In order to obtain the optimal technological parameters of lettuce vacuum osmotic dehydration, the effects of osmotic temperature, slice thickness, sucrose concentration, and vacuum degree on the vacuum osmotic dehydration were explored. The lettuce water loss rate and solid gain rate decreased with the increase of slice thickness and vacuum degree, and increased with the increase of sucrose concentration and osmotic temperature. Response surface methodology was applied to analyze the influence of the four influential factors on the evaluated parameters and the optimization of lettuce vacuum osmotic dehydration was studied. The results indicated that, within the experimental scope, the optimized technological parameters of lettuce vacuum osmotic dehydration are the temperature of 28°C, the slice thickness of 2 mm, sucrose concentration of 47%, the vacuum degree of 22 kPa, and the water loss rate and solid gain rate are 72.16% and 11.82%, respectively.

Aiming at the problem of multilayer physical structure for the skeleton of porous media, a multiscale and multilayer structural model of heat and mass transfer processes for drying of grain packing porous media was established by applying the pore network method and multiscale theory. An experimental study on rice drying was conducted in order to validate this model. The simulation and experimental results indicated that the established model could explain the mechanical properties of rice drying well. The rate of heat transfer was faster than the rate of mass transfer and there was a higher moisture gradient inside the rice grain. The diffusion coefficient of rice embryo played an important role in the drying process, and whose effect on drying was larger than the diffusion coefficient of rice hull and chaff. The moisture was imprisoned effectively inside the rice when the diffusion coefficient of rice embryo was very small.

This study compared four drying methods, namely hot-air and vacuum combined drying (HAVCD), hot-air drying (HAD), vacuum drying (VD), and vacuum freeze-drying (VFD), with the aim to select a high-quality and efficient drying method to dry American ginseng slices. Drying kinetics and various physicochemical properties, such as color, rehydration ratio, total ginsenoside content, total ginsenoside residual rate, hardness, and microstructure were explored. An improved multi-indicator test formula method was used to score the experimental results quantitatively. HAVCD resulted in comprehensive advantages, with the highest product score for the dried American ginseng slices. Therefore, HAVCD was subjected to a response surface methodology (RSM) analysis and process optimization. The interaction of hot-air temperature and vacuum temperature on the comprehensive score of American ginseng drying was highly significant (p < 0.01). The optimized and validated process parameters obtained were a hot-air temperature of 57 °C, a vacuum temperature of 54 °C, and a moisture content at the conversion point of 39% (wet basis). Under these conditions, the best drying time was 170 min; the total ginsenoside content was 2.3 mg/100 g; the L* value was 91.68; the rehydration ratio was 3.10; and the comprehensive score was 96.77. The findings of this work indicated HAVCD as a promising drying method for American ginseng slices, considering the drying time and dried-product quality attributes.