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In the present study, the influence of drying temperature on energy consumption and qualitative characteristics of onion including rehydration capacity, vitamin C content and total phenolic content (TPC) was investigated. Onion slices with 3 mm thickness was dried in a hot air dryer at temperatures 0f 40‒70 °C. Specific energy consumption and energy efficiency were significantly (P < 0.05) improved by increasing temperature and obtained to be in the range of 35.83‒59.33 MJ/kg and 4.01‒6.52%, respectively. Increasing air temperature resulted in significant (p < 0.05) improvement in energy consumption indices. Rehydration capacity in the dried onion samples varied from 4.01% (at drying temperature of 40 °C) to 6.52 (at drying temperature of 70 °C). Vitamin C content in fresh samples was 50.19, and in dried samples varied from 14.92 to 21.38 mg/100 g _{dry matter}. TPC was measured using Foline–Ciocalteu reagent and found that the TPC in fresh onions (389.6 mg GAE/100 _{dry matter}) was significantly (p < 0.05) decreased in the dried samples (212.3‒295.8 mg GAE/100 _{dry matter}). Based on the obtained results, drying of the onions at higher temperatures led to more deterioration in vitamin C content and the TPC.

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In the present research, microwave drying process of potato slices were thermodynamically analyzed and evaluated. During the experiments, potato slices with thicknesses of 3.5, 5, 7 and 9 mm were dried using powers of 200, 400, 600 and 800 W. Specific energy consumption was obtained to be the range of 0.83‒3.29 MJ kg^-1, and significantly increased (p < 0.05) with increasing samples thickness. Energy efficiency of the process (13.23‒35.59) was significantly (p < 0.05) improved with increasing microwave power and decreasing samples thickness. Average specific energy loss of the process varied from 0.69 to 2.71 MJ kg^-1. Exergy efficiency and sustainability index of the process changed from 10.03 to 28.17 % and from 1.11 to 1.39, respectively. In General, according to the results obtained in this research, practicing higher microwave powers to dry thinner samples improved the thermodynamical performance and reduced the environmental footprints of the process.