Antioxidant properties and involved compounds of daylily flowers in relation to maturity

The antioxidant properties of methanol extracts from daylily flowers during maturation were determined with antioxidant assays, including antioxidant activity, DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging, superoxide anion radical scavenging and reducing power. Antioxidant compounds, such as phenolic compounds, ascorbic acid and β-carotene were also analysed. Significant variation in antioxidant properties and involved compounds was observed between different maturity stages of daylily flowers. The highest antioxidant activity was observed at stage III (flower opening) accompanying the highest content of ascorbic acid and phenolic compounds, while no significant difference of β-carotene contents was observed among the four maturity stages. Four individual phenolics, such as (+)-catechin, chlorogenic acid, rutin and quercetin were identified and quantified by HPLC. (+)-Catechin was the main phenolic compound identified in daylily flowers, accounting for about 74.11% of total phenolics. Overall, daylily flowers at opening stage possess the highest functional benefit and thus would be the appropriate harvesting stage in view of the nutritional consideration.