Biochemical approaches to prevent pericarp browning in Lychee fruit (Litchi chinensis) during storage: A review

Lychee fruit (Litchi chinensis) is widely known for its bright red pericarp and delicious flesh. However, during post-harvest storage, the commercial value of this fruit decreases due to pericarp browning. This browning phenomenon is mainly caused by the enzymatic browning process, which involves the activity of enzymes such as polyphenol oxidase and peroxidase. These enzymes catalyze the oxidation of phenolic compounds to brown pigments, which causes discoloration of the pericarp. In addition, the degradation of anthocyanins, the pigments that give the pericarp its red color, also contributes to the browning. These changes are often associated with cell membrane damage, which allows interactions between enzymes and phenolic substrates. Several post-harvest management measures that can be implemented to delay lychee pericarp browning include storing the fruit at an optimum low temperature (3-5°C) with a relative humidity (RH) above 90-95%. Controlled atmosphere storage, typically using low oxygen concentrations and high carbon dioxide levels, is also quite effective. In addition to optimizing the storage temperature of lychees, several postharvest treatments have been shown to delay pericarp browning. These include the application of natural bioactive compounds, ethylene inhibitors, hormonal and signaling regulators, structural integrity enhancers, edible coatings, and organic acid or antioxidant dips.