Unravelling temperature-dependent molecular changes in hydrated wheat and maize starches using 1H time-domain NMR

This study proved that time-domain NMR (TD-NMR) experiments can accurately demonstrate the interaction between starch (wheat and maize) and water and the distribution of water molecules in starch-water systems during heating. Molecular properties in starch-water systems at 50% moisture content were monitored by Rhim and Kessemeier – Radiofrequency Optimized Solid-Echo (RK-ROSE) and Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences at frequent (2 °C intervals) measurements during heating (55–80 °C). Starch-like and water-like phases were obtained by RK-ROSE and CPMG pulse sequences, respectively. The second moment, M2, along with the relaxation times of the populations, associated with fast-decaying protons, provided information on the crystal structure state during heating and the extent of gelatinisation. The relaxation times of the most abundant population from the CPMG signal decreased during heating due to strong interactions between starch and water. Temperature of stabilisation of this population aligned with the associated findings from the differential scanning calorimetry and rheological measurements.