Phase Transition Of Starch And Its Effect On Starch Digestibility During Processing

Processing methods and processing conditions affect the structure and digestion of starch.Therefore,it is important to study the effects of processing methods and processing conditions on the gelatinization and digestibility of starch.This study mainly studied the effect of different heating temperatures and heating time on the structures of wheat starch samples with wide water content,the similarities and differences between starch samples with similar and different degree of gelatinization(DG)about structure and digestibility,and the effect different processing methods(hydrothermal treatment and ultra-high pressure treatment)on the structure of starch.The research results were as follows:The gelatinization behavior of wheat starch was investigated using starch-water mixtures that were heated under different conditions.Heating starch-water mixtures at 50? a temperature below onset temperature(To)of starch gelatinization,resulted in disruption of long-and short-range ordered structure,as measured by DSC,XRD and LCM-Raman.And the extent of disruption was greater when starch was heated at higher water content.At low water content(23?44%),heating duration had little effect on gelatinization behavior of starch,whereas at higher water content(54?75%),longer duration of heating resulted in greater disruption of multi-scale structure of starch.From this study,we concluded that gelatinization endotherm of starch does not represent the complete gelatinization behavior.Three DG gradients were selected:23.5-27.3%,75.4?78.8%and 95.9?97.1%,respectively.The multi-scale structure and digestibility of wheat starch samples with similar and different DG were investigated.When DG gradients increased from 23.5-27.3%to 95.9?97.1%,the degree of structural damage also increased.In general,there was a little difference in the multi-scale structure between wheat starch samples with similar DG but in different heating conditions.Lower water content,higher heating temperature and longer heating duration resulted in better ordered structure for samples with similar DG.For the wheat starch samples with similar and different DG,there was no significant difference in the digestibility.This might be due to the change of shell and holes by heating treatment made a greater accessibility of enzymes to the amorphous and crystalline regions to enhance enzyme hydrolysis.The starch samples were pretreated by different processing methods(hydrothermal and ultra-high pressure treatment)and then gelatinization behavior of starch were investigated.The results showed that To,Tp and Tc increased as the DG gradually increased for the samples of temperature-induced gelatinization;while To,Tp and Tc did not increase significantly with the increase of DG for the samples of pressure-induced gelatinization.The ultra-high pressure treatment caused a greater destructive degree of short-range order.The sample of pressure-induced gelatinization had a slightly lower viscosity than that of temperature-induced gelatinization.Intact granules were still observed when starch was fully gelatinized after ultra-high pressure treatment.The above results showed that the effects of ultra-high pressure and hydrothermal treatments on multi-scale structure were very different under the similar DG.