Study On The Effect Of Five Kinds Of Exogenous Substances On The Control Of Chilling Injury Of Postharvest Bananas

Banana is a typical respiratory climacteric fruit.It is easy to rot and soften at room temperature,and is not resistant to storage and transportation.Low temperature storage can delay the ripening and aging process of the fruit and prolong the shelf life.However,banana is a cold sensitive fruit.When the storage temperature is lower than 13℃,the fruit is prone to chilling injury,which seriously affects the quality and shelf life of banana.In this study,clean water was used as control（CK）,bananas（Musa AAA cv.Williams）were treated with calcium chloride（Ca Cl₂）,abscisic acid（ABA）,oxalic acid（OA）,chitosan（CTS）and methyl jasmonate（Me JA）.The banana fruit were refrigerated at 8℃for 10days,and then transferred to normal temperature（25℃）for 10 days.By measuring the physiological and biochemical indexes during cold storage and analyzing the changes of fruit quality after ripening at room temperature,the effects of these five kinds of exogenous substances on chilling injury and storage quality of postharvest banana fruit were compared.The results provide theoretical basis and technical reference for further study on the physiological mechanism of postharvest banana fruit during low temperature storage.The main results are as follows:1.The main chilling injury symptom of’Williams’banana fruit was peel browning.The browning of banana peel of CK treatment was more obviously.Ca Cl₂,ABA,OA,CTS and Me JA treatment could delay peel browning,and effectively reduce chilling injury index of banana fruit.Then the bananas were refrigerated until the 10th day,the chilling injury index of fruit treated with these five kinds of exogenous substances was 20.90%,35.82%,13.43%,26.87%and23.88%lower than that of CK treatment,respectively.Five kinds of exogenous substances could also effectively delay the increase of PPO activity.The results showed that five kinds of exogenous substances could alleviate chilling injury symptoms of fruit by inhibiting browning,which caused by the increase of PPO activity.ABA treatment was the best.2.Five kinds of exogenous substances could inhibit the increase of cell permeability and MDA content.The content of free proline in banana fruit treated with five kinds of exogenous substances was significantly higher than that of CK treatment,which could significantly promote the accumulation of free proline in banana fruit（p<0.05）.ABA treatment had the best effect on inhibiting the increase of cell permeability and MDA content,and promoting the accumulation of free proline.In addition,the decrease of PAL activity in banana fruit was also significantly delayed by the treatment of five exogenous substances（p<0.05）.The results showed that the treatment of five kinds of exogenous substances could reduce the damage of cell membrane,which caused by the increase of cell permeability and MDA content.Five kinds of exogenous substances could promote the accumulation of free proline content in banana fruit,delay the decrease of PAL activity and enhance the resistance of banana fruit.3.Five kinds of exogenous substances could inhibit the increase of H₂O₂content and delay the formation of superoxide anion.The H₂O₂ content of banana fruit treated with five kinds of exogenous substances was significantly lower than that of CK treatment（p<0.05）.The superoxide anion production rate of CK treatment was higher than that of five exogenous substances treatment during 4～6 days,reaching a significant difference（p<0.05）.The activities of CAT,SOD,POD,GR and other antioxidant enzymes in banana fruit were increased.The total antioxidant activity of banana fruit was improved,the ability of scavenging H₂O₂and superoxide anion was enhanced,the content of H₂O₂ and the rate of superoxide anion production were maintained at a low level.And the damage of reactive oxygen species on cell membrane was reduced.4.The results showed that the treatment of five kinds of exogenous substances could not only effectively alleviate the chilling injury of banana fruit,but also maintain good storage quality.After ripening at room temperature,five kinds of exogenous substances could reduce the weight loss,inhibit the rise of soluble solid content,and delay the decrease of soluble protein,titratable acid and vitamin C content.5.The correlation between chilling injury index and each index of banana fruit was further analyzed by visual correlation matrix.The results showed that the chilling injury index of banana fruit in each treatment group was positively correlated with cell permeability,MDA content,free proline content,PPO activity,weight loss rate and soluble solid content.The chilling injury index of each treatment group was negatively correlated with APX activity,hardness,soluble protein content and vitamin C content.The chilling injury index had a high correlation with cell osmotic adjustment substances,enzyme activities and nutrients.Chilling injury seriously affected the storage quality of banana fruit.