Study on water proton distribution and flow status of starch during the hydration process

The hydration process of starch significantly affects the quality of starch-based food, especially for samples with medium to low water content. In this paper, rice starch, as a representative of cereal starch, and potato starch were chosen as the samples. The proton distributions and flow status of the hydrated rice starch and potato starch with moisture contents of 20–90% and the causes of the differences between them were investigated by 1H LF-NMR. The longitudinal and transverse proton relaxation (T1 and T2) of the two starch systems was obtained using the inversion recovery (IR) sequence, the free induction decay (FID) sequence, and the multi-pulse echo CPMG sequence. Through the detection of longitudinal relaxation, two different populations were found in the two hydrated starch systems, and the changes were linearly related to the moisture content. Through the detection of transverse relaxation, two populations were distinguished in the hydrated rice starch samples with different moisture content, whereas two to four different populations were detected in the hydrated potato starch samples. Because of the differences in particle size and swelling capacity, hydrated potato starch showed greater proton freedom and more observable types of protons than hydrated rice starch.