Effect Of Gas Synergistic Control On Browning Of Fresh-in-husk Walnut Fruit And Its Physiological Mechanism

Fresh-in-husk walnuts?Juglans regia L?have a unique flavor and taste,and the commercial demand is increasing day by day.However,the fresh walnut preservation technology has already fallen into a bottleneck.In this study,using‘Xifu 1'?Juglans regia L.cv.Xifu 1?as material,fresh in-husk walnut were stored under CA?5%O₂+7.5%CO₂?,which screened out in preliminary research,CA?Controlled atmosphere?in combination with exogenous ethylene compensation?Ethylene,Eth?or ethylene inhibition?1-Methylcyclopropene,1-MCP?,cold storage was set as control.During storage,the activity of reactive oxygen metabolism,redox metabolism,energy,senescence-related and cell structure were assayed.Main conclusions were as follows:?1?CA significantly reduced endogenous ethylene production rate and delayed ethylene production peaks compared to controll.0.5?L/L 1-MCP+CA treatment enhanced the inhibitory effect of endogenous ethylene production by CA and reduced ethylene production rate on the middle and late stages of storage.Exogenous low and high concentration ethylene compensation treatment?500?L/L ethylene,8000?L/L ethylene?weakened the CA effect in different degrees,and 8000?L/L Eth+CA treatment inhibited ethylene production rate within 0?14 days of storage.?2?Compared with CK,CA with the synergization between O₂/CO₂ and low levels endogenous ethylene production rate,maintained SOD,CAT,APX,TP,GABA,ASA,GSH contents and energy level,reduced oxidative oxygen(O₂^·-,H₂O₂),the increase of MDA,PPO activity and relative expression level of JrPPOs;improved the soluble protein content and JrCBF expression of 0?14 days,but reduced osmotic adjustment substance?proline?,delayed the browning and softening process of walnut,and maintained the kernel quality.At the same time,microstructure of walnut green husk indicated that CA effectively maintained the integrity of the husk tissue and the integrity of cell structure,delayed the senescence of chloroplast,mitochondrial and various membranes.?3?0.5?L/L 1-MCP+CA treatment inhibited the endogenous ethylene production rate and increased the activity of SOD,CAT,APX and POD on the former stage of storage,but it did not effectively maintain the kernel quality and significantly weakened the effects of CA on total phenols?TP?,?-Aminobutyric acid?GABA?,ASA and GSH content,accelerated the rate of O₂^·-and H₂O₂ in the husk,increased the browning index,played a negative role in walnuts preservation.?4?500?L/L Eth+CA treatment weakened the control act of endogenous ethylene from CA,and partly recovered the production of ethylene.Although the SOD,CAT,APX activity of husk was partially increased on the early stage of storage,but the efftect from CA on reactive oxygen species,redox substances and browning retard were weakened.8000?L/L Eth+CA treatment also partially weakened the control effect of CA on endogenous ethylene,but significantly inhibited the ethylene level of storage within the former 0?14days;The treatment enhanced the antioxidant enzyme activities and the content of ASA-GSH cycle related substances.?5?Comprehensive analysis shows that the effect of optimal O₂/CO₂ in CA on walnut preservation needs to cooperate with the low level of ethylene,and extra ethylene compensation may cause metabolism disorder.Using correlation analysis,principal component analysis and PLS-DA analysis,it was found that the non-enzymatic antioxidant system?TP,GABA,ASA-GSH system?plays a major positive role in function of the preservation of‘Xifu 1'fresh-in-husk walnut,and O₂^·-plays the major negative role.