Abstract
Moringa oleifera leaves were dried in a domestic microwave oven to investigate the influence of microwave power levels on rate of drying, drying time, the quality of the dried product based on their colour, protein, and iron content as well as the energy consumption. Four different microwave power levels varying from 300 to 1,000 W were selected in the experiments. Drying time increased significantly with the decrease in microwave output power. At 1,000, 800, 500 and 300 W the drying time were 6, 8, 10 and 20 min. The initial drying rate was very fast at all power levels as the penetration of microwave power were applied throughout the leaves. All microwave power levels showed a drying rate in a decreasing trend as the falling rate was observed at the point when the moisture content (MC) started to reach below 5 %. Throughout the drying progression, the drop in the product moisture caused a decrease in the absorption of microwave power and leads to a fall in the drying rate. For the changes in the colour, there was a significant difference in the value for greenness (-a), but no notable differences were observed between the colour parameters of fresh and microwave-dried leaves for whiteness L value, yellowness b and hue angle. This indicates that drying under a microwave oven darken the leaves, yet the colour retained its original values similar to the fresh M. oleifera leaves. There was no significant difference in the value for protein but a significant difference in the value for iron contents of the fresh and microwave-dried leaves (P<0.05). The highest energy consumption was recorded at 1,000 W with 0.154 kWh and the lowest at 500 W with 0.117 kWh. Results from this experiment reveal a great alternative for the microwave oven method on M. oleifera leaves as a rapid drying method.
