Switchgrass Water Extracts: Extraction, Separation and Biological Activity of Rutin and Quercitrin

Switchgrass (Panicum virgatum L.) has recently received significant attention as a possible feedstock for the production of liquid fuels such as ethanol. In addition, switchgrass may also be a source of valuable co-products, such as antioxidants, and our laboratory recently reported that switchgrass contains policosanols and α-tocopherol. Motivation for this work began when a switchgrass sample was extracted with water at 50 °C and was then tested for low-density lipoprotein (LDL) oxidation inhibition activity using the Thiobarbituric Acid Reactive Substances (TBARS) assay. The TBARS results showed that the switchgrass water extracts inhibited LDL oxidation by as much as 70% in comparison to the control. Liquid chromatography coupled with mass spectrometry (LC-MS) and high performance liquid chromatography (HPLC) were used to identify the compounds that were responsible for LDL oxidation inhibition activity as flavonoids: quercitrin (quercetin-3-O-rhamnoside) and rutin (quercetin-3-O-rutinoside). To maximize flavonoid concentrations, switchgrass was then extracted with water and 60% methanol at different temperatures. The 60% methanol treatment resulted in higher rutin and quercitrin yields when compared to water-only extraction; however, the use of this solvent would not be practical with current biorefinery technology. Centrifugal partition chromatography (CPC) was then used to purify rutin and quercitrin from the switchgrass water extract, which were then tested via the TBARS assay and shown to exhibit lipid peroxidation inhibition activity similar to that obtained with pure flavonoid standards. This is the first report on the presence of rutin and quercitrin in switchgrass. The results support the extraction of viable coproducts from switchgrass prior to conversion to liquid fuel.