Characteristics of combined hot-air and microwave drying for sweet potato slice and quality evaluation

The characteristics of combined hot-air and microwave drying for sweet potato slice was studied,and the color,rehydration ratio,drying time and energy consumption of dried samples were evaluated. The results showed that : hot- air drying( HD) process and microwave drying( MD) process of combined hot- air and microwave drying(HD-MD) were both divided into accelerated drying stage and falling rate drying stage. MD process of combined microwave and hot-air drying(MD-HD) was divided into accelerated drying stage,constant rate drying stage and falling rate drying stage and HD process included falling rate drying stage only.The best model for describing HD process in combined drying was Verma and the best models for describing MD processes in HD-MD and MD-HD were Logarithmic and Page,respectively. L* value,a* value and b*value of dried samples obtained by HD-MD were 72.86 ±2.29,11.02 ±2.73 and 38.65 ±4.45,respectively. The dried samples didn 't brown seriously and β-carotene was reserved better. Rehydration ratio,drying time and energy consumption of samples obtained by HD-MD were(2.17±0.03),(104±4.93) min and(18.71±1.05) k W·h/kg,respectively. Compared with HD,drying time of HD-MD was shortened by 55% and energy consumption was reduced by 64%. HD-MD was more suitable for drying of sweet potato slice with good quality of products and low energy consumption.