H2O2 content was determined by the previous method of Cheng et al. (2007). Fresh peel tissues (2.0 g) from ten fingers withdrawn randomly from each treatment was homogenized with 10 mL of cold acetone, and then centrifuged at 12,000 × g for 30 min at 4 °C. One milliliter of the extract solution was mixed with 0.1 mL of 5% titanium sulphate and 0.2 mL ammonia, and then centrifuged at 12,000 × g for 10 min at 4 °C. The pellets were dissolved into 3 mL of 10% (v/v) sulfuric acid solution, and then centrifuged at 12,000 × g for 10 min. The absorbance of the supernatant was measured at 420 nm. The known concentrations of H2O2 were used to make a standard curve. The H2O2 content was expressed on a fresh weight basis as mmol kg−1.