Molecular Ordering Determines the Formation of Strong Gels After Retrogradation of Low-Viscosity Potato Starch

The aim of this study was to characterize a low-viscosity potato starch (LVPS) in terms of pasting properties and kinetics of retrogradation. The pasting properties of a commercial sample of LVPS were measured by Rapid-Visco-Analysis, while the kinetics of retrogradation were assessed following changes in gel strength by mechanical tests (after storage 24 and 168 h, 4°C) and viscoelasticity by dynamic time sweep (4 h, 4°C). Analysis was complemented by measurements of cold-water solubility, thermal properties, Fourier-transformed infrared (FTIR) spectroscopy, polarized microscopy, size distribution, and x-ray diffraction. A sample of normal potato starch (NPS) was used as a control for comparison. LVPS showed significant differences in pasting properties compared to NPS, with much lower pasting parameters (final viscosity 57.9 cP for LVPS, 2991.6 cP for NPS). However, the dynamic time sweep showed that LVPS behaved as a strong gel during retrogradation, which was consistent with the higher gel strength obtained by LVPS after storage. Mechanical and rheological response could be explained by differences in crystallinity and number of oxygen bonds, as suggested by the FTIR spectra. However, the native molecular ordering was different in LVPS, which would determine how amylose leaches during gelatinization and define how self-association and self-assembly take place during retrogradation. Our results also showed that LVPS was not soluble in cold-water, which was consistent with calorimetric data and polarized microscopy images. Hence, LVPS could be further used in applications requiring a starch capable of good mechanical response, but from starchy suspensions with low viscosity.