Effect And Mechanism Of Postharvest Treatments On Senescence Of Blueberry Fruits

Blueberries (Vaccinium spp.) have become increasingly popular because of their flavor and are consumed as fresh fruit. However, fresh blueberries are highly perishable after harvest, and thus, strategies to maintain or enhance their antioxidant content and increase their storage life are needed. Due to increased health awareness in recent years, there has been interest in enhancing the antioxidant content of blueberries. Antioxidant activity has become an important index to evaluate the quality of postharvest blueberry fruits. Therefore, seeking a green treatment which can both improve the content of anthocyanin in postharvest blueberry fruits and at the same time maintain fruit qualities has been becoming a new hotspot for researches on blueberry preservation. In this study, we selected’Elliott’,’Darrow’and ’Northland’blueberries as materials, the effect of MeJA, salicylic acid and ethanol treatments on quality, senescence and antioxidant system in blueberry fruits were investigated. The main research results are as follows:(1) Treatment with 50 μmol/L MeJA significantly inhibited the increase of decay incidence, weight loss and malondialdehyde (MDA) content, MeJA treatment improved the H2O2 scavenging ability and antioxidant activity by enhancing APX, CAT activities and GSH, total phenolic contents. In addition, fruits treated with 50 μmol/L MeJA exhibited significantly higher ascorbic acid, total phenolic and anthocyanins contents. These results suggested that MeJA treatment might be a powerful strategy to improve the nutritional value and antioxidant activity of blueberry fruits.(2) Salicylic acid treatment significantly inhibited the increase of decay incidence, weight loss and malondialdehyde (MDA) content, maintained TAand TSS values. In addition, fruits treated with salicylic acid exhibited significantly higher ascorbic acid, total phenolic and anthocyanins contents. These results suggested that salicylic acid treatment might be a powerful strategy to improve the nutritional value and antioxidant activity of blueberry fruits. Treatment with 0.5 mmol/L salicylic acid significantly enhanced the total anthocyanin content and antioxidant activity, while 1.0 mmol/L salicylic acid treatment could effectively delayed the senescence in blueberry. Salicylic acid treatment delayed the senescence in blueberry by enhancing SOD, CAT, APX, and PAL activities, the impacts of ascorbic acid and PPO on senescence were impacted by SOD, CAT, APX, and PAL activities.(3) Treatment with 500 μL/L ethanol significantly reduced the rotting of blueberry fruits and inhibited the decrease of TA and Vc content during cold storage. Meanwhile ethanol treatment significantly enhanced total phenolic, total anthocyanin contents and antioxidant activity in fruits. These results suggested that ethanol treatment might be a powerful strategy to improve the nutritional value and antioxidant activity of blueberry fruits. Ethanol treatment delayed the senescence in blueberry by enhancing PAL activity and total phenolic content, the impacts of ascorbic acid, antioxidant activity and PPO activity on senescence were impacted by PAL activity and total phenolic content.(4) The differences in total phenolic, total anthocyanin, and individual anthocyanin among ’Elliott’,’Darrow’ and ’Northland’ blueberries may be due to cultivar type. Treatment with 50 μmol/L MeJA could inhibit the decay of blueberry fruits with different cultivars and degrees of ripening during cold storage, and help to maintain the TSS values of fruits. Meanwhile, MeJA treatment inhibited the decline of the total phenolic and total anthocyanins contents in medium-ripened ’Elliott’,’Darrow’ and ’Northland’ fruits during cold storage, and induced the syntheses of total phenolic and total anthocyanins in highly-ripened ’Elliott’, ’Darrow’ and ’Northland’fruits during the later stage of cold storage.(5) Expression of VcPAL, VcCHI, VcUFGT, VcDFR and VcMYBPA1 genes had been shown to be correlated with anthocyanin accumulation during cold storage in blueberry. MeJA and ethanol treatments induced the syntheses of anthocyanin by enhancing the expression level of VcPAL, VcCHI, VcUFGT and VcMYBPA1 genes, while salicylic acid treatment induced the syntheses of anthocyanin by enhancing the expression level of VcCHI, VcUFGT and VcMYBPA1 genes. MeJA and salicylic acid treatment significantly inhibited the decrease of fructokinase and glucokinase activities, and thus maintained a higher levels of fructose and glucose contents. These results suggested that sugar might participate in the syntheses of anthocyanin in postharvest fruits induced by MeJA and salicylic acid treatments.