Drying Characteristics and Kinetics of Individual Lotus Seeds under Hot Air drying Process
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Abstract:
In order to improve the quality of dried lotus seed, shorten the drying time, and reduce energy consumption, hot air drying processes at constant temperatures (50~90 ℃) and stepwise varying temperatures (60~80 ℃) were adopted to dry individual lotus seeds. Changes in the appearance, rehydration characteristics, energy consumption, and drying characteristics of lotus seeds were investigated, and the effective diffusion coefficient and activation energy were calculated. The results indicated that when the lotus seeds were dried at constant temperatures, the drying time decreased with increasing air temperature, but the color, rehydration ratio, and other qualities deteriorated. When drying was conducted at stepwise varying temperatures, the drying time was shortened compared with that at a constant temperature of 60 ℃, and all qualities were improved. The rehydration ratio of lotus seeds dried using a stepwise varying temperature procedure of 60(3 h)~80 ℃ reached 169.41%, better than those of stepwise varying temperature processes of 60(2 h)~80 ℃ and 60(4 h)~80 ℃, and the unit energy consumption decreased from 14022 kJ/g to 11989 kJ/g compared with that of hot air drying at a constant temperature of 60 ℃. According to Fick’s second law, the effective diffusion coefficient of hot air drying at constant temperatures (50~90 ℃) ranges from 1.79×10-9 to 5.83×10-9 m2/s, and the average effective diffusion coefficient of hot air drying at stepwise varying temperatures ranged from 2.97×10-9 to 2.44×10-9 m2/s. The relationship between the effective diffusion coefficient and temperature was established using Arrhenius empirical formula, and the activation energy value of lotus seeds was calculated as 28.33 kJ/mol. The experimental results provide a valuable reference for the optimization of process parameters for drying lotus seeds and the design of drying equipment.
