In vitro antioxidant studies of sweet potato leaves damaged by MW and HA. The third leaves of sweet potato plants were sampled at 0.25, 0.5 and 6 h after treatment with MW or HA. (A) The total phenolic content was measured at 725 nm and is expressed in gallic acid (GAE) equivalents; (B) The DPPH activity was measured at 517 nm using ascorbic acid as a standard, and the EC50 was calculated; (C) The SOD activity was measured at 560 nm and defined as the amount of enzyme that resulted in 50% NBT inhibition; (D-F) The catalase activity (D), POD activity (E) and H2O2 level (F) were measured using the TMB (3,3′,5,5′-tetramethylbenzidine) method. Data are means (±SE) of three independent experiments with three replicates. (* represents P < 0.05; ** represents P < 0.01; *** represents P < 0.001; ‘ns’ represents P > 0.05). DPPH: 2, 2-diphenyl-1-picrylhydrazyl; POD: peroxidase; SOD: superoxide dismutase.