Convenient use of low field nuclear magnetic resonance to determine the drying kinetics and predict the quality properties of mulberries dried in hot-blast air

ABSTRACT The drying kinetics and quality properties of mulberries dried in hot-air were investigated at four temperatures (40, 50, 60, and 70 °C). A convenient tool, Low-field nuclear magnetic resonance (LF-NMR) and MRI techniques were used to study the water state and distribution during the drying process. The results showed that the water reached equilibrium with drying times of 83, 38, 29, and 17 h at drying temperatures of 40, 50, 60, and 70 °C, respectively. The Page model fantastically described the drying process of mulberries. The transverse relaxation time (T2) curves showed that T2 times of free water decreased to the equilibrium points corresponded exactly with the first stage of drying kinetic curves. MRI showed that water diffused from the internal to the external during drying. Optimum color, texture, microstructure and higher total anthocyanin content were found in mulberries dried at 50 °C. Notably, higher correlations between LF-NMR parameters and quality properties were found by partial least squares regression (PLSR), with the analysis results being credible.