Effects Of Oxalate Treatment On Mango Fruit During Storage And Its Mechanism Involved

Effects of oxalic acid treatment on ASA-GSH circle and cell wall hydrolase and oxalate treatmant on postharvest quality, physiological response and decay incidence in mango fruit (Mangifera indica L.cv.Hongmang No.6) were investigated in this paper. Mango fruit dipped in 5 mM oxalic acid and 20mM oxalate solutions for 10 min, respectively, and then stored at room temperature (25℃). Changes in ripening process and decay incidence combined with physiological responses such as ASA-GSH, cell wall metabolism, activity of antioxidant enzymes, defense enzymes, production of radical oxygen species (ROS) in mango fruit were measured during storage. The results showed as following:1) The decrease in fruit firmness and rate of peel degreaning were inhibited in mango fruit with oxalic acid treatment. Contents of ascorbic acid (ASA) and glutathione (GSH) increased, and the levels of ROS (superoxide, O2; hydrogen peroxide, H2O2) and lipid peroxidation effectively reduced, and activities of ascorbic peroxidase (APX) and glutathion reductase (GR) increased in treated mango fruit at the later time of storage. Furthermore, activities of polygalacturonas (PG), a-galactosidase (α-Gal) and p-galactosidas (β-Gal) in treated mango fruit also effectively decreased. The effects of oxalic acid could therefore contribute to maintaining the membrane integrity, slowing fruit soft and delaying ripening process in mango fruit.2) As compared to control fruit, the decrease in fruit firmness and rate of peel degreaning were inhibited, while ratio of titratable acidity (TA) to total soluble sugar (TSS) was increased, and weight loss, diease index and decay incidence were decreaed in mango fruit with oxalate treatment. In addition, activities of both antioxidant enzyme (including POD, SOD and APX) and defense enzyme (such as PPO and POD) in the peel of treated fruit increased, whereas MDA production and LOX activity in the peel decressed, and total phenolic and H2O2 enhanced in mango fruit treated with oxalate. It was suggested that these physiological effects of oxalate could contribute to delaying the ripening process and improving the disease resistance in mango fruit during storage at room temperature.