Effects Of Heat Shock Treatments On Low Temperature Adversity Chilling Injury Of Cucurbita Pepo And Preliminary Analysis Of Tissue Heat Transfer

Cucurbita pepo L were used as the object of this research.The effects of different low temperature storage conditions and low temperature storage after heat shock treatment of Cucurbita pepo on the storage quality and physiological and biochemical characteristics were studied.The heat transfer mechanism of hot water treatment and hot air treatment was analyzed.And cold resistance mechanism of heat shock treatment of Cucurbita pepo and the relationship between heat shock treatment and biological heat transfer was discussed.For provide the theoretical basis and experimental data to the research on the storage and preservation of cold sensitive fruits such as zucchini.The main contents and results of this paper are summarized as follows:1.Study on storage quality and physiological and biochemical characteristics of zucchini fruit under low temperature stress Under low temperature stress?2?,4?,6??,zucchini fruit chilling injury related to storage at low temperature,the lower the temperature,the earlier the chilling injury occourred.Chilling injury of zucchini under the storage of 4? and 6? occourred in the first 6 d,the storage of 2? occourred in the first 3d.And the degree of chilling injury getting further with the storage time.Chilling injury did not happen during the storage of 12?.The activity of antioxidant enzymes?CAT,POD,SOD?was inhibited,the content of MDA and the electrolyte leakage rate were increased,and the content of soluble solids and the content of soluble solids were decreased.In general,inappropriate low temperature adversity reduced the storage quality and destroyed the normal physiological and biochemical of zucchini,and samples stored on 2? situation is the most serious one.2.Study on storage quality and physiological and biochemical characteristics ofhot-water treated zucchini fruit During the 4? low temperature storage process,firmness of fruits was improved,the35 ? treatment had a certain effect on weaken the decrease of chlorophyll content,the soluble sugar content in the pre-storage period was increased?from the 0th to the 6 th?,the decrease of soluble sugar content was inhibited in the later period of storage?from the 12 th to the 15 th?,the content of soluble protein was increased to a certain extent,the reducing of TSS content was alleviated,respiratory strength was reduced,and good storage quality was maintained of zucchini fruits which were pre-treated fully in hot water of 45?and 55? for 5min and 10 min.The content of H₂O₂ in heat-treated fruitswas higher than the control within the first 3d,and the treatment reduced the H₂O₂ accumulation at middle and later period of storage?from the 6 th to the 15 th??P <0.05?.And the increasing content of O₂^-was reduced?P<0.05?,the activities of CAT and SOD were increased in the early period of storage?from the 0th to the 6 th?,and the activities were decreased in the later stage?from the 6 th to the 15 th?,especially the POD activity was significantly increased in the late period of storage?from the 6 th to the 15 th?,the content of MDA and the relative conductance was decreased in heat-treated fruits,and 35 ? hot water-treated for 10 min was better.The results indicated that hot water treatment induced the cold resistance of zucchini under low temperature stress,stimulated the activity of antioxidant enzymes,increased the scavenging ability of free radicals,delayed the process of cell membrane lipid peroxidation,and thus effectively alleviate the chilling injury.3.Study on Storage Quality and Physiological and Biochemical Characteristics of Hot-air Treated Zucchini Fruit After hot air treatment,zucchini fruits were stored at 4?.The respiration intensity of the fruit was reduced,breathing jump time was delayed,the peak of respiration showed up at the 6th day by 35?hot-air treated for 40 min,respiration peak appeared on the 9th day by 45? hot-air treated for 20 min.And the chilling injury appeared on the 9th day,and the chilling injury of the hot air was also reduced.Simultaneously,the softening degree of the fruit was weakened,the soluble solid content,the soluble sugar content and the soluble protein not only as the nutritional quality but also as the cold resistance indexweremaintained better than the control,thus the storagequality of fruit was improvedand the storage time of fruits was extended.The H₂O₂ content of hot air treatment zucchini was increased by stimulated after shorthot air,then decreased and decreased below the control.TheO₂^-content was increased,?CAT,SOD,POD?activities of the antioxidant system was stimulated and increased,so that the scavenging ability of free radicals was increased,the degree of oxidation of fruit tissue was reduced,thereby the protection of the cell membrane systemenhanced.MDA content was relatively small,the degree of membrane lipid peroxidation waslow,the electrolyte permeability decreased,then improving the cold resistance of the zucchini fruit.Thereby the ability of zucchini resisting low temperature adversity was enhanced,and the effect of hot air treatment at 35 ? is better.4.Biological heat transfer preliminary analysis of zucchini fruit in the progress of heat shock treatmentThe temperature change during the heat shock treatment process of different maturity zucchini fruits was determined,and it was found that the lower the maturity of zucchini fruit the worse the ability of heat transfer.Compared withinternal temperature changes of different location during the progress of hot water and hot air treatment on zucchini fruit,the result showed that the closerdistance from the center of the fruit,the longer the time needed for heat transfer,the slower the heat transfer rate,and heat transfer speed of hot water treatment was faster.For the same heat transfer medium?water or air?,the higher the heat treatment temperature,the greater the heat transfer power of the zucchini,the faster the temperature rised,the earlier the temperature reachedto the treatment temperature.The dimensionless excess temperature of hot water and hot air treatment showed a downward trendwith the treatment time,the dimensionless excess temperature of hot water treatmentreduced greaterthan the hot air treatment,and the excess temperature reduced to zero usedless time.The closer the excess temperature distance to the center of the fruit,the longer oh the time for the excess temperature reducing to zero.The change of the heat transfer rate of the central temperature of zucchini fruit in hot water and hot air treatment was tested.Founded that the rate of heat transfer process showed a rapid increase in the first few minutes before reaching to the highest rate,and declined continuously after reaching to the highest rate,rate of hot water treatment is almost twice of the hot air.