Abstract: This study aimed to verify the impact of moisture distribution status on thermal characteristics of starch from newly harvested maize. Two maize cultivars in northeast China, Zhengdan 958 and Xianyu 335, were used in this study. Low field nuclear magnetic resonance (LF-NMR) and differential scanning calorimeter (DSC) were applied to study changes in water migration and distribution status in maize kernels during 60 days of postharvest storage and changes in thermal characteristics of maize starch were also examined. The results showed that the relaxation time (T2) and water distribution changed significantly (P < 0.05) during the postharvest storage period. For both cultivars, the melting enthalpy of maize starch gels reached a maximum value of 18.54 and 15.06 J/g at 40 d after harvest, respectively. There was a significantly negative correlation between the relative area (A21) and the relaxation time (T21) of bound water and moisture content of maize grains (P < 0.01). In addition, A21 was significantly correlated with endothermic enthalpy (ΔH) of starch gels (P < 0.05). Accordingly, changes in the crystal structure of starch may be partly related to water migration and distribution status. LF-NMR can effectively analyze the dynamic changes of moisture during the postharvest storage of maize and its effect on the functional properties of starch.

Key words: maize starch, water mobility, LF-NMR, thermal characteristics