PPO activity was determined as described in Fu et al., 2007 and Du et al., 2009 . The samples were homogenized with sodium phosphate buffer (0.2 mol/L, pH 7.0, consisted of 2% polyvinylpolypyrrolidone, stored at 4 °C) at the ratio of 2.0 mL:1.0 g (buffer lotus root) in an external ice bath for 3 min.