摘要
In this research, convective and microwave drying characteristics, energy requirement and color changes of dill leaves （Anethum graveolens L.） were reported. Dill leaves were dehydrated in a computer connected parallel air flow type dryer and in a microwave oven dryer. Samples of freshly harvested dill leaves were dehydrated under three air temperatures of 50, 60 and 70 ℃, and at three microwave power levels of PL-1 （90 W）, PL-2 （160 W） and PL-3 （350 W）. Selected drying air velocity was 0.30 m/s for all temperatures. Dill leaves were dehydrated from the initial moisture content of 735 （percentage dry basis） to a final moisture content of 8%-10%. During convective drying experiment, products were weighted automatically by the balance per 5-10 min. Data were transferred to the computer and processed by software. During microwave drying, the products were weighted, and data were recorded manually per 15-60 min. The influence of drying method, drying air temperature and microwave power level has also been studied. Hunter L, a, b values system was also used to evaluate changes in total color difference （AE） on dried products. The results showed that convective drying air temperature and microwave oven power levels influenced the total drying time, total energy requirement, specific energy requirement and color difference for dill leaves. The minimum specific energy requirement was determined as 10.72 kWh/kg and 18.72 kWh/kg for 70 ℃ and PL-3, respectively. 70℃ drying air temperature and PL-3 were found to yield better quality product in terms of color retention of Hunter L, a, b and AE. As a result, to reduce drying energy consumption and to keep better color retention, convective drying can be recommended for this application.
