Kinetics of Structural Changes in Starch Retrogradation Observed by Simultaneous SANS/FTIR-ATR Measurements

Because of the complicated hierarchical structure of starch, starch retrogradation is usually evaluated by combining several structural analysis methods covering various spatial scales. However, structural analyses are typically performed individually, making correlating the structural changes at different spatial scales challenging. Therefore, this study used a simultaneous measurement system comprising small-angle neutron scattering (SANS)/Fourier-transform infrared (FTIR)-attenuated total reflection (ATR) to record multiple structural changes in potato starch during retrogradation. In the SANS patterns, the shoulder-like peak became more pronounced with time. The peak intensity, I _max, representing the amount of ordered semicrystalline structures, increased over time, revealing the orderly reassembly of starch on the nanoscale upon retrogradation. In the FTIR-ATR spectra, the ratio of absorptions (R _1042/1016) at 1,042 and 1,016 cm^-1, indicating the short-range ordered structure in starch, increased during retrogradation. Therefore, the double-helix structures were reformed during retrogradation. The rate constant of the kinetic change for R _1042/1016 was larger than for I _max; thus, changes in the short-range ordered structure of starch converged before the changes in the semicrystalline structure. These results suggest that the formation of double-helix structures of the amylopectin side chain and the structural change of its ordered arrangement could occur in stages during retrogradation.