Effects of extraction solvents on total phenolic and flavonoid contents and biological activities of extracts from Sudanese medicinal plants

Solvents used during extraction process are reported to have an influence on the nature and the amount of secondary metabolites extracted from medicinal plants. Thus, the choice of proper extraction solvent is necessary for the desired pharmacological activity of these extracts. In the present study, we extracted six medicinal plants grown in Sudan, namely, Blepharis linariifolia, Cyperus rotundus, Guiera senegalensis, Maerua pseudopetalosa, Tinospora bakis and Dicoma tomentosa with six solvents of different polarity, i.e. water, 50% ethanol (EtOH), 70% EtOH, 95% EtOH, acetone and dichloromethane to obtain total 36 extracts. Quantitative estimation of total phenolic and flavonoid contents was performed. These extracts were further evaluated for their free radical scavenging activities and α-glucosidase, pancreatic lipase and tyrosinase inhibitory activities. 50% EtOH and 70% EtOH extracts of G. senegalensis showed the highest content of phenolic compounds in comparison to other extracts. For total flavonoid contents, higher content was found in acetone extracts of G. senegalensis followed by B. linariifolia and M. pseudopetalosa. Polar extracts showed higher free radical scavenging activity in comparison to dichloromethane extract, with 70% EtOH and 50% EtOH extracts of G. senegalensis being the most active ones. The 50% EtOH and 70% EtOH extracts G. senegalensis also showed the potent inhibitory activity against α-glucosidase. In contrast, acetone and dichloromethane extracts showed potent pancreatic lipase inhibitory activity. Potent tyrosinase inhibitory activity was shown by acetone extract of G. senegalensis. In conclusion, 50% EtOH, 70% EtOH and acetone were found to be the best solvents of choice for the extraction of phenolic compound rich extracts with free radical scavenging and enzyme inhibitory activities. Further studies should focus on the isolation and identification of active secondary metabolites from these extracts.