Effects of hot air and microwave-assisted drying on drying kinetics, physicochemical properties, and energy consumption of chrysanthemum

For this study the chrysanthemum was dried using hot air at temperatures of 45, 75, and 105 degrees C (H1, H2, and H3), as well as microwave (30, 60, and 90 s) combined with hot air at temperature of 75 degrees C (MH1, MH2, and MH3). The highest effective diffusivities (16.23 x 10(-9)) and the lowest (5.37 x 10(-9)) belonged to MH3 and H1, respectively. The activation energy for hot air drying was calculated to be 18.40 kJ mol(-1). Eleven mathematical models were fitted into the experimental data. The Midilli model was the appropriate simulation for the drying processing of H1, H3, and MH2. The Diffision Approach and Two Term models were both the reasonable models describing the drying behavior of MH1 and MH3. The shrinkage and rehydration capacity were raised with increasing temperature and microwave time. The contents of total phenolics, total flavonoids, and seven monomeric compounds, as well as the results of Fourier transform infrared (FTIR) indicated that MH1 contained the higher content of active principle, and little changes in entire conformation. Specific energy consumption for hot air drying and combined drying was ranged from 92.0 to 135.1 kW h kg(-1), and from 112.4 to 1289.6 kW h kg(-1), respectively.