Drying Schinus terebinthifolius leaves in a rotating drum dryer – Evaluation of the product quality and energy consumption by RSM models

The performance of a specially designed rotating drum for processing medicinal leaves was evaluated for air drying Schinus terebinthifolius leaves. The study is aimed at investigating the influence of air temperature, air velocity, leaf mass load, and drum rotation speed on leaf drying. Response Surface Methodology (RSM) was employed to optimize the drying conditions. Second-order polynomial equations were used to assess the effects of drying conditions on drying time, color degradation, and energy consumption. Based on the analysis, the optimum drying conditions were determined to be an air temperature of 52.5 °C, air velocity of 0.3 m/s, and a mass load of 200 g. The predicted values of drying time, specific power input and the chromatic parameter a*/b* at this optimal condition were 499 min, 14.4 kWh/kg and − 0.063, respectively. Furthermore, a comparison between ethanolic extracts obtained from fresh leaves and those from dried leaves revealed a significant decrease in total phenolic compounds (TPC) and antioxidant activity (AA) in the extracts from the dried leaves. Among the tested conditions, the best result for both TPC and AA was observed in the extracts of leaves air dried under 50 °C and 0.60 m/s, in which the TPC and AA dropped respectively from 75 mg GAE/mg dry matter and 90 % to approximately 22 mg GAE/mg dry matter and 88 %. The air temperature was identified as the most influential factor affecting the quality attributes of dried leaves and their extracts. The rotating drum proved to be an effective alternative for drying herbs and medicinal leaves.