Potential use of low-field nuclear magnetic resonance to determine the drying characteristics and quality of Arctium lappa L. in hot-blast air

The present study investigated the effect of drying temperature (50, 60, 70, and 80 degrees C) on the drying kinetics and water properties of burdock slices. The changes in water mobility and water distribution were characterized using H-1 low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) techniques. The Page model satisfactorily described the hot-air drying curves of burdock. The drying kinetic curves showed that the second stage of drying corresponded exactly with when the relaxation times of free and immobile water decreased to the equilibrium points. MRI showed that water diffused from the center to the surface during drying. Overall, the LF-NMR, color and HPLC data showed that, at 60 degrees C, free water in burdock dissipated slowly, its color stability was higher, and its chlorogenic acid content was higher than at 70 and 80 degrees C. Significant correlations were found between moisture content, color and NMR parameters.