Effects Of Annealing On The Retrogradation And Enzymatic Hydrolysis Of Wheat Starch

Annealing is a physical process to modify the metal materials for desirable properties at the earliest.As far as the bio-macromolecules such as starch,protein and nucleic acid are concerned,the annealing treatment,is only involved the water and thermo-process at a low cost and in an environmentally friendly way.And that preparation of modified starch by annealing improves the rheological,gelatinization and retrogradation property of starch and increase the application value of starch.In this paper,wheat starch was used with a single-step annealing treatment to analyze the effect of annealing on the retrogradation and enzymatic hydrolysis properties by modern instrument and the relationship between the internal mechanism of annealing and retrogradation as well.The main conclusions are as follows:1.The effect of annealing on the retrogradation of starch during storage was demonstrated by DSC.Three annealing parameters were varied,namely moisture(50-90%),time(0.5-48 h)and temperature(35-50 °C).The results suggest that 25%(w/v)annealed wheat starch samples stored at 4 °C for 7 days had smaller DR values than native wheat starch under the same storage conditions.XRD indicated that annealed wheat starches stored at 4 °C for 7 days had fewer recrystallizations than native wheat starch.Next,the changes of the rate of retrogradation of wheat starch during storage were observed,and Avrami equation described the retrogradation kinetics of wheat starch.The results showed that the retrogradation rate of wheat starch was 1.2-2.0 times that of annealed wheat starch,and also proved that annealing decreased the retrogradation rate of wheat starch.2.The native wheat starch and the wheat starches annealed at 50°C were observed by using Scanning Electron Microscope(SEM)and Laser Particle Size Analyzer(LPSA).The results showed that surface of the annealed wheat starch granule had no obvious changes,and the average particle size of starch granule increased.3.The changes of enzymatic hydrolysis rate(EHR)of wheat starch before and after annealing were observed,and the correlation between annealing modification and the mechanism of enzymatic hydrolysis in wheat starch had been further explored using DSC ? SEM and XRD.The results found that the EHRs of annealed wheat starches were obviously higher than the ones of native wheat starches,and the EHR variation on annealing time and annealing temperature was outstanding.Native wheat starch and annealed wheat starch exhibited increased peak gelatinization temperatures(Tp)and mostly decreased gelatinization enthalpy(?H)on enzymatic hydrolysis,and there was a change in gelatinization characteristics parameters for different annealed wheat starches.SEM showed that there were no differences with regard to patterns of enzymatic granules between native wheat starches and annealed wheat starches.The relative crystallinity of annealed wheat starches was higher than that of native starches,and both of the relative crystallinity on native and annealed starches increased after enzymatic hydrolysis.Annealing accelerated the EHRs of wheat starches,and the various of annealing had different effects on EHRs of wheat starches.