Chiang Mai Journal of Science

      Drying is an essential process for preserving agricultural products. Most natural biological compounds are sensitive and easily degraded under drying conditions. This study investigated the effects of drying temperature (40, 50, 60, and 70°C), air velocity (0.05, 0.10, 0.15, and 0.20 m/s), and feed amount (0.60, 0.80, 1.00, and 1.30 kg/m²) on the moisture ratio, drying rate, mitragynine (MG) content, and specific energy consumption (SEC) of kratom leaves. The results showed that temperature, air velocity, and the quantity of kratom leaves significantly affected the drying process. The drying kinetics of kratom leaves were best explained by the Midilli-Kucuk model. The R², reduced χ², SSE, and RMSE values of the Midilli-Kucuk model under hot air drying varied from 0.9965 to 0.9993, 0.000075 to 0.000358, 0.001124 to 0.007869, and 0.007692 to 0.01740, respectively, for kratom leaves dried at 40, 50, 60, and 70°C. The MG content of dried kratom leaves at 40°C was the highest at 10.10 mg/g. The lowest SEC values, which corresponded to the highest amount of MG in the dried leaves, were achieved at a drying temperature of 40°C, an air velocity of 0.2 m/s, and a kratom leaves feed amount of 0.60 kg/m2.