Abstract:After harvested longan (Dimocarpus longan Lour. ‘Fuyan’) fruits were infected by Phomopsis longanae Chi, the changes in lipoxygenase (LOX) activity, fatty acid constituents of membrane lipids and cellular membrane permeability in pericarp were studied. The results showed that the browning index, LOX activity and cellular membrane permeability increased in pericarp of longan fruits infected by P. longanae. The unsaturated fatty acids, such as linoleic acid (C18∶2), linolenic acid (C18∶3) and gondoic (C20∶1), decreased, while the saturated fatty acids, such as palmitic acid (C16∶0) and stearic acid (C18∶0), increased, and the index of unsaturated fatty acids (IUFA) and unsaturation degree of fatty acids decreased. These suggested that longan pericarp browning induced by P. longanae might be due to LOX activity increment and degradation of unsaturated fatty acids of membrane lipids acceleration, which caused the integrity of cellular membrane structure breakage, in turn, the cellular compartmentation function loss, resulting in the contact of polyphenol oxidase (PPO) with phenolic substrates and subsequent oxidation phenolics to form brown polymers.
