Developing an effective pretreatment process for hot-air drying of Chinese yam (Dioscorea opposita Thunb.) slices: Drying characteristics, efficiency, and quality.

This study evaluated the effects of both thermal (microwave, hot water, steam) and non-thermal (cold plasma, ultra-high pressure) pretreatments of Chinese yam. The results showed that the time of hot-air drying 70 °C was shortened by 20.83 %, 13.89 %, 2.78 %, 8.33 %, and 16.67 %, respectively, after pretreating with microwave (560 W, 90 s), hot water (70 °C, 3 min), steam (120 °C, 2 min), cold plasma (6 cm, 6 min), and ultra-high pressure (300 MPa, 8 min). Microwave pretreatment exhibited the highest drying rate, water diffusion coefficient (D), elasticity, and cohesion. In particular, microwave pretreatment reduced the free water content from 69.17 % to 23.08 % in samples, and induced the formation of small, uniform pores that brought about a distinct honeycomb microstructure. The drying kinetics of microwave-pretreated samples were best fitted by the Midilli et al. model. Microwave pretreatment is a promising strategy to improve the drying efficiency and quality of yam slices.