Abstract:

【Objective】 Effects of DNP (2,4-dinitrophenol), the uncouple agent for respiratory, on browning and active oxygen metabolism in pericarp of harvested longan fruits were investigated in this paper. 【Method】 The harvested longan fruits were dipped in 0.1 mmol?L-1 DNP for 0.5 h, while, the control fruits were dipped in distilled water. The fruits were dried prior to packaging and stored at (28?1)℃. During fruit storage, pericarp browning index, contents of adenosine triphosphate (ATP) and malondialdehyde (MDA), production rate, activities of active oxygen scavenging enzymes such as superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), contents of endogenous antioxidant substances such as ascorbic acid (AsA) and glutathione (GSH) were determined.【Result】As compared with the control fruits, there were higher browning index and lower ATP content in pericarp of DNP-treated longan fruits. The longan fruits treated with DNP resulted in increased rate of production and kept higher rate of production during the whole storage, reduced the activity of APX and increased the activities of SOD and CAT, significantly decreased the amounts of AsA and GSH, and increased MDA content.【Conclusion】 From the results it can be concluded that DNP-induced browning of longan pericarp may be due to the decrease of active-oxygen-scavenging capacity and the accumulation of active oxygen caused by DNP treatment, which may destroy cell membrane system. And limited energy availability caused by DNP may lead to weaken repair capacity of the damage of cell membrane system. All these factors may disrupt cellular membrane structure, allowing phenolase (polyphenol oxidase, PPO) to react with phenolic substrates and oxidation phenolics to form brown polymers.

Key words: longan (Dimocarpus longan Lour.), pericarp, browning, active oxygen metabolism, limited energy availability, ATP, DNP