The Characterization Of Ordered Structure Of Amorphous Starch And Its Effect On Starch Digestibility

Native starch has a very complex multi-scale structure,The crystalline structures,which contain the long-and short-range molecular order of double helices in starches,have important influence for functional properties of starch.Compared with crystalline structure,the amorphous structures in starch or amorphous starch are poorly understood,but the order of amorphous structure have an important contributions to functional character of starch.In the present study,we prepared wheat and potato amorphous starches by heating with different water contents and different time respectively.We determined short-range molecular orders by ATR-FTIR and Raman spectroscopy.Additionally,the in vitro starch digestibility of the amorphous starches was evaluated.The main research methods and results are as follows:Preparing different wheat and potato amorphous starch samples according control the water contents,and divided the samples into the block form and the powder form.The X-ray diffraction results demonstrated that all of the starch samples are amorphous starch,the crystal structure of starch is destroyed during heating.For block amorphous starch samples,the absorbance ratio of 1022/995 cm-1 in ATR-FTIR and the relative area and intensity of Raman bands at 480 cm1-have a better linear correlation with the water:starch ratio(1022/995 cm-1 of ATR-FTIR has a positive relationship with water content,the correlation coefficient R2 are 0.88,0.89 respectively;the relative area and intensity of Raman bands at 480 cm-1 has a negative relationship with water content,the correlation coefficient R2 are 0.80,0.87,0.95,0.90 respectively).Suggesting that the swelling extent of starch increased with increasing water content,the molecular order(short-range molecular order of amorphous structure)is decreased gradually.But the powdered starch samples did not show any significant differences in IR ratio and area and intensity of Raman bands with water:starch ratio,suggesting that the short-range molecular order of amorphous starch is destroyed by milling.The in vitro enzymatic digestibility shows that the in vitro digestion rate constant k value of block amorphous starch had a better linear correlation with the short-range molecular order,suggesting that short-range molecular order of amorphous starch can affect the digestibility to a certain extent.Compared with water content,heating time has little effect on the swelling extent of starch granules.For block amorphous sample heating at different times,the spectral parameters had no correlation with the heating time.It suggests that the short-range molecular order of the amorphous starch prepared under this condition have a small difference.In the absence of changes in the short-range molecular order,the digestion rate of block amorphous sample are still have differences,there may be related to the texture of the samples,and need to research further.According the research,We established a spectral analytical method to characterize short-range molecular orders in amorphous starch,which were determined by ATR-FTIR and Raman spectroscopy.And it was found that the short-range molecular order of amorphous starch can affect its in vitro enzyme digestibility to a certain extent.Compared with the difference in the short-range order of amorphous starch caused by the moisture content,the heating time has little effect on the ordered structure of amorphous starch molecules.