Insight into microstructure evolution during starch retrogradation by infrared and Raman spectroscopy combined with two-dimensional correlation spectroscopy analysis

Starch retrogradation is a mechanism that is associated with the quality of starch-based food products; however, the molecular mechanisms underlying this process remain unclear. In this study, we analyzed starch recrystallization by measuring the degree of starch retrogradation, determining the retrogradation enthalpy, and performing scanning electron microscopy experiments. Two-dimensional correlation spectroscopy (2D-COS) was applied to Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy data to further characterize the starch-retrogradation process. We collected and preprocessed FTIR and Raman spectral data on 15 different storage days and then mapped these data using 2D-COS to analyze the ongoing composition changes in starch. Our FTIR- and Raman-2D-COS results revealed 11 and 10 quantitative peaks related to starch retrogradation, respectively. We analyzed the order of specific chemical composition and molecular changes by determining correlations between spectral variables and chemical components; moreover, using these quantitative peaks, we employed a quantitative partial least squares model to establish the degree of starch regeneration based on the retrogradation and associated enthalpy changes. The correlation coefficients of the validation set were 0.943 and 0.972, respectively. These data show that quantitative peaks obtained with 2D-COS analysis can be used to study starch retrogradation quantitatively and have implications for enhancing the quality of starch-based foods.