Study On The Effect Of Modified Atmosphere Package (MAP) On Preservation And Postharvest Physiology Of Green Walnut Fruit

Walnut （Juglans regia L.） for fresh fruit is of high nutrional value and better flavor thandry ones, but it is problemic to extend the shelf life of the fresh walnut in practice. Based onthe primary recognization which discoved in previous research that controlled atmospherepackaging （MAP） is effective for the preservation of green walnut fruit, this studyinvestigated further the effect of different plastic film on the preservation of the fruit. Fruit ofChinese walnut cv.Xifu No.2. were stored with three different packaging of PE30（30μm）,thk-PE（45μm）, PE50（50μm）, using mulch plastic film（6μm）package as control. CompoundEffect of either different gradient of ClO₂or1-MCP for the packaging were explored. Thegreen walnut fruit were stored under0¹â„ƒ, RH70%to80%. Gas concentrations in each bagwere measured during the storage; respiration rate, ethylene production rate, water content ofpeel and kernel, soluble solid content, antioxidants content and antioxidant activity, defenseenzyme activity of green husk, and the decay indexe of fruit preservation were statisticed.Kernel traits before and after storage were determined. All the work aim to get more accurateparameters for modified atmosphere （MA） preservation of green walnut fruit and providetechnological basis for application. The resuits as follows:（1） The three packaging had more obvious effect of air modification than control, thethicker the package, the lower volume fraction of O₂; the higher the volume fraction of CO₂,the more obvious the effect was. MA packaging all delayed the first respiratory leap,restrained the second respiratory leap as well as ethylene production climacteric; the level ofthe SSC content were all higher than control, the water content and the firmness of walnutpeel all decreased lower than control. （2） The three packaging had more obvious effect on the antioxidants metabolism of thewalnut green husk than control; Fruit from the three MA packaging all showed peak of totalphenolic content and flavonoid content on18d and36d-storage, and so did PAL activity. Thethree packaging could significantly reduce PPO activity and maintain higher POD activity inthe late stage of storage, the effect of PE50was most significant; in addition, the totalantioxidant capacity （TAA） of the three MA packaging under each observation point were allsignificantly higher than control（P<0.05）, among the three, the total antioxidant capacity ofthk-PE packaging was the highest; the PAL activity showed the correlation with the change ofthe respiratory leap, total polyphenols and flavonoids content.（3） The three kind of thickness packaging all inhibited the decrease of the water contentof the kernel and the increased acid value and peroxide value of the kernel, alleviated thedecrease of the free fatty acid content and reduced the free fatty acid loss after the storage,PE50packaging showed the most significant effect. After60d-storage, the decay index ofPE50、thk-PE、PE30packaging and the control were8.40%,17.7%,29.4%and45.8%; thepreservation rate of kernel allexceeded97%, especially PE50, it had reached100%.（4） Combined treatment with different gradient of ClO₂resulted in a higher volumefraction of O₂and a lower volume fraction of CO₂than the single MA packaging, weakeningthe effect of air modification of MAP and reduced the respiration leap. The ethylene releaseof50mg/L ClO₂and80mg/L ClO₂treatment rebounded, but the SSC content and the firmnesswere not apparently influemced.（5） The respiration and ethylene release of the thk-PE packaging combine the1-MCPcompound treatment was further reduce compare with the MA packaging, but the ethylenerelease peak was recoveried with recombine of80mg/LClO₂, with recombine the p-hydroxybenzoic acid butyl ester it disappear. All chemical compound treatment had not significanteffect on the SSC content and the firmness. According to statistical data, the lowest decayindex was observed on50mg/LClO₂treatment, ie19.4%, there were no significant differencewith the control （thk-PE）, but the chemical treatment was significant higher than the singlePE50packaging（P<0.05）; the decay index of green walnut fruit with the MA packagingcombine the1-MCP compound treatment were all exceeded25%.（6）The different gradient of ClO₂treatment and the1-MCP with ClO₂, p-hydroxybenzoic acid butyl ester compound treatment all could not inhibit PPO activity and the totalantioxidant capacity had not appearance change compare with the single thk-PE packaging.But it has some effect on relieve the reduce of the content of total polyphenols and flavonoidswith the combine ClO₂treatment, even compound the1-MCP or not.（7） Among the three gradient of ClO₂treatment, the strongest ability of water retention of the kernel of green walnut fruit was50mg/L ClO2treatment, but had not showedsuperiority compare with PE50packaging even though had better ability of water retentionthan thk-PE packaging. The kernel acid value and peroxide value of the three gradient of ClO2treatment were all significantly higher than that of thk-PE packing （P<0.05）, and there wasneither effectively inhibit the loss of the amount of free fatty acid nor maintain the amount ofunsaturated fatty acids, for this reason, the three gradient of ClO2treatment were notconducive on maintain the quality of the kernel traits.