Effect of air temperature and velocity on the drying characteristics and product quality of Clinacanthus nutans in heat pump dryer

Abstract

Fresh Clinacanthus nutans (C. nutans) leaves were dried using a heat pump dryer where the effects of drying temperature (40, 50, and 60°C) and air velocity (2.5, 3.0, and 3.5 m/s) on the drying characteristics and product quality were investigated. Data showed that higher air temperature and velocity resulted in a shorter drying duration. At higher air temperature and velocity, more heat was supplied to the C. nutans leaves, which increased the drying force for moisture evaporation and subsequently led to faster drying rate. The drying kinetics were best fitted with Midilli et al. model (R 2 = 0.9556). The quality analysis revealed that vitexin and orietin contents were preserved at varied extent depending on the drying temperature and duration. The highest preservation of vitamin C and total colour change was achieved at drying conditions of 50 °C (3.5 ms-1) with 90.7 % and 94.6 % maintained, respectively. This was because the pigment colours and vitamin C were easily degraded if the products were exposed to excessive heat (high temperature) and prolonged drying process (time taken). Overall, heat pump dryer presented a short drying duration without compromising the product quality for the drying of C. nutans. Heat pump dryer can be used to extend the shelf life of C. nutans and increase the commercialization potential and wide use of C. nutans.