Study On Postharvest Physiological Disorder Of Soft Nose In "Keitt" Mango

Mango（Mangifera indica L.）is a tropical fruit with rich nutritional value,which is attracted to consumers.However,the large-fruited mango is susceptible to physiological disorder such as soft nose,resulting in the reduction of the commodity rate.In this paper,the differences in fruit quality,mineral elements,reactive oxygen species（ROS）and antioxidant metabolism,and fatty acid metabolism of late ripening large-fruited mangoes‘Keitt’were investigated at different mature periods and different soft nose grades under postharvest storage at room temperature（25±1°C）,with the aim of analyzing the patterns and mechanisms of postharvest soft nose development in mango.The main results were as follows:（1）During postharvest ripening,the disorder index of mango soft nose increased during the postharvest mature periods and the occurrence of soft nose was positively correlated with the fruit maturity.Compared to the good mango,the quality of soft nose fruit decreased,mainly manifestations in L*and b*values,lower titratable acid（TA）,lower fructose and glucose content,and increased soluble solids（SSC）and sucrose content.（2）The interaction among Ca,Mg,P,K and Na elements led to the occurrence of soft nose,mainly manifested between Ca and P.The Correlation analysis and DRIS index of mineral elements indicated an uneven distribution of mineral elements in soft nose affected mango compared to the good fruit,with excess of P,K,Na and Mg,and lack of Ca.（3）The onset of postharvest mango soft nose may be related to ROS accumulation and membrane lipid peroxidation.Compared to the good fruit,postharvest mango soft nose disordered fruit showed increased lipoxygenase（LOX）activity and the gene expression levels of Mi LOX1,Mi LOX2,Mi LOX3;increased superoxide anion（O₂^-）production rate and hydrogen peroxide（H₂O₂）accumulation,while the activities of superoxide dismutase（SOD）,catalase（CAT）,peroxidase（POD）and glutathione reductase（GR）enzyme were increased,the expression of Mi SOD1,Mi CAT1,Mi PODA2,Mi APX3 and Mi GR gene expression were upregulated,and the ascorbic acid-glutathione cycle（As A-GSH cycle）capacity was increased.However,the total antioxidant capacity（T-AOC）decreased,the increase of LOX enzyme activity,and the accumulation of ROS indicated that the rate of ROS production was greater than the rate of clearance,leading to membrane lipid peroxidation along with an increase in the malondialdehyde（MDA）content.（4）The onset of postharvest mango soft nose may be related to changes in fatty acid content and increased metabolic capacity ofα-linolenic acid.Compared to the good fruit,relative increased in saturated and unsaturated fatty acid content in mango soft nose disordered fruit.Among them,the content of very long chain fatty acids（VLCFAs）and linoleic acid decreased and the content ofα-linolenic acid increased significantly.The expression levels of genes related to fatty acid synthesis,including Mi PLDβ2,Mi ACC1,Mi Fab Z,Mi Fat A,Mi Fab2,Mi FAD6 and Mi FAD3,increased and the expression levels of Mi KCSL4 genes decreased,which were consistent with the trend of fatty acid.Inα-linolenic acid metabolism,allene oxide synthase（AOS）and allene oxide cyclase（AOC）activities increased,and the gene expression levels of Mi ACSL7 and Mi ACOX1 increased,which promoted fatty acid oxidation.In summary,we speculated that unbalanced distribution of mineral elements such as Ca and P,ROS accumulation,increased fatty acid content,and enhanced metabolism ofα-linolenic acid in mango fruit might related to the occurrence and development of soft nose.