Effect of citric acid and chitosan on maintaining red colouration of litchi fruit pericarp

A postharvest treatment based on citric acid and chitosan was tested on two litchi cultivars of different provenance. Its effects on the activities of polyphenol oxidase (PPO), peroxidase (POD) and anthocyanase and on the anthocyanin content of the pericarp were measured as factors responsible for pericarp browning. The red colour of the pericarp was measured during storage of the fruit. The major anthocyanins present in both cultivars were cyanidin-3-rutinoside and cyanidin-3-glucoside. Although the concentration of cyanidin-3-rutinoside was 64% lower in the cultivar Kwai may (Guiwei) than in Wai chee (Huaizhi), this component represented more than 90% of total anthocyanins in both cultivars. The activity of PPO was six times greater in Kwai may than in Wai chee and the activity of POD was 30-times greater. The activity of POD was greater than that of PPO in both cultivars. The two cultivars, which differ in anthocyanin and oxidative enzyme compositions, responded differently to the acid and chitosan treatment, with the result that the red colour of Kwai may was better preserved during storage than that of Wai chee. This technique could be a future replacement for current sulphur treatments used to treat litchis transported by sea.