Mechanism Of Calcium And 1-MCP Regulating Post-ripening Softening And Near Freezing Temperature Storage Technology Of Melon

Melon(Cucumis melo L.)is highly appreciated by consumers for its nutritious elements,great taste and natural flavor quality.Xinjiang has the largest planting area and the highest yield of melon in China.However,the melon fruits is prone to post-ripening,senescence,quality deterioration,rot and deterioration,etc.Therefore,the storage period and shelf life of melon fruits are restricted severely.Low-temperature is an effective method for storage and preservation.But low-temperature stress often cause chilling injury to melon fruits,which can often induce the pathogen to infect the fruits and lead the fruits to decay.Therefore,it has long been a key task for the melon industry to explore the technology of controlling the post-ripening senescence,improving storage quality,preventing chilling injury,and expanding the storage and shelf life of melon fruits.This paper tried to explore the practical and effective solutions for the problems in the preservation of melon fruits.Taking the‘Xizhoumi 17'for test materials,the physiological mechanism of calcium and 1-MCP in delaying the postharvest senescence and deterioration of melon fruits were studied.Aiming at the chilling injury of melon fruits during low-temperature storage,the methods to improve the low temperature resistance of melon fruits was explored.And the technology of near freezing temperature(NFT)storage had been introduced also.In this research,the effects of different storage methods on quality and shelf life of melon fruits had been analyzed and compared.As a result,a simple,easy-to-operate and practical melon fruits storage methods including harvesting,pre-storage treatment,storage,and shelf life had been initially formed.It provided a theoretical and practical support for the promotion of the combined technology of calcium,1-MCP and NFT storage.Major research fruits are as below:1.The influence of different concentrations of CaCl₂and 1-MCP on respiratory metabolism and ethylene production of‘Xizhoumi 17'fruits had been studied,and the results showed that 2%CaCl₂and 1?L·L^-11-MCP were more suitable for melon fruits treatment.Both CaCl₂and 1-MCP treatments could reduce the respiratory rate and ethylene production of melon fruits.And it could also delay the respiratory and ethylene production climacteric and put off the degradation of fruit hardness effectively.Meanwhile,the soluble solids,titratable acid and Vc in the fruits were maintained well.In addition,a better effect could be achieved by using CaCl₂and 1-MCP in combination than using them along.2.In the ripening and softening process of melon fruits,the ACC and soluble pectin contents,and the activities of ACS,ACO,PG,PME and?-gal were increased significantly.The Ca²⁺-ATPase activity and CaM content showed the closely related to fruits softening,and it were decreased with the increase of ethylene release.Calcium treatment increased Ca²⁺-ATPase activity and CaM content,and reduced PG,PME and?-gal activity in fruits.The activity of ACS and ACO decreased significantly in 1-MCP treatment fruits.And 1-MCP treatment could delay the decrease of Ca²⁺-ATPase activity and CaM content,and increase the activity.of PG,PME and?-gal.This indicated that calcium treatment could reduce the metabolism of cell wall substances by regulating cell energy metabolism and calcium signal transduction,and the activities of PG,PME and?-gal were inhibited.However,1-MCP acts on the ethylene synthesis pathway and reduces the production of ethylene to delay post-ripening and softening physiology of melon fruits.3.During the ripening and softening of melon fruits,the expression levels of Cm-ACS1,Cm-ACO1,Cm-PG,Cm-PME,and Cm-?-gal were increased significantly,but the expression of Cm-CaM were down regulated.Calcium treatment could induce up-regulation of Cm-CaM expression,while the Cm-ACS1,Cm-ACO1,Cm-PG,Cm-PME,Cm-?-gal expression were suppressed.1-MCP treatment inhibited the expression of Cm-ACS1 and Cm-ACO1significantly,it delayed the down regulation of Cm-CaM expression and decreased the expression of Cm-PG,Cm-PME and Cm-?-gal.This indicates that the expression of Cm-ACS1 and Cm-ACO1 could up-regulate the Cm-PG,Cm-PME and Cm-?-gal expression.Therefore,the post-ripening softening process of fruits were promoted.The high expression of Cm-CaM has an inhibition effect on ethylene metabolism and cell wall metabolism genes expression,thereby the fruit ripening and softening process were delayed.When CaCl₂and1-MCP were used in combination,the mechanisms inhibiting fruits post-ripening were able to integrate and complement each other,thus achieving a better effect in inhibiting the ripening and softening of fruit.4.The mature degree of melon fruit has a great influence on its low temperature tolerance.It was found that low temperature resistance of melon fruits improved with the increasing degree of ripeness in this research.The fruits were easy to be infected with pathogenic microorganisms and cause decay after chilling injury.The different pulp tissues of melon fruits had varying freezing points,-2?for the peel,and-4.5?for the pulp,this indicated that the peel was poorer low temperature resistance than the pulp.Through the drying dehydration of melon fruits peel,the freezing point of the peel could be reduced to-3?-3.5?,and the low temperature tolerance performance of peel was enhanced significantly.Therefore,it was suggested that-1?-2?should be selected as the NFT for melon fruits.Subsequent studies had showen that after the peel was dried,the fruit could endure the low temperature of-1.5?for a long time.5.By comparing the chilling injury and rotting of the melon fruits which had been stored at 3?and NFT(-1.5?),it was found that SOD,POD,CAT and APX activity of fruits was higher in-1.5?,but the O₂^-·generation rate and H₂O₂concentration was lower.Since CaCl₂and 1-MCP treatment could delay or reduce the occurrence chilling injury and disease of fruit.As a result,the fruits of the control and treatment group had been stored at 3?appeared chilling injury spots on the 35th and 42nd days,and the decay rate reached 73%and 58%on the 56th day respectively.However,the fruits still had no chilling injury and decay after stored at NFT for 60 days.6.In this study,the change of fruit quality,post-ripening and softening during the storage period and shelf life at 3?and-1.5?were further analyzed.The results showed that the quality indexes of fruits such as fruit hardness,soluble solids,titratable acid and vitamin C content at-1.5?were all better than those fruits of 3?preservation.During the fruits were stored at 3?,the post-ripening and softening physiology had occurred.Therefore,the inhibition of calcium and 1-MCP on fruit ripening and softening were mainly in the storage period.However,the post-ripening and softening physiological metabolism of the control and treatment group fruits were both at a extremely low level under the NFT.And in the storage of shelf life,the fruits had similar changes in post-ripening and softening physiology with the fruits in room temperature.This indicated that the post-ripening and softening physiology of fruits were inhibited by low temperature in the stage of NFT preservation,and the treatment of CaCl₂and 1-MCP before storage play the role of delaying fruits post-ripening and softening mainly in the shelf life stage.7.After the melon fruit had been stored at 3?,which often soften rapidly in the shelf life.By observing cell sliders of the fruit samples,there were many linear fracture marks could be foumd in the cells of the rapidly softened fruits.However,the fruits softened in NFT and normal temperature preservation had not show this phenomenon.By comparing the hemicellulose,cellulose content,XET and Cx activity in fruits,the results showed that the content of hemicellulose decreased rapidly and the activity of XET increased significantly,but the content of cellulose and the activity of Cx had little correlation with fruit softening.At the same time,it was found that the activity of?-gal increased significantly in the fruits of 3?preservation,which may accelerated the hydrolysis of cell wall hemicellulose.In addition,the content of O₂^-·,H₂O₂,MDA and cell membrane permeability were all higher in the fruits of3?preservation,it could promote the fruits post-ripening and senescence in the shelf-life and led to the fruits rot more faster.