Self-assembly Mechanism In The Progress Of Starch Retrogradation And Its Effect On Starch Digestibility

Starch retrogradation has an undesirable effect on the quality of starchy foods.A thorough understanding of starch retrogradation plays an important role in maintaining the quality of starchy foods during storage.In this study,we investigated the behavior of starch retrogradation under different conditions.The effect of water content(33%-80%)on starch retrogradation using differential scanning calorimetry(DSC)was investigated.The calculated retrogradation percentage of starch samples with low water content was higher than 100%.By the analysis of DSC results,we have demonstrated for the first time that at low water contents,the enthalpy change of retrograded starch is higher than that of native starch.According to the results of ATR-FTIR and LCM-Raman,the molecular order of reheated retrograded starch samples is lower than that of DSC gelatinized starch.These findings have led us to conclude that enthalpy change of retrograded starch at low water contents involves not only the melting of recrystallized starch during storage,but also residual starch crystallites after DSC gelatinization.Very low or high water contents do not favor the occurrence of starch retrogradation.We prepared two starch gels with different water content(33%-60%)by simulating the heating program of DSC using RVA.The gels were stored at 4 ? for different time,and then the retrogradation gels were freeze-dried and ground into powder.From the results of DSC and XRD,retrograded starch gels containing 33%water presented an A-type pattern,those containing 50%and 60%moisture gave a B-type pattern,and samples with moisture content of 43%displayed a C-type pattern.Retrogradation enthalpy of rice samples with 33%and 60%water content significantly increased at 14 and 4 days,respectively.For wheat starch,samples with 43%and 50%water contents presented the similar trend of retrogradation enthalpy.At water content of 33%,enthalpy change of retrogradation samples increased significantly at 4 and 14 days,and retrogradation enthalpy of 60%water containing samples increased significantly from 4 to 14 days.These results indicated that higher water content led to a faster significant increased enthalpy change of retrograded samples,which is also variety-dependent.By nonlinear fitting,we found that the enthalpy change and relative crystallinity displayed an exponential function.By analyzing starch digestion results,we found that SDS content increased initially and then decreased with increasing storage time,but RS content presented an opposite trend.With increasing water content,the time for the SDS content from increase to decrease and RS content from decrease to increase became shorter.These findings suggested that low water content resulted in slow migration of starch chains and molecular arrangement,and then retarded the nucleation,propagation and perfection progress of amylopectin crystallites.Therefore,more imperfect crystallites formed.However,high water content led to opposite results.