Abstract:
The leaf extracts of Gymnema sylvestre consist of secondary metabolites which are well
known for antioxidant activity. This study aimed to measure the drying characteristics of G. sylvestre
leaves under far-infrared radiation (FIR) and to optimize the specific energy consumption for drying
and antioxidant activity of ethanol-water extract of dried leaves. Fresh leaves were harvested and
exposed to combinations of four different temperatures (125, 150, 175 and 200 ◦C) and exposure
times (5, 10, 15 and 20 min). Drying kinetics, energy consumption, color changes, total phenolic
content (TPC) and antioxidant activities were quantified. Both temperature and drying time have
significant (p < 0.05) effects on drying characteristics and antioxidant activity. The equilibrium
moisture content was achieved at 200 ◦C and 18 min. The specific energy decreased and total
color changes increased with temperature. Under lower temperatures (125 and 150 ◦C), TPC and
antioxidant activity increased with exposure time, whereas higher exposure time (20 min) with high
temperatures (175 and 200 ◦C) significantly decreased TPC and antioxidant activity. The highest
TPC of 30.5 mg TAE/g leaf-fresh weight was achieved at 200 ◦C and 15 min. The optimal drying
conditions achieved from the dissimilarity function method were 200 ◦C and 8.4 min.
