Investigation of microwave application time with constant pulse ratio on drying of zucchini.

Since nonuniform drying in the continuous microwave harms the safety and quality of dried food materials, a significant quality improvement can be achieved by controlling the application time of the microwave. This study aimed to investigate the influence of microwave application time and power at a constant pulse ratio during the drying of zucchini on different product characteristics. The samples were first exposed to microwaves with powers of 360, 600, and 900 W alternately for 10, 30, and 50 s. After drying with intermittent microwaves, the process was continued using the hot-air drying. Increasing the microwave application time and power caused a significant reduction in the total process time. The minimum drying time was obtained at 900 W and 50 s (259.44 min). D increased significantly by 24.4% and 34.1% with increasing application time and power, respectively. The highest shrinkage and bulk density were observed in the samples dried at 360 W and 10 s due to a longer total process time than the other treatments. Rehydration increased by 10.3% and 14.7% with increasing application time and power, respectively. A 33% decrease in energy consumption was noticed in the 900 W-50 s treatment compared to the 360 W-10 s treatment. Moreover, with increasing microwave application time and power, the lightness of the dried product decreased, and the total color difference increased. In summary, the 900 W power and 50 s application time produced a better-dried product than the other treatments considering different quantitative and qualitative properties. The results of this research can be used in the food industry to dry products using microwave and hot air to control and improve their quality.