An efficient microwave-assisted extraction of anthraquinones from Rheum emodi: Optimisation using RSM, UV and HPLC analysis and antioxidant studies

Rheum emodi a culinary plant used across the world, is known to contain bioactive anthraquinoids which find extensive use in the chemical, pharmaceutical and cosmetic industry and exhibit diverse pharmacological actions. The current work envisages development of a microwave assisted extraction (MAE) for extraction of total anthraquinones (AQs) and five 1,8-dihydroxyanthraquinones (DHAQs) from Rheum emodi. In the initial part of the work, a rapid and facile method was developed for determining total AQs using UV spectroscopy. Preliminary screening experiments were performed to select choice of solvent, extraction time, microwave power and solvent: sample ratio. Subsequently, optimum conditions for MAE were determined using RSM by employing a Box-Behnken design. Extraction rate of total AQs and five DHAQs reached maximum at time 7.5 min, microwave power 490W, solvent: sample ratio 15: 0.1 ml/g and concentration of aqueous NaOH solution 0.255 M. Furthermore, MAE offered significantly higher yields for total AQs and five DHAQs and also a high DPPH-scavenging and hydrogen peroxide scavenging potential than the extracts obtained by conventional extraction methods. The proposed method was fast, energy-saving, environment-friendly and can find a potential industrial use in the extraction of the bioactive DHAQs. (C) 2015 Elsevier B.V. All rights reserved.