Standardization of post-harvest technology for Gymnema sylvestre and Plectranthus forskohlii (Wild) Briq (Syn: Coleus forskohlii)
S. Padmapriya, K. Rajamani
Experiments were conducted at Medicinal Plants Unit, Horticultural College and Research Institute, Coimbatore to standardize the drying and storage technology for gymnema and medicinal coleus. The leaves of Gymnema were subjected to different drying treatments viz., sun drying, shade drying, initial sun drying and subsequent shade drying and shade drying followed by sun drying. Likewise, the harvested tubers of Coleus were cut into slice of different thickness (0.5, 1.0 and 2.0 cm) and dried in two methods viz., sun drying and mechanical drying. Observations were recorded on drying time, drying rate and alkaloid contents in both the crops. In gymnema, drying under open sun light took the lowest time for drying ie., 14 hrs/300g, followed by, shade drying followed by sun drying (20 hrs) and sun drying followed by shade drying (28 hrs). While drying the Gymnema leaves under shade required longer time (32 hrs) than other methods. The highest drying rate was observed in sun drying (0.276g/min) method. The highest gymnemic acid content (344.25 mg 100g-1) was recorded in shade dried leaves. In coleus, sun drying of 0.5 cm slice thickness registered 18 hrs for attaining 8% moisture level. While in mechanical drying method, drying at 60oC of 0.5cm slice tubers took the lowest time for drying ie. 360 min/100g with a drying rate of 0.370 g/min. The drying rate was found to be the lowest in sun drying of 2cm slice with a value of 0.065 g/min. The highest forskolin content (0.68%) was recorded in mechanical drying of 0.5 cm slice thickness at 40 °C. Storage studies indicated that irrespective of the crop under study, the dried sample packed in polyethylene lined gunny bag retained the highest alkaloid content and the rapid deterioration was recorded when stored under ambient conditions.