Abstract: The effects of oleocellosis induced by orange oil on the membrane lipid metabolism of Navel orange at low ripening stage (nearly ripe) were studied based on collapse index, discoloration index and cell membrane-related substances. Results showed that oil treatment could induce oleocellosis in Navel orange and the severity of oleocellosis increased as time prolonged. Orange oil exerted phototoxic effects on the fruit peel; the cell membrane system was involved in the response of the fruit to oleocellosis. Oil treatment increased phospholipase D (PLD) activity, decreased phosphatidylcholine (PC) and phosphatidylinositol (PI) and enhanced phosphatidic acid (PA) contents, indicating that the severity of cell membrane degradation increased as oleocellosis developed. Lipoxygenase (LOX) activity was also enhanced by oil treatment during the early storage period, thereby leading to the decrease of unsaturated/saturated fatty acid ratio and the accumulation of reactive oxygen species (ROS). Malondialdehyde (MDA) and electrolyte leakage were increased due to the increased contents of hydrogen peroxide (H2O2) and superoxide anion (O2 ?·) during the whole storage. Cell membrane damage contributed to the occurrence of oleocellosis and led to the increase of oleocellosis severity during storage. This study could provide a theoretical reference for exploring the mechanisms and control strategies of oleocellosis.

Key words: Navel orange, oleocellosis, orange oil treatment, membrane lipid metabolism