The Mechanism Of Arginine Maintaining Postharvest Pomegranate Fruits Quality During Low Temperature Storage

Pomegranate not only has a good taste,delicious and juicy,rich in amino acids and vitamins,but also has a high health value in medicine,which is favored by consumers in domestic and foreign markets.Due to postharvest respiration,transpiration and mechanical damage,pomegranate fruits are prone to husk browning,aril deterioration,softening and rot after harvesting,resulting in shorter storage periods and poorer quality during storage,thus,reducing commodity value.At present,many studies focused on the nutritional and health functions of pomegranate,but few reports on postharvest storage and preservation.Therefore,in the present study,the pomegranate fruits were harvested during the commercial maturity period,’Tunisia’soft seed and ’Yudazi’ pomegranate fruits were soaked with different concentrations of arginine(0.5,1.0,1.5 and 2.0 mM),without any treatment as CK,to study the changes in physiological indexes and nutritional quality of two pomegranate cultivars during the cold storage period,explore the effects of different concentrations of arginine on the fruit quality during cold storage of ’Tunisia’ soft seed and ’Yudazi’pomegranate,and screen the best treatment concentration.Meanwhile,our study aims to analyze the mechanism of arginine improving pomegranate fruit quality during cold storage combined with the expression level of the related genes,which will provide a more effective and safe method and scientific reference for maintaining the best preservation effect of pomegranate fruits.The research results are as follows:1.The ’Tunisia’ soft seed and ’Yudazi’ pomegranate fruits after arginine treatment during cold storage,effectively reduced the husk browning rate,H2O2 accumulation and free radicals,maintained a higher membrane integrity and DPPH free radical scavenging capacity,higher contents of anthocyanin,Vc and SSC,and improved the antioxidant activity(SOD,CAT,PAL and APX).Therefore,arginine treatment effectively improved the pomegranate fruit quality.2.The comparison analysis of four arginine treatment concentrations(0.5,1.0,1.5,2.0 mM)showed that 1.0 mM was the best concentration for the postharvest two pomegranate cultivars.Our results demonstrated that the pomegranate fruit with 1.0 mM arginine treatment exhibited significantly lower chilling injury and husk browning,and higher membrane integrity because of lower electrolyte permeability and malondialdehyde(MDA)accumulation,which was due to the interaction of the lower accumulation of H2O2,and higher enzyme activity of superoxide dismutase(SOD),catalase(CAT)and ascorbate peroxidase(APX).3.The higher PAL/PPO activity ratio in the husks of two pomegranate cultivars treated with arginine improved the low-temperature tolerance,which manifested as lower browning rate.Pomegranate arils promoted the accumulation of total phenols and anthocyanins content through a higher PAL/PPO activity ratio,and then show higher DPPH scavenging capacity.Especially the PAL/PPO activity ratio in fruits treated by 1.0 mM arginine treatment is the highest,which is about 20%higher than the other three arginine concentration treatments and about 60%higher than the control.4.Through the comparative analysis of the multiple indexes between ’Tunisia’soft seed and‘Yudazi’pomegranate fruits during cold storage,after arginine treatment,the fruit quality of ’Yudazi’ was better than that of ’Tunisia’ soft seed pomegranate.The ’Yudazi’ pomegranate fruits was lighter browning degree,lower cold damage of the membrane and better cold resistance than those of ’Tunisia’ soft seed ones.In addition,the antioxidant enzyme activities in ’Yudazi’ pomegranate arils and husks were also significantly higher than those in ’Tunisia’ soft seed ones.Therefore,’Yudazi’ pomegranate is more suitable for storage than ’Tunisia’ soft seed pomegranate.For ’Tunisia’ soft seed pomegranate,the longest cold storage time for maintaining quality after arginine treatment was suggested about 60 d,and 40 d for CK.Whereas,the ’Yudazi’ pomegranate could store for 80 days,still maintaining better fruit quality and commodity quality.5.According to the genes expression of four antioxidant genes(CAT,APX,SOD,PAL),these genes of ’Tunisia’ soft seed and ’Yudazi’ pomegranate were induced by arginine during cold storage.Our results desmonstrated that the four genes involved in preservation and cold resistance,and improved the preservation effect of pomegranate fruits during cold storage.Especially,’Yudazi’ fruits with 1.0 mM arginine treatment,the expression levels of CAT,SOD and PAL genes were higher on 80 days during cold storage than ’Tunisia’ soft seed pomegranate,which suggested that‘Yudazi’had better storage ability through defending against active oxygen damage.The above results could explain the longer storage time of‘Yudazi’pomegranate.Therefore,through the combination of physiological indicators and gene expression levels,indicating that the four enzymes played an important role in arginine improving fruit quality of pomegranates.The present study demonstrated that arginine treatment can not only attenuate the chilling injury of pomegranate,but also can partially maintain the nutritional value of pomegranate fruit by promoting antioxidant system activity.Therefore,arginine treatment is an effective and promising fresh-keeping technology.