Effect of Drying Parameters on Drying Characteristics and Forskolin Content of Rotary Dried Coleus

Abstract

Coleus (Coleus forskohli), a medicinal crop, contains a bioactive component forskolin, which is extracted and used in several ayurvedic medicines in India. Drying is the primary operation to extract forskolin. In this the study, Coleus was dried in a rotary drier by varying slice thickness (2.5, 5.0, 7.5 mm), drying air temperature (45, 55, 65 o C), and feed volume (50, 60, 70 percent); and the forskolin contents were assessed. The moisture content reduced to 16.55% (d.b.) from 464.97% (d.b.) after rotary drying. The drying time ranged from 300 min to 450 min. The effective moisture diffusivity and activation energy ranged from 1.02 ×10-7 mm2 .s-1 to 1.33 ×10-6 mm2 .s-1 and 5.39 kJ.mol-1 to 15.57 kJ.mol-1, respectively. Forskolin content in dried root varied from 0.14% to 1.87 per cent. High forskolin content was found in 2.5 mm thick slice dried at 55 o C and 70% feed volume. Analysis of variance showed that forskolin content in dried Coleus root was significantly (p<0.0001) affected by slice thickness and drying air temperature than feed volume (p<0.01).