Study On Preparation Of Slowly Digested Starch By Compound Enzyme

Corn starch is an important traditional food resource,but this natural organic resource has defects such as poor water solubility and poor stability,and the starch is hydrolyzed by enzymes to generate glucose,which easily enters the blood through the small intestinal mucosa,resulting in relatively high glycemic index(GI)fluctuations.It cannot meet the daily consumption needs and processing needs of high-quality food of special groups such as diabetics.This requires the use of some technical means such as physical,chemical or enzymatic methods to change its original physical and chemical properties to prepare a new type of functional food that can slowly digest and absorb in the body,release energy for a long time,and have special physiological properties.Based on dietary nutrition intervention of carbohydrates on human health and chronic diseases,Slowly Digestible Starch(SDS)has the function of preventing metabolic diseases and is widely accepted.The enzymatic modification reaction test conditions are mild,the cost is low,the product safety is high,and the environmental pollution is less.Therefore,this topic usesα-amylase and branching enzymes to enzymatically modify natural corn starch,explores the best preparation process of slow-digesting corn starch,and characterizes the structure and physicochemical properties of SDS with different enzyme modification times.On this basis,SDS was applied to carrot noodles to prepare a functional diet with high SDS content.The main findings are as follows:1.The preparation process of enzyme-modified starch was established.Slow-digesting starch was prepared by modifying corn starch withα-amylase and branching enzyme(BE).Single factor and response surface tests were designed to investigate the effects of four factors,including enzyme dosage,enzyme action time,enzymatic hydrolysis temperature and starch slurry concentration,on the content of SDS in enzyme-modified products,and to determine the preparation process parameters of enzyme-modified corn starch to prepare SDS.The results showed that the order of the influence of each single factor on the SDS content was:enzyme action time,enzyme addition amount,enzymatic hydrolysis temperature,and starch slurry concentration,and the interaction among the four factors was not obvious.The equation is:Y(%)=37.42+1.32A+0.62B+0.59C+0.33D+0.072AB-0.24AC-0.22AD-0.16BC-0.027BD-0.15C D-3.03A~2-1.44B~2-2.49C~2-2.29D~2.The model fit F value was 0.69(>0.05),p<0.0001,and there was a good correlation between the predicted value(37.66%)and the true value(37.28%),which further indicated that the model had a good fit and Small experimental error.The optimal preparation conditions were as follows:the enzyme action time was 6.5 h,the enzyme addition amount was 320 U/g starch,the enzymatic hydrolysis temperature was 75.5℃,and the starch slurry concentration was 21.5%.Under this condition,the SDS content was 37.28%.2.Characterization of enzyme-modified starch.Using a polarizing microscope to observe the change of starch cross polarization,the natural corn starch appeared birefringence;while the pregelatinized modified starch polarization cross completely disappeared.Scanning electron microscopy(SEM)was used to study the morphological changes of starch and its derivatives.It was found that most of the natural corn starch granules had a polyhedral structure with smooth edges and corners,with uneven surfaces and pores.The granule morphology has been completely lost.With the increase of enzymatic hydrolysis time,the surface of starch granules has different degrees of concave and pore structures.In the method of characterizing the internal structure of starch molecules before and after enzyme modification,gel chromatography(SEC-MALLS-RI)was used to determine the relative molecular mass and relative molecular dispersion of starch.The relative molecular weights of starch and amylopectin showed a decreasing trend with the increase of enzyme modification time.And with the increase of BE enzymatic hydrolysis time,the degree of molecular dispersion in amylose tends to 1,while the molecular distribution in amylopectin is gradually uneven;ion chromatography(HPAEC-PAD)was used to determine the content of starch before and after enzymatic modification Chain segment distribution,the proportion of short chains(A chain,DP≤13)of enzyme-modified starch increased significantly,and the A chain content of corn starch was 55.65%.The proportion of medium and long chains(B chain,13<DP<30)and long chains(C chain,DP≥30)continued to decrease.It is speculated that the long chain of glucan is hydrolyzed by enzymes and undergoes glycosyl transfer to make starch debranched products.The branched segments move to a shorter direction,thereby obtaining a hydrolyzate with a higher proportion of branched and short chains.The crystallinity of starch molecules was measured by X-ray scattering technology,and it was found that with the increase of enzyme action time,the relative crystallinity of starch gradually decreased.,the starch crystal structure also changed from typical type A to type B,and the crystallinity decreased by 19.48%;the chemical shift of starchα-1,6glycosidic bond was determined by nuclear magnetic resonance technology to study the change of starch branching ratio,which is similar to corn starch.The content of a-1,6 glycosidic bonds of enzyme-modified starch increased by 10.53%;the solubility of enzyme-modified starch was greatly improved,and the solubility in water reached 29.79%;the enzyme-modified starch also had low viscosity and thermal stability.Compared with natural corn starch,the content of slow-digestible starch increased by 13.22%.It is speculated that reducing the multi-scale structure of starch and increasing the ratio of a-1,6 glycosidic bonds will help to improve the slow-digesting performance.3.Slow-digest carrot noodle development.The enzyme-modified slow-digestible starch was replaced by 30%of the high-gluten flour to prepare slow-digestible carrot noodles.Taking high-gluten flour and common corn starch samples as controls,the application study found that the in vitro digestion curve was flat with the addition of 30%SDS,and the SDS content reached28.61%,which was much higher than the other two samples.The sensory evaluation results of three kinds of carrot noodles found that the hardness,chewiness and viscosity of carrot noodles with SDS were lower than those of the control samples;the addition of SDS could improve the properties and functions of carrot noodles,but it would affect its taste and appearance more or less.