Biorefining of Cymbopogon nardus from Reunion Island into essential oil and antioxidant fractions by conventional and high pressure extraction methods

Steam distilled essential oil of Cymbopogon nardus has been widely studied and commercialized; however, comprehensive valorisation of plant material requires more systematic characterization of other, non-volatile extracts and their potential activities. For this purpose C. nardus herb was fractionated into essential oil (EO) and non-volatile fractions by hydrodistillation (HD), Soxhlet (S), supercritical CO2 (SFE-CO2) and pressurized liquid (PLE) extractions. Antioxidant potential was evaluated by total phenolics (TPC), DPPH center dot/ABTS(center dot+) scavenging and oxygen radical absorbance (ORAC) capacity. The yields were from 1.37/1.39% for SFE-CO2 (50 degrees C)/HD to 12.2/12.6% (w/w) for PLE-water/freeze dried after EO-HD water (PLE-WE/FD-WE). TPC was higher in S-acetone (S-AE) and PLE-WE, 70 and 60 mg of gallic acid equivalents (GAE)/g dew (dry extract weight), respectively. S-AE and S-ethanol extracts were strongest antioxidants, on average equivalent to 770 mu mol of trolox equivalents (TE)/g dew in ABTS assay. Antibacterial activity was tested by well agar diffusion and minimal inhibitory concentration (MIC) methods with various microorganisms; EO at 3% inhibited all bacteria, except for S. aureus and S. typhimurium; MICs were in the range of 0.39-12.5 mg/mL. C. nardus extracts may be considered as potential natural antioxidants and antibacterial agents and a good source of phenolics.