The gelatinization property, content of resistant starch, thermal characteristic, morphology, particle size, crystal structure and molecular structure of kudzu starch (KS) and enzymatic hydrolysis kudzu starch (EHKS) were determined by rapid viscosity analyzer (RVA), differential scanning calorimetry (DSC), polarizing microscope, scanning electron microscope (SEM), laser particle sizer, fourier transform infrared spectrometer (FTIR) and X-ray diffraction (XRD), respectively. The results showed that after the enzymatic hydrolysis of KS, its peak viscosity and breakdown value decreased by 28.33% and 94.69%, respectively, while the trough viscosity, final viscosity and setback value increased by 12.53%, 12.47% and 12.37%, respectively. And the content of resistant starch increased from 1.29% to 4.60%. After the enzymatic hydrolysis of KS, its polarized cross still existed, but the granules expanded and the particles size became large. And the surface layer was peeled off. DSC endothermic peak of modified starch shifts to high temperature region, but its endothermic enthalpy decreased. The enzymatic hydrolysis promoted the formation of short-range ordered structure of starch molecules. After the enzymatic hydrolysis of KS, its relative crystallinity decreased from 37.31% to 29.10%.