DPPH radicals scavenging ability detection
The assay was performed according to the previous study (Weng et al., 2019) with some modifications. Samples of CA, FA, p -HCA, CG, FG and p -HCG were dissolved in anhydrous ethanol at different concentrations (1.0, 0.5, 0.25, 0.125, 0.0625 mM). DPPH was dissolved in anhydrous ethanol to make a solution with a concentration of 1.0 mM. Equal amounts of DPPH and sample solutions were mixed and then monitored spectrophotometrically at 517 nm using the UV-Vis spectrophotometer after standing for 30 min. Instead of antioxidant solution, anhydrous ethanol was used in the control groups. All the samples and reagents were freshly prepared daily. The corresponding inhibition percentages were calculated according to the following Eq.(2):