Effect And Mechanism Of Exogenous Melatonin On Postharvest Quality Of Cucumber And Chilling Tolerance Of Cucumber

Cucumber is crisp and rich in nutrition,with weight-reducing and beautifying,preventing constipation,improving body immunity,anti-aging,longevity and other effects.It's popular for special flavor,but cucumber is a kind of vegetables with short storage time(2-3 days)at ambient temperature.Melatonin as an antioxidant can directly scavenge free radicals,enhance the plant stress resistance.Studies have shown that melatonin can prevent senile dementia,promote sleep and anti-cancer.The objective of this study was to optimize postharvest melatonin handling conditions to determine suitable storage conditions.To make clear the effect and mechanism of exogenous melatonin on postharvest quality of cucumber and chilling tolerance of cucumber,and provide reference for the effect of exogenous melatonin treatment on postharvest fruit.The main results are as follows:(1)Single factor and orthogonal experiments were conducted with the sensory evaluation,weight loss rate,firmness and soluble solids content as evaluation index.Determine the proper storage conditions for cucumber: melatonin concentration is 100?mol/L,the soaking time is 30 min,the storage temperature is 10?.(2)The cucumbers were dipped in 0,50,100 or 500 ?mol/L melatonin solution immediately after harvest.Changes in quality were monitored periodically during storage at 10 ? for 15 days.Results indicated that exogenous melatonin treatment slowed down the decrease of chlorophyll,vitamin C,and the content of titratable acid and soluble protein of postharvest cucumber during storage.The further study showed exogenous melatonin treatment reduced the fruit relative conductivity,MDA content,active oxygen content and maintained higher activity of antioxidant enzymes(SOD,CAT,POD,APX),and also inhibited the respiration intensity,the ethylene production and the growth of bacteria and fungi,reduced the oxidative chilling injury damage to cells and maintained a more complete cell structure.100?mol/L melatonin solution dip showed the highest overall quality,lowest respiration intensity,MDA content,and maximum reduction of oxidative damage on the cells.(3)The cucumbers were dipped in 0,50,100 or 500 ?mol/L melatonin solution immediately after harvest.Changes in quality were monitored periodically during storage at 2 ? for 12 days and at ambient temperature for 2 days.Results indicated that exogenous melatonin treatment improved the sensory evaluation scores of cucumber,inhibited the chilling injury index,weight loss rate,the relative conductivity and MDA content to reduce the cell membrane damage chilling injury,slowed down the decrease of soluble protein,vitamin C..And also inhibited the respiration intensity,the content of ROS and maintained higher proline content.Exogenous melatonin treatment can effectively improve the chilling tolerance of cucumber 100?mol/L melatonin treatment had the best effects.