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Research of Physiological and Biochemical Characteristics, Heat Transfer Characteristics and Cell St

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Tutor: ZhangMin
School: Shanghai Ocean University,
Course: Refrigeration and Cryogenic Engineering
Keywords: cucumber,membrane permeability,MDA,thermal conductivity,cellular structure,enzym
CLC: S642.2
Type: Master's thesis
Year:  2013
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Many subtropical fruits and vegetables, including cucumbers belong to thethermophilic plants. Because of this feature£¬it will determine the subtropical fruits andvegetables particularly sensitive to low temperature, so the symptoms of chilling injurywill occur when they are stored under the inappropriate temperature for some periods.This will cause fruits and vegetables physiological metabolic disturbance, nutrient lossand the time of low temperature stress that continues to extend more corruptions willlead to pathogen invasion as well as affecting the qualities of fruits and vegetables.Cucumber is one of the typical subtropical crops, these experiments takecucumbers as the research object. The purpose is to study the cucumber¡¯s organizationusing its physiological and biochemical parameters when they are under lowtemperature stress, such as membrane permeability, enzymatic activity, Vc, solublesolids, freezing point, cell wall structure, thermal conductivity, etc.). As for ourcountry¡¯s subtropical fruits and vegetables storage technology and the improvement ofthe national standards, the study provides reliable data and theoretical basis. The mainresults were as follows:1. Total soluble solids of cucumber, Vc and titratable acid content were mainly studied.The experimental results show that the cucumbers¡¯ soluble solids, Vc, and titratableacid content decreased with the extension of storage time. But containing soluble solidcontent and storage temperature, cucumber varieties has nothing to do with maturity,and the storage time is inversely proportional to it. Soluble solids content is higher whenreach at a low level of chilling injury, but it is not sure whether there is a direct linkbetween them and it needs to be determined later.Both Vc and titratable acid content were influenced by temperature, the lower thetemperature, the faster the decline rate of the content. Under1¡æstorage temperature,cucumbers¡¯ Vc and titratable acid content is falling the fastest, meanwhile at thetemperature8¡æ,10¡æand12¡æ, the declining rate of storage decreases in turn.At the same time, different varieties of cucumbers¡¯ containment are not the same, Vcand titratable acid content of JinYou is the least compared with ShenQing and RuiQing.RuiQing has the most abundant content among others, but under2¡æstoragetemperature, it will reach the lowest level of the content after6d. Since the Cucumbers are at the different degree of maturity under2¡ælowtemperature stress, the declining rate of the content of titratable acid are similar. Vccontent in cucumbers is inversely proportional to the maturity.After rewarming, titratable acid content fell by20.4%on average as well as Vclevels fell by15.4%on average.2. Study of cucumber antioxidant enzymatic activity, the experimental results show thatcucumbers¡¯ activity of POD, SOD and CAT under1¡æstorage temperature arecompletely suppressed, the activity of the enzyme under8¡æstorage temperature isbelow that of10¡æand12¡æ. SOD¡¯s activity is close to the room temperature afterthe treatment under10¡æand12¡æstorage temperature for8d.The total amounts of SOD decreased the superoxide radical that damages theorganization, the related performance in previous quantity of the MDA¡¯s accumulationis reduced. As the extension of stress time, cucumbers caused by low temperaturedecreases in physiological function but the peroxidation increase, so SOD, POD andCAT ¡¯s combination cannot resist adversity, meanwhile MDA¡¯s content also increased.The lower the temperature, the more serious the degree of inhibition of the enzymaticactivity.3. The study of membrane permeability and MDA¡¯s content in cucumbers, the resultsshow that under different storage temperature, the lower the temperature, the higher thecucumber¡¯s MDA content, this is correspond to the membrane permeability.Different varieties of cucumbers under low temperature stress after the accumulation ofMDA¡¯s quantity are not the same, ShenQing is slightly less than JinYou and RuiQing,the rising trend of the MDA content and membrane permeability is consistent with theMDA content.Different maturity of cucumbers under low temperature stress is characterized bythe maturity, the more mature of the cucumber, the less content of MDA and membranepermeability.After rewarming, MDA content was increased by12.2%, membrane permeabilityis also increases by9.8%. After rewarming for1d, the membrane permeability increasedunder12¡æstorage temperature, which is the slowest compared with8¡æand4¡æ.4. From the study of cucumber chilling injury¡¯s index and cellular structure, the resultsshow that the lower the storage temperature, the larger the chilling injury¡¯s index, andthe chilling injury index¡¯s rising trend, the membrane permeability and MDA¡¯s contentof rising trend are all consistent, but for the response to chilling injury, it is later inMDA and membrane permeability index. Through experimental analysis, butsymptoms of chilling injury will be aggravated after rewarming.Through the observation of the cellular microstructure, it is found that the cellwalls under low temperature stress, the intercellular layer thickness will increases andthe secondary wall thickness will decrease. Stored under the storage temperature of2¡æfor10d, the intercellular layer thickness will increase by68.5%then0d, thesecondary wall thickness will decrease by35.3%, respect to45.5%and17%higher thanin the storage at12¡æ. The lower the storage temperature, the more serious.5. Study of cucumbers¡¯ freezing point and the thermal conductivity, the results showed that cucumber is negatively related to the soluble solids content and the freezing point.Cucumbers¡¯ thermal conductivity increased with the prolong of the low temperaturestress, the rising rate is close to the increased rate of membrane permeability, thus infersthat the reason of the increase of the thermal conductivity may be that cucumbers¡¯ cellsunder low temperature stress increased membrane permeability, cell electrolyte leakagewere in great quantities, which resulted in the increase of the density as well as thermalconductivity.
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