Study On The Preparation And Properties Of Oxidized Waxy Corn Starch

With waxy corn starch as raw material, the preparation technology and properties of oxidized starch were studied in this thesis. It includes, the conditions of process of sodium hypochlorite, hydrogen peroxide, potassium permanganate oxidized starch and dialdehyde starch, the comparison of transparency, dissolution, swelling capacity, retrogradation, freeze-thaw stability and viscosity among sodium hypochlorite, hydrogen peroxide, potassium permanganate oxidized starch, the comparison of the ability of adsorb urea between three kinds of oxidized starch and dialdehyde starch. Study on the morphology, gelatinisation property and thermal properties through scanning electron microscope (SEM), infrared spectroscopy (IR), amylograph and differential scanning calorimetry (DSC) was conducted. The effect of oxidation on the properties of the starch was also analyzed. The results are as follows:The conditions of process of starch oxidized by sodium hypochlorite is:amount of sodium hypochlorite addition is3%of starch, temperature40℃, reaction time2h, pH9.0, the content of carboxyl and carbonyl prepared oxidized starch are0.538%and0.093%, respectively.The conditions of process of starch oxidized by hydrogen peroxide is:10%hydrogen peroxide dosage, reaction temperature is45℃, the reaction time for3h, system pH8.0, the content of carboxyl and carbonyl prepared oxidized starch are0.451%and0.108%.The conditions of process of starch oxidized by potassium permanganate is:2.0%potassium permanganate,4.5%sulfuric acid, reaction temperature at50℃, the content of carboxyl and carbonyl prepared oxidized starch are0.465%and0.046%.The conditions of process of dialdehyde starch is:the ratio of sodium periodates and starch was1:1, the temperature was30℃, the reaction time is2hours, the pH of the reaction was3.0, the aldehyde content of prepared sample could reach80.32%.Some paste properties of sodium hypochlorite, hydrogen peroxide, potassium permanganate oxidized starch were studied. The results show that, the paste properties of three kinds of oxidized waxy corn starch including dissolution, swelling capacity, retrogradation and viscosity are superior to those of the native starch, but freeze-thaw stability of potassium permanganate oxidized starch and hydrogen peroxide oxidized starch is inferior to the native starch. Comparison of adsorption capability of urea between three kinds of oxidized starch and dialdehyde starch, dialdehyde starch have a higher adsorption capability of urea than other three kinds of oxidized starch, hydrogen peroxide oxidized starch had a lowest adsorption.The results of Scanning Electron Microscope (SEM) indicate that, the granules of waxy corn starch presents polygons, smooth surface, particle surface without corrosion and damagephenomenons. Compared with native starch, starch after oxidized modification, the surface of starch granule becomes rough, with varying degrees of depression and fold, the greater of the oxidized degree, the more obvious of particle surface.The results of Infrared spectroscopy (IR) reveal that, after sodium hypochlorite, hydrogen peroxide and potassium permanganate oxidized modification, new chemical groups ate introduced in starch molecules, there is an obvious COOH characteristic absorption peaks in1605cm-1.1604cm-land1596cm-1, which indicates that carboxyl occurs during oxidized modified. After sodium periodate oxidized. there is an obvious C=O characteristic absorption peaks of dialdehyde starch in1743cm-1, which shows that the group of aldehyde group are introduced.The results of pasting properties show that, after sodium hypochlorite, hydrogen peroxide and potassium permanganate oxidized modification, the pasting temperature is lower than that of native starch. The more the degree of modification increases, the lower the peak viscosities of paste, but after sodium periodate oxidized, the pasting temperature is higher than that of native starch, the more the degree of modification increases, the lower the peak viscosities of paste.The results of differential scanning calorimetry (DSC) plots illustrate that, compared with that of native, the onset temperature of sodium hypochlorite. hydrogen peroxide and potassium permanganate oxidized starch decreases. And with the degree of oxidation increases gradually declines, enthalpy decreases obviously at the same time, the higher the degree of oxidation, the more obvious of the decrease. With the content of aldehyde increased, the onset temperature of the starch is enhanced more significant. This indicates that after aldehyde group introduced, part of the double helix structure of starch granules is destroyed. As a result, less energy is needed and enthalpy decreased.