Investigation on water status and distribution in broccoli and the effects of drying on water status using NMR and MRI methods

Many quality attributes of food products are influenced by the water status and the microstructure. Low-field nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) methods are applied to non-destructively monitor the water status and structure of food. The aim of this study is to investigate the water status and distribution inside broccoli tissues and the effects of hot-air drying on the water status by using NMR and MRI methods. Transverse relaxation times (T2) provide the information of water status and water distribution. Results show that three water fractions with different T2 relaxation times were detected inside broccoli, which corresponded to different cell compartments. Proton weighted imaging could monitor the spatial distribution of water. Image analysis indicates that the water distribution inside broccoli was heterogeneous and the water content reduced from the stalk to the buds. During hot-air drying experiments, different drying kinetics were observed in the florets and stalks, which were related to their different structures. In addition, a detection limit of the moisture content was calculated for LF-NMR (about 11.35%). The results of this study show that the low-field NMR and MRI methods can precisely provide the quantitative information of water status inside food materials, and can be used to investigate the effects of food processing on product quality. The method provided in this study can be used to monitor changes of water status and distribution in a sample non-destructively during drying process.