Abstract:

The aim of the present study was to investigate the drying characteristics of onion under varying microwave powers. The results showed that much shorter length of time was required for microwave drying when compared to hot air drying. The lengths of time required for microwave drying at 119 W and 231 W powers were 0.35 times and 0.125 times shorter than those required for hot air drying at 80 ℃. Under the condition of microwave power 383 W, onion began to become brown. Under the condition of microwave power above 385 W, increasing microwave power could result in more serious brown of onion. However, under the conditions of 119 W and 231 W, brown phenomena rarely occurred. In addition, the rehydration ratios of onion under 119 W and 231 W were 4.87 and 4.67, respectively, higher than those under other microwave powers. The microwave drying of onion proved to be a constant speed process and its mathematical model was in line with Page equation.

Key words: onion, microwave drying, drying characteristics, mathematical model, quality