Synergistic Regulation Of Sugar Conversion In Postharvest Nectarine By Chitosan And Sodium Hydrosulfide

Nectarine is popular among consumers because of its rich nutrition and unique flavor.However,the nectarine fruit has thin skin and high tissue moisture content.It is easy to soften and rot after harvest and has a short storage time.Sugar content in fruits is one of the most important factors affecting fruit quality and flavor.Meanwhile,sugar is also an important source of energy for fruits and is closely related to the development,maturation and senescence of fruits.Therefore,regulating fruit sugar conversion is of great significance for prolonging fruit storage time and maintaining nectarine fruits quality.Chitosan(CS)and sodium hydrosulfide(NaHS)are widely used in postharvest storage of fruits,but the combination of the two for fruit preservation and the regulation of postharvest fruit sugar conversion have not been reported.In this paper,"Linqu nectarine"was used as experimental material,and 5 g·L^-1 chitosan and different concentrations of NaHS(0,0.3,0.4,0.5 mmol·L^-1)were used to co-process postharvest nectarine fruits.Based on the detection of nectarine fruits quality indexes and hydrogen sulfide biosynthesis during storage,the effects of synergistic treatment of chitosan and sodium hydrosulfide on the storage quality of nectarine fruits were analyzed.From the perspective of sucrose metabolism,hexose metabolism and cell wall metabolism,combined with respiratory metabolism and energy metabolism,the synergistic regulatory of chitosan and sodium hydrosulfide on sugar conversion of postharvest nectarine fruits was discussed.(1)Compared with other concentrations,the synergistic treatment of chitosan and 0.4mmol·L^-1 NaHS delayed the decrease in firmness of nectarine fruits,reduced the respiration rate of the fruit during storage,and increased the content of soluble solids(SSC)in nectarine.The activity of related enzymes and the content of metabolites in the catalytic process of L-cysteine are increased,and the endogenous H₂S content of the fruit is increased,thereby maintaining the storage quality of postharvest nectarines.(2)The synergistic treatment of chitosan and 0.4 mmol·L^-1 NaHS promoted the conversion of fructose and glucose to sucrose by increasing the synthesis activity of sucrose phosphate synthase(SPS)and sucrose synthase(SS)in nectarine fruits,and by inhibiting the decomposition activity of acid invertase(AI),alkaline invertase(NI)and sucrose synthase(SS)to delay the decomposition of sucrose.At the same time,the increase of hexokinase and fructokinase activity accelerated the decomposition rate of glucose and fructose,so it effectively maintained the high sucrose content and low fructose glucose content in the nectarine fruit,maintained the higher quality of the nectarine fruit,and then delayed the decrease of fruit firmness.(3)The synergistic treatment of chitosan and 0.4 mmol·L^-1NaHS significantly inhibited the activities of polygalacturonase(PG),pectin methylesterase(PME),xyloglucan endotransglycosylase(XET),?-galactosidase(?-Gal)and cellulase(Cx)and other fruit cell wall degradation enzymes,thus reduced the degradation of cell wall polysaccharides and maintained the integrity of nectarine fruits during storage cell structure.Therefore,it could delay the senescence of nectarine fruits and maintain the quality of nectarine fruits.(4)The synergistic treatment of chitosan and 0.4 mmol·L^-1 NaHS ensured the integrity of mitochondrial structure and cell membrane by increasing the activities of succinate dehydrogenase(SDH),cytochrome oxidase(CCO),H⁺-ATPase,Ca²⁺-ATPase and other energy synthesis enzymes and maintaining high ATP,ADP content and energy charge level in nectarine fruit.Therefore,it delayed the senescence of nectarine fruits.The results showed that the synergistic treatment of chitosan and 0.4 mmol·L^-1 had the best preservation effect on postharvest nectarine fruits,and the storage quality of postharvest nectarine fruits could be maintained by regulating the sugar conversion of fruits.