Optimisation of harvesting time and drying techniques for higher sennosides in Cassia angustifolia Vahl. by RP-HPLC

Abstract

The commercially important leaves and pods of senna (Cassia angustifolia Vahl.), have many medicinal uses, including laxative properties due to active compounds such as sennoside A (SA) and sennoside B (SB). The content of secondary metabolites in the plant depends on harvesting time (HT), plant parts, and post-harvest techniques, apart from soil and climate conditions. In the present report, a simple, efficient and improved Reverse Phase High Performance Liquid Chromatography (RP-HPLC) method for simultaneous quantification of sennosides (SA and SB) in different parts of C. angustifolia, harvested at 15 days short growth intervals was developed and used to optimise HT and drying techniques through monitoring the active compound content. An ideal HT for optimum content of sennosides in the leaf was observed at 90 days after sowing (DAS) (1.13%) and in pods at 105 DAS (1.4%). From the studies, the order of sennoside content range in different parts was: pods (1.21–1.4%) > leaves (0.25–1.19%) > whole plant (0.17–0.80%) > stem (0.16–0.74%) > root (0.06–0.14%) > flower (0.03–0.04%). These studies suggest that the discarded stems can also be considered for commercial exploitation. Further, different drying techniques revealed that on oven drying of leaves at 50 °C and 60 °C, more than 70% moisture loss within 6.4 h; in the p°ds, more than 77% moisture loss within 10 h was recorded. Shade drying and oven drying at 40 °C removed moisture, from leaves and pods, not more than 69% and 64%, respectively, even after 52 h. The RP-HPLC results showed that the leaves dried in the oven at 50 °C and pods dried at 40 °C possessed the highest sennosides content (1.28% and 3.21%, respectively). Sennoside content increased tremendously by 61.2% in the pods and 16.3% in the leaves when oven-dried at 40 °C and 50 °C, respectively, compared with shade drying. The present optimisation studies revealed that senna leaves harvested during 90–105 DAS and dried in the oven at 50 °C, pods harvested at 105 DAS and dried at 40 °C produced higher content of sennosides.