Role of peroxidase in anthocyanin degradation in litchi fruit pericarp

Postharvest browning of litchi fruit pericarp is a major problem, resulting in accelerated shelf life and reduced commercial value of the fruit. The browning was generally thought to be a rapid degradation of red pigments caused by polyphenol oxidase (PPO) and peroxidase (POD). This work is conducted to understand the role of POD in anthocyanin degradation in litchi pericarp, which is less understood than PPO. POD activity in the pericarp increased consistently with skin browning index during storage of litchi fruit, but was negatively associated with anthocyanin concentration. Although POD cannot directly oxidize litchi anthocyanin in the presence of H2O2 in vitro, the anthocyanin content decreased rapidly after the addition of guaiacol solution, which indicated that the anthocyanin degradation by POD exhibited a coupled oxidation mechanism. Furthermore, anthocyanidin, produced by hydrolysis of the purified anthocyanin, could act as a substrate of POD. Thus, enzymatic browning of litchi fruit pericarp caused by POD may involve an anthocyanase–anthocyanin–phenolic–H2O2 reaction.