Free radical scavenging activity (DPPH assay)
The 2, 2-Diphenyl-1-picrylhydrazyl (DPPH) assay was used to determine the free radical scavenging activity of cur@star according to the previous report (Kim et al., 2008). DPPH working solution was prepared by dissolving DPPH reagent in ethanol at the concentration of 0.1 mM. To 4 mL of the above working solution, 1 mL of curcumin ethanoic solution or sample water solutionwas added. The mixture was shaken and left in the dark at room temperature for 30 min. Absorption at 517 nm was recorded on a UVevis spectrophotometer. DPPH radical scavenging activity was estimated according to the following equation: