Optimization Of Preparation Process Of Compound Sweet Potato Starch Modified By Enzyme And Their Physicochemical Properties

The branched structure of amylopectin plays a crucial role in the physicochemical properties of native starches.The objective of this study focused on the modification by the complex action of various enzymes to change the branch density and chain length distribution of the starch,thereby improving physicochemical properties.Sweet potato starch was used as the material to be combined action of branching enzymes?BE?,?-amylase?BA?and glucosyltransferase?TG?to modify sweet potato starch,so as to evaluate the degree of starch physico-chemicalization at different branching degrees.The degree of branching of sweet potato starch was as the evaluation index,the factors and levels of the experiment were selected on the basis of the single factor test,and the Design-Expert software was used to optimize the modified sweet potato starch using Response Surface Methodology based on the Box-Benhnken Center combined experimental design principle.Degree of branching,the results show that the optimum degree of branching of sweet potato starch when the corresponding compound enzyme preparation process conditions:the amount of branching enzyme 300?/g,enzymatic hydrolysis time 9h;?-amylase enzyme addition amount 10?/g,enzymatic hydrolysis time9h The amount of glucosyltransferase added was 9000?/g,and the enzymolysis time was9h.under this condition,the branching degree of sweet potato starch can reach 48.68%.The results of chain length distribution indicated that the natural sweet potato starch had a certain change in the molecular structure of starch through the combined action of BE,BA and TG.With the increase of branching degree,the average chain length and the average degree of polymerization of the product gradually decreased,which indicates that the modification of natural sweet potato starch through complex enzyme may produce a cluster structure material with high proportion of short chain and high branch density.In order to further study the effect of different branching structures of starch modified by complex enzyme method on the physicochemical properties of starch.The solubility of the modified starch was measured and compared.The main findings are as follows:1?The branching degree of natural starch was 16.99%,the percentage of?-1,6glycosidic bonds was 12%,and the branching degrees of enzyme-modified sweet potato starch were:25.76%,30.73%,35.85%,40.97%,44.99%,48.68%,respectively.Percentages of corresponding?-1,6 glycosidic bonds are 20%,24%,27%,29%,30%,and 32%,respectively.Compared with natural sweet potato starch,the degree of branching of enzyme-modified sweet potato starch and the ratio of?-1,6 glycosidic bonds were significantly increased.Therefore,a highly branched modified starch can be produced through the combined action of BE,BA and TG.2?The sweet potato starch showed four strong diffraction peaks near 15.0°,17.2°,18.2°,and 23.5°at 2?,and a weak diffraction peak near 19.7°.It is a clear C_A-type crystal structure and relatively crystalline.The degree was 38.8%,and the original peak intensity of the enzyme-modified sweet potato starch at 15.0^o,17.2^o,and 18.3^o became weak,and the original peak at 23.5^odisappeared.In contrast,the peak at 19.7°is relatively increased,and new diffraction peaks appear at 13.1°.Therefore,the crystal structure of native starch was completely destroyed,and the damaged crystal structure may be entangled and rearranged into a mixture of C-type and V-type,and the V-type crystal is the main crystal form.The relative crystallinity of the enzyme-modified starch was lower than that of the natural sweet potato starch,but the crystallinity of the enzyme-modified starch increased with the increase of the branching degree of the enzyme-modified starch.The relative crystallinity was 13.8%,14.6%,15.0%,13.4%,15.9%,and 16.9%,respectively.3?The original infrared spectrum of modified sweet potato starch had almost the same absorption peak band between 900-4000 cm^-1,and there are only slight differences in absorption peak intensity and peak position.In the deconvoluted spectrum,the peak intensity ratios of 1047 cm^-11 and 1022 cm^-11 increase with the branching degree.This indicates that the branching structure has a significant effect on the(1047 cm^-1/1022 cm^-1)ratio.4?The solubility of native and enzyme-modified sweet potato starch were 14.57%,45.56%,53.46%,55.92%,57.96%,62.31%,65.37%,respectively.Compared with native starch,the solubility of enzyme-modified sweet potato starch was significantly improved.And with the increase of branching degree,the solubility of starch shows an increasing trend,so the starch branching degree has a great influence on the solubility.The native starch paste solution is more transparent,and the enzyme-modified starch paste solution appears milky.Compared with native starch,the enzyme-modified starch had lower rejuvenation than native starch,and the degree of retrogression gradually decreased with the increase of branching degree,indicating that the branching degree had a significant effect on the retrogradation of starch.5?The native sweet potato starch with the concentration of 6%and the complex enzyme modified starch paste all showed pseudoplastic fluids,and the shear stress increased gradually with the increase of the shear rate.At the same shear rate,the shear stress of enzyme-modified starch paste is much smaller than that of natural sweet potato starch,and the shear stress gradually decreases with the increase of branching degree.The viscoelasticity measurement results show that the starch paste shows a typical weak gel three-dimensional network.With the increase of branching degree,G'and G"decrease,indicating that the rigidity,strength and viscoelasticity of the gel decrease as the branching degree increases.The loss factor tan?value of the enzyme modified starch is lower than that of native starch.The viscous and elastic components of the enzyme-modified starch were lower than those of the control group,but the increase of the branching degree contributed to the increase of the tan?value,and the tan?value increased with the increase of the branching degree.6?The native starch has typical gelatinization properties,with a large gelatinization and endotherm in the range of 62.5?to 74.21?.The gelatinization peaks of all enzyme modified starches disappeared,indicating that the original crystal structure after enzyme modification treatment destroyed.