Flavonols of lotus (Nelumbo nucifera, Gaertn.) seed epicarp and their antioxidant potential

Large amounts of fresh seed epicarp of Nelumbo nucifera Gaertn. (FSENN) are discarded in China without any utilization. The aim of this study was to identify the flavonols found in a fraction of an extract of FSENN, and to measure their levels and investigate antioxidant properties. Glycosylated flavonols in fraction 2 (Fr2) from the extract of FSENN and their aglycones were identified by HPLC-ESI–MS2 (negative mode), and six glycosylated and one aglycone flavonols in Fr2 were found. We also quantified flavonol aglycones (myricetin, quercetin, kaempferol and isorhamnetin) using HPLC method. The result showed that the quercetin content (10.2 mg/g of dry fraction) was higher than that of other aglycones. Antioxidant properties of Fr2 were evaluated in vitro by a number of methods including 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, the β-carotene bleaching method, and hydroxyl radical and hydrogen peroxide scavenging ability using the chemiluminescence method. This antioxidant potential in terms of IC50 values was 5.48, 40 ± 0.14 and 0.62 ± 0.05 μg (dry Fr2)/mL on DPPH radicals, hydroxyl radicals and hydrogen peroxide, respectively. The Fr2 also exhibited antioxidant property in the β-carotene bleaching assay. In total, it possesses high levels of flavonol compounds with high antioxidant potential, and it is beneficial for the treatment or prevention of a variety of diseases and has nutraceutical potential.