Effect Of Electron Beam Irradiation On Fresh Walnuts

In order to prolong the post-harvest storage period of fresh walnuts and reduce the quality deterioration caused by storage,different doses of electron beams(1,3,5 k Gy)were used to irradiate fresh walnuts.Analyze the mechanism of changes on postharvest preservation of walnuts during storage after irradiated by high-energy electron beams from the perspective of lipoxygenase.The effects of different preservation methods(fresh food at4°C,frozen storage at-18°C,and dried by hot air)on the quality of walnuts during storage were analyzed and compared.The results showed that the activity of lipoxygenase decreased significantly with the increase of irradiation dose.The high-energy electron beam changed the secondary and tertiary structure of lipoxygenase,and the protein structure changed to disorder.The sulfhydryl content of lipoxygenase treated by dose of 5k Gy decreased to 33.33% of the control group,the carbonyl content increased significantly,and the decrease of the enzyme decreased most significantly.The number of molds in fresh walnuts treated with three doses was significantly reduced in different subsequent storage processes,and the number of molds in walnut stored in-18℃ and dried with hot air did not exceed the national standard within 6 months.The lipoxygenase activity and the oxidation of the fresh walnuts irradiated with 1k Gy which were stored at 4℃ for 91 days were decreased while the content of UFA increased and the sensory quality changed not significantly.The total phenolic content of walnuts was higher than control group which was beneficial to the improvement of the overall antioxidant activity of fresh walnuts during postharvest storage and to reduce the loss of nutrients in walnuts.In conclusion,1k Gy dose irradiation is beneficial to the postharvest storage of fresh walnuts stored at 4℃.The irradiated fresh walnuts were dried by hot air and frozen at-18℃ separately.Results shows that drying promoted the expression of peroxidase activity in walnut which had a certain inhibitory effect on the oxidation of oil in walnut.And it could maintain the quality of oil to a greater extent.The acid value content range from 0.1 to 0.35 mg/g.The acid value of the frozen walnut increased slightly while it was relatively stable during storage.The increasing trend of malondialdehyde content was not significant.The storage period of fresh fruit was relatively short and the enzyme activity was the highest among three groups.The lipoxygenase activity measured immediately after irradiation was separately 16.02 and 16.36 times as much as other two groups.and the magnitude of the change is also the largest.After comparison,treating fresh walnut with the dose of 1k Gy of electron beam irradiation as the pretreatment process before drying and freezing can inhibit the activity of lipoxygenase and delay the oxidative rancidity of oil as well as reduce browning.It can also maintain the sensory quality which is conducive to improving the quality of walnuts.Therefore,1k Gy is the optimal dose of high-energy electron beam treatment for postharvest processing and preservation of fresh walnuts.