Abstract:The effects of 2,4-dinitrophenol (DNP, a uncouple agent for respiratory) on lipoxygenase (LOX) activity, fatty acid constituents in membrane lipids and cellular membrane permeability in harvested longan (Dimocarpus longan Lour. ‘Fuyan’) pericarp were investigated and the relationship to pericarp browning was analysed. The results showed that the cellular membrane permeability, LOX activity and browning index increased treated with DNP, the saturated fatty acids, such as palmitic acid (C16:0) and stearic acid (C18:0) increased, and the unsaturated fatty acids, such as linoleic acid (C18:2), linolenic acid (C18:3) and gondoic acid (C20:1), and index of unsaturated fatty acids (IUFA) and unsaturation degree of fatty acids decreased. It suggested that the pericarp browning of longan induced by DNP might be due to increasing LOX activity, enhancing degradation of membrane unsaturated fatty acid and reducing integrity of cellular membrane, which it lead to finally the contact of phenolase with phenolic substrates to produce browning polymers.