Comparison of different extraction techniques for isolation of antioxidants from sweet grass (Hierochloë odorata)

Strong antioxidants, 5,8-dihydroxycoumarin and 5-hydroxy-8-O-β-d-glucopyranosyl-benzopyranone were extracted from sweet grass (Hierochloë odorata L.) by using Soxhlet (SE), microwave-assisted (MAE) and supercritical fluid carbon dioxide (SFE) extractions at different extraction schemes and parameters. One-step MAE gave the most concentrated extract with 8.15% of 5,8-dihydroxycoumarin (extract yield 0.42%). Comparable results were obtained by one-step SFE and Soxhlet extraction. A two-step extraction was applied in order to increase the concentration of active compounds. Taking into account antioxidant recovery and concentration as well the extraction time and environmental aspects, two-step SFE was considered as a preferable method. The obtained crude extract contained 20.31% of 5,8-dihydroxycoumarin and 2.18% of 5-hydroxy-8-O-β-d-glucopyranosyl-benzopyranone. The extraction yields were 0.46 and 0.06%, respectively. First-step of SFE extraction was performed from dried herb at 35 MPa and 40 °C with 20% of ethanol as a modifier; the second extraction step was performed from the crude extract at 25 MPa and 40 °C.