Abstract :
Parsley (Petroslinum crispum Mill.) leaves were dried in a domestic microwave oven to determine the effects of microwave output power on drying time, drying rate and the dried product quality in terms of colour. Seven different microwave output powers ranging from 360 to 900 W were used in the drying experiments. Drying took place mainly in constant rate and falling rate periods. After a short heating period a relatively long constant rate period was observed. Approximately 40·5% of the water was removed in this period. The rapidly decreasing falling rate period followed the constant rate period. As the drying progressed, the loss of moisture in the product caused a decrease in the absorption of microwave power and resulted in a fall in the drying rate. Increasing the microwave output power resulted in a considerable decrease in drying time (probability P<0·01). The semi-empirical Pageʹs equation used to describe the drying kinetics of dried leaf materials gave an excellent fit for all data points with values for the coefficient of determination R2 of greater than 0·997 and for the standard error of estimates (SEE) of lower than 0·0188. The value of the drying constant increased with increased microwave output power. No significant differences were observed between the colour parameters of fresh and microwave-dried leaf materials, except for some decrease in whiteness L value (P>0·05). The change in colour values was not dependent on the microwave output power. Although some darkening occurred, microwave drying maintained a good green colour close to that of the original fresh parsley leaves. By working at 900 W instead of 360 W, the drying time could be reduced by 64% with a good quality product.
