Effects Of Glycine Betaine Treatment On Amino Acids Metabolism And AsA-GSH Cycle Metabolism Of Postharvest Peach Fruit

Peach fruit is very popular among consumers because of its attractive aroma,sweet taste and rich nutrition.Low temperature storage is an effective method to prolong the storage time for peach.But peach fruit is a typical cold-sensitive fruit,and if it was putted in an unsuitable low temperature environment for a long time,browning of the flesh,imbalance of sugar and acid ratio,and poor flavor will appear.Based on flavor and metabolic levels,the regulatory mechanism of GB treatment on flavor quality,amino acids metabolism and ascorbic acid-glutathione（As A-GSH）cycle metabolism in peach fruit during cold storage were investigated.We discussed the possible mechanism of glycine betaine（GB）treatment on improving quality and cold tolerance in peach fruit.It could provide sufficient theoretical basis for the application of GB treatment in the preservation of peach fruit.The results were as follows:1.The effects of GB treatment on chilling injury and flavor quality in peach fruit during cold storage were studied.The results indicated that 10 mmol/L GB treatment could significantly alleviate the symptoms of chilling injury,delay electric conductivity and MDA content,maintain higher contents of total soluble solids（TSS）,titratable acidity（TA）,free amino acids and organic acids,and higher levels of sweetness,sourness,umami and richness in peach fruit.Besides,the electronic nose and electronic tongue technology could significantly distinguish the difference in taste and smell of the two groups,and the response value of electronic tongue was correlated with some free amino acids,organic acids,TSS and TA in peach fruit.GB treatment played a positive role in alleviating the symptoms of chilling injury and maintaining better flavor quality in peach fruit during cold storage.2.The effects of GB treatment on metabolite levels in peach fruit were analyzed based on metabonomics.It was found that PCA,PLS-DA and OPLS-DA models could all explain and predict the difference between the GB treatment group and the control group.191 differential metabolites were identified,including amino acids and their derivatives,carbohydrates,lipid molecules,phenylpropane and polyketides,and organic acids.Among them,amino acids and their derivatives accounted for the highest proportion.33 differential metabolic pathways enriched in the KEGG metabolic pathway through those differential metabolites,which were involved amino acids and their derivatives metabolism,biosynthesis of secondary metabolites,tricarboxylic acid（TCA）cycle,ascorbic acid and alginate metabolism and glutathione metabolism.These results provided reference basis for follow-up research.3.The effects of GB treatment on arginine metabolism in peach fruit during cold storage were investigated.It showed that GB treatment could significantly increase the activities of arginase（ARG）,arginine decarboxylase（ADC）,ornithine decarboxylase（ODC）and ornithineδ-aminotransferase peroxidase（OAT）,and induce the genes expression of Pp ARG,Pp ODC,Pp ADC and Pp OAT.This could promote the synthesis of polyamines and proline.At the same time,GB treatment effectively reduced the activities of diamine oxidase（DAO）and polyamine oxidase（PAO）and the gene expression of Pp PAO to inhibit polyamine catabolism.In conclusion,GB treatment effectively induced the accumulation of polyamine and proline by improving arginine metabolism,which could protect the integrity of the cell membrane and reduce the chilling injury in peach fruit.4.The effects of GB treatment onγ-aminobutyric acid（GABA）metabolism in cold storage peach fruit were studied.GB treatment kept higher levels of the activities of glutamate decarboxylase（GAD）and GABA transaminase（GABA-T）,as well as the genes expression of Pp GAD,Pp GABA-T and Pp SSADH,which contributed to the accumulation of GABA and succinic acid.The effect of GB treatment on enhancing the cold tolerance of peach fruit was carried out by regulating GABA metabolism to promote GABA synthesis and provide sufficient succinic acid for the TCA cycle.5.The effects of GB treatment on As A-GSH cycle metabolism of peach fruit in cold storage were investigated.The results demonstrated that GB treatment could improve the activities of ascorbate peroxidase（APX）,monodehydroascorbate reductase（MDHAR）dehydroascorbate reductase（DHAR）and glutathione reductase（GR）,and induce the genes expression of Pp APX,Pp GR,Pp MDHAR and Pp DHAR,which resulted in higher contents of ascorbic acid（As A）and glutathione（GSH）and the ratio of As A/DHA and GSH/GSSG in GB-treated peach fruit.At the same time,GB treatment effectively reduced H₂O₂content.Through regulating As A-GSH cycle metabolism,exogenous GB played a positive role in improving the ability of anti-oxidation and reducing the oxidative damage caused by low temperature.