Further insights into the evolution of starch assembly during retrogradation using SAXS

A new and effective method for evaluating the reassembly of starch molecules at large scale (>2 nm) during retrogradation has been developed based on the small angle X-ray scattering (SAXS) technique. The SAXS curves fitted by the Cauchy plus Power-law functions are decomposed into peak- and non-peak-derived sub-patterns. The peak-derived patterns are used for calculating (i) the size of ordered aggregate structures (d) using Lorentz correction and (ii) the proportion of ordered structures within starch samples (R_peak) by estimating the ratio of the area under the peak-derived sub-pattern (S_peak) to the total area under SAXS curve. The I_max and fractal-like dimension (α) of the scattering aggregates (the fitted parameters of SAXS curve), d, S_peak, S_non-peak (the area under the non-peak-derived sub-pattern) and R_peak change as a function of retrogradation time. Importantly, the S_non-peak interrogates the continuous reduction of amorphous starch molecules during the aging, SAXS parameters including α and d describe starch ordered aggregate structures with larger scale than 2 nm are fitted well with pseudo Avrami equation. The SAXS in this study can be used to unravel the evolution of both amorphous starch structures and ordered aggregates with larger scale during retrogradation.