Altered energy status in pericarp browning of litchi fruit during storage.

Browning is a major postharvest problem in litchi fruit which results in reduced shelf life and commercial value. Fruit browning could be related to deficient energy, which could result in a gradual loss of compartmentalization of enzymes and their substrates and then initiates enzymecatalyzed browning reaction. Experiments were conducted to further examine the energy status in relation to pericarp browning of litchi fruit during storage. Litchi fruit were treated with exogenous adenosine triphosphate (ATP) or water (control) and then stored for up to 5 days at 25°C. Membrane permeability, production of reactive oxygen species, levels of quinine pool and contents of ATP, adenosine diphosphate (ADP) and adenosine monophosphate (AMP) in pericarp tissues of litchi fruit were measured after 0, 1, 3 and 5 days of storage. Treatment with exogenous ATP inhibited significantly pericarp browning index and the accumulation of ROS. Higher ATP level and energy charge (EC) in the ATP-treated fruit than control fruit were observed. Furthermore, the contents of ubiquinol contents and rates of ubiquinone/total ubiquinone in the control fruit maintained a significantly higher level than those in the ATP-treated fruit during storage. It was suggested that reduced energy production could enhance ROS production, damage membrane integrity and then cause loss of compartmentation between enzymes and substrates leading to enzymatic browning reaction in litchi fruit during storage.