Study On Retrogradation Of Oxidized Starch

Oxidized starch was one of the most widely used modified starches in industry. It was usually used at various environments as paste, so its retrogradation was a key problem in its application. Previous literatures mostly focused on its production process and application development, but its retrogradation was seldom reported, so the retrogradation of oxidized starch was systematically studied in this paper.The effects of oxidation levels, sugar and inorganic salt, storage temperatures and moisture contents on retrogradation of oxidized starches were studied from multi angles by break properties measurement, turbidimetric method, measurement of syneresis, X-ray diffraction, measuring the resistance to enzymatic hydrolysis, DSC and so on. The genesis of retrogradation and the relations between the factors and retrogradation were discussed. The results were:1. As the oxidation level was higher and higher, the retrogradation of oxidized starches decreased at the beginning and then increased. When the oxidation level was lower, the retrogradation was mostly influenced by amylase, carboxyl and carbonyl contents. While the amylase content decreased, and the carboxyl and carbonyl contents increased, the retrogradation decreased. When the oxidation level was higher, the molecular weight had a great effect on retrogradation. While the molecular weight decreased, the retrogradation increased in some extent.2. Both sucrose and glucose increased the retrogradation rate of oxidized starch. As the concentration of added sucrose and glucose was increased, the retrogradation rate also increased. The effect of glucose was more effectively than sucrose. Inorganic salt retarded the retrogradation, and only a bit of salt could decrease retrogradation effectively. As the concentration of added salt was increased, the retrogradation rate gradually decreased.3. The oxidized starch sample stored at 4℃had the highest crystallinity and retrogradation degree, the sample stored at 25℃had the lowest crystallinity and retrogradation degree, and the sample stored at -18℃had intermediate crystallinity and retrogradation degree. When the gelatinized starch was stored at 4℃, the retrogradation rate calculated by Avrami equation was 1.21 times of that stored at -18℃, and 1.67 times of that stored at 25℃. The gel structure of oxidized starch sample which was stored below 0℃would be reinforced and form a spongy porous structure.4. After storage for a long time (>7 d), the oxidized starch sample with more moisture content retrograded more easily, while moisture content ranged from 70% to 85%. Otherwise, at early stage (≤7 d) the moisture contents had little effect on retrogradation.The research results provided a theoretical foundation for producing oxidized starch products with good storage stability and high quality. These would also be of great guiding significance for developing the uses of oxidized starch and improving the properties of oxidized starch.