2.8. Antioxidant Activity of RO

The antioxidant properties of RO (0.5 mg/mL) and RO nanoliposomes (0.5 mg/mL) were characterized by DPPH and the ABTS radical-scavenging activity, and were detected in triplicate. The DPPH radical-scavenging activity of RO and RO nanoliposomes were measured using the method of Sarabandi et al. [35], with slight modifications. 2 mLnanoliposome samples were mixed with 2 mL of 0.1 mM DPPH solution prepared in ethanol. The mixture was then vortexed and kept for 30 min in a dark place. Then, the absorbance of the mixture was measured at 517 nm, and was calculated using the following Equation (2):

The ABTS radical-scavenging activity of RO and RO nanoliposomes were measured referring to the method of Shishir et al. [36], with slight modifications. First, 2 mL of 7 mmol ABTS solution was combined with the same volume of 2.45 mmol potassium persulfate. The solution mixture was incubated in the dark for 12–16 h at room temperature. Before the test, 1 mL of the solution mixture was diluted with ethanol to obtain an absorbance rate of 0.70 ± 0.02 at 734 nm. Then, 3800 µL test mixture solution was added in 200 µL of nanoliposomes, reacted in the dark for 30 min, and measured at 734 nm. Then, the ABTS of RO and RO nanoliposomes were calculated from the following Equation (3):