Comparison of water mobility and distribution in Dioscorea opposita Thunb. cv. Tiegun during hot‐air and microwave drying processes

Abstract

SummaryLow‐field nuclear magnetic resonance (LF‐NMR) was employed to investigate changes in mobility as well as distribution of water in yam slices in the course of hot‐air drying (HAD) and microwave drying (MD) processes. Moisture content, effective moisture diffusivity, and water activity were also analysed. According to the results, a total of three water fractions with various T2 relaxation times were observed in fresh yam slices: T21 (0.9–2.6 ms), T22 (30–130 ms), and T23 (130–1245 ms). With the increment in drying temperature and the rise of microwave power in the course of drying, there was a significant decline in the transverse relaxation time and peak amplitude of T23. The overall moisture content exhibited a good correlation with Atotal during both HAD and MD processes, with coefficients equivalent to 0.9194 and 0.9024, respectively. With rising drying temperature and microwave power, there was a corresponding rise in effective moisture diffusivity. In comparison with HAD, the rate of water diffusion and evaporation in yam slices dried by MD was higher. Taking into account the drying efficiency and moisture state, MD was suggested as a preferable drying technology for dehydrating yam slices.