Extraction of phytochemicals from switchgrass using hot water

Switchgrass (Panicum virgatum L.) is receiving significant attention as a feedstock for the production of liquid fuels such as ethanol. In addition, switchgrass may also be a source of value-added products such as antioxidants and our laboratory recently reported that switchgrass contains policosanols and alpha-tocopherol. A sample of the switchgrass variety, Cave-in-Rock, was obtained from the September-October harvests in Fayetteville, Arkansas and extracted with water at 50°C. The extracts were freeze-dried and then dissolved in dimethyl sulfoxide (DMSO) and tested for Low Density Lipoprotein (LDL) oxidation inhibition activity using the Thiobarbituric Acid Reactive Substances (TBARS) assay. TBARS results showed that the extracts inhibited LDL oxidation by as much as 60% in comparison to controls without extracts. Liquid chromatography coupled with mass spectrometry (LC-MS) and high performance liquid chromatography (HPLC) were used to identify the compounds in the water extract that are likely responsible for the LDL oxidation inhibition activity as flavonoids, quercitrin (quercetin-3-O-rhamnoside) and rutin (quercetin-3-O-rutinoside). Water and 60% methanol extracts of switchgrass at different temperatures were analyzed for their flavonoid content. With 60% methanol treatment, rutin concentrations in the extracts were in the range of 502 to 670 mg/kg, while those of quercitrin varied between 554 and 732 mg/kg. On the other hand, with liquid hot water, the rutin concentrations were in the range of 82 mg/kg to 185 mg/kg, while those of quercitrin were 37 mg/kg to 193 mg/kg. Centrifugal partition chromatography (CPC) was used to separate rutin and quercitrin in the switchgrass water extract, which showed lipid peroxidation inhibition activity.