Dicyclohexylcarbodiimide and disodium succinate regulate the browning development in fresh longan pericarp by modulating the antioxidant system and the metabolisms of membrane lipids and phenolics

In this study, the effects of dicyclohexylcarbodiimide (DCC) and disodium succinate (DS) treatments on the pericarp browning (PB) development in postharvest longan were elucidated by measuring PB-related phenotypes and the metabolisms of antioxidants, membrane lipids, and phenolics. Compared to the control, DCC-treated longan displayed the higher levels of PB index, CMP, ROS, PA, DAG, and SFAs, the higher activities of POD, PPO, and MLMEs including PLD, PC-PLC, PI-PLC, lipase, and LOX, and the higher expression levels of DlPPO1 , DlPOD1 , and genes encoding MLMEs. In contrast, the lower levels of chromaticity values, pigments, TP, PC, PI, and USFAs, the lower activities of RSEs including SOD, CAT, and APX, the lower expression levels of genes encoding RSEs, and a lower non-enzymatic antioxidant capacity were also noted in DCC-treated longan. These results imply that the exacerbated PB induced by DCC was associated with the activation of MLMEs by up -regulating the expression of genes encoding MLMEs, which expedited the damage of cell membrane. This membrane damage was also regulated by the accelerated accumulation of ROS triggered by DCC. The increased membrane permeability after the damage prompted an enzymatic oxidation between phenol oxidase and phe-nolics. However, the opposite effect occurred in the DS-treated longan.