Studies of hardness and water mobility of cooked wild rice using nuclear magnetic resonance

The changes in hardness and molecular mobility of water of cooked wild rice during 10 days storage were investigated in this study. Seven grades of wild rice were subjected to various degrees of soaking and cooking and were stored at 5C. Nuclear magnetic resonance (NMR) technique was employed to determine the free induction decay (FID) signals and spin-spin relaxation time constants (T₂) of protons, which was regarded as a measure of rotational molecular mobility of water in the samples. Multi-component behavior of FID signals was observed, based on which water molecules in the samples were classified into three fractions with different T₂s. The hardness of the samples was assessed using a texture analyzer. All samples firmed over the storage period, which correlated well with the changes in NMR parameters. A multiple variable regression model was proposed to describe the relationships between firming and NMR parameters in the wild rice samples. The model demonstrates the possibility of using NMR parameters to assess and predict the firmness of the samples during storage.