Effects Of Exogenous Melatonin Treatment On Antioxidant Capacity And Metabolism Of Sugar And Anthocyanin Of Strawberry Fruits

Strawberries are brightly colored and delicious,which are rich in nutrients such as vitamins,minerals,anthocyanins,etc.Strawberries are always used in the processing of canned,sweet and preserved fruits.The quality of strawberry is easily destroyed by various factors after harvest,such as mechanical damage,which will rapid accumulation of active oxygen metabolism in fruit,and damage the cell membrane knot through membrane lipid peroxidation structure,ultimately accelerating the senescence and decay of the fruit.During this period,accompanied by the loss of nutrients such as vitamins,sugar and acids,strawberry completely lost commercial value.It is of great significance to seek a safe and effective post-harvest fresh-keeping method and explore the mechanism of strawberry preservation and nutrition preservation by this method.In this paper,color transformation period（70%ripe）and full-mature period（100%ripe）strawberries were used as test samples to explore the effect of 300μmol/L melatonin on its quality and antioxidant capacity during post-harvest storage.In addition,the effects of sucrose metabolism and anthocyanin synthesis metabolism were also discussed,in order to provide theoretical basis for strawberry postharvest preservation technology.The results are as follows:1.The effects of melatonin on the quality and antioxidant capacity of strawberry fruits with different maturity were investigated.It was found that melatonin treatment can reduce the decay rate of Strawberries of different maturity,delay their decrease of hardness,TSS.In addition,the activities of cell wall metabolic enzymes Cels,PG andβ-gal related to strawberry firmness and quality were also significantly decreased,delaying the decrease of firmness,but the effect on the color of the epidermis is not significant.Melatonin can significantly reduce the accumulation of strawberry MDA and H₂O₂ content and the rate of O₂^·-generation,while improving the hydroxyl free radical,ABTS+free radical scavenging rate.Thereby,melatonin can increase the antioxidant capacity of strawberry after harvest,reduce oxidative damage,and the effect of melatonin on 100%ripe strawberries is better than that of 70%ripe strawberries.2.The effect of melatonin on sucrose metabolism of strawberry fruits with different maturity was investigated.It was found that melatonin treatment can increase the accumulation of total sugar content in strawberries and inhibit the increase of reducing sugar content.The treatment also delays the decline of sucrose content and inhibits its conversion to glucose and fructose.Melatonin also effectively inhibits the activity of AI and SSC,enhances the activity of SSS and SPS,and has a better effect on 100%ripened strawberries than 70%ripe strawberries.In addition,melatonin can delay the decrease of titratable acid content,but has no significant effect on the sugar-acid ratio.3.The effect of melatonin on anthocyanin anabolism of strawberry fruits with different maturity was investigated.It was found that melatonin treatment can increase the activity of PAL,C4H and 4CL and the relative expression in the metabolism of phenylpropane,thereby the content of phenols and flavonoids in strawberries and the antioxidant capacity of strawberries were enhanced.The DFR and ANS activities were also improved,but the relative expression did not change significantly.Therefore,the synthetic ability of strawberry anthocyanin was improved.Melatonin can also increase the content of anthocyanin monomers,especially the content of geranium-3-glucoside,and the effect on70%ripe strawberries is more obvious than that of 100%ripe strawberries.