Water molecular dynamics during dough heating by Fast Field Cycling Nuclear Magnetic Resonance

Measurements of the water 1H Nuclear Magnetic Resonance (NMR) relaxation rate R1 in hydrated starch (SW), gluten (GW) and dough (WD) were performed at different frequencies using Fast Field Cycling, at 20, 40, 60 and 80°C and again at 20°C after cooling. The originality of this study lies in the measurements performed during the heat-induced dough transformation to investigate the impact of temperature on water distribution and interaction with other dough constituents. Rather than measuring NMRD on off-line heated samples, real-time heating and cooling was applied directly in the spectrometer in such a way that sample temperatures were fully controlled when measuring R1 at various frequencies. Measurements before heating enabled the detection and interpretation of potential differences in the dynamics of each sample’s NMR Dispersion (NMRD) profile. At low temperatures, water dynamics in WD and interactions with other dough constituents were dominated by the interaction of the water with starch granules. The NMRD profile for GW differed significantly from the others, suggesting that gluten retains more water when it is mixed with starch. By heating each sample, the inhibitory effect of gluten on hydrothermal changes in starch (swelling and gelatinization) was confirmed. Last, the competitive interactions between hydroxylated groups of each macromolecule and the hydrogen in water molecules were shown to be continuously driven by chemical exchanges that influenced R1 values in all samples.