| Low-temperature storage causes the loss of flavor material of peach, and affects seriously the fruit quality and market value. The Ocubo was choosed as the material, which is the main cultivars in Beijing area, and is rich fruit flavor but easier to lose the flavor during the low-temperature storage after harvest. This paper thoroughly and systematicly studied the mechanism of the flavor loss and its suppression of synthesis pathway during the low-temperature storage after harvest, as well as its control. The main contents includes: (1) compared with the normal ripening fruit, the changes of characteristic flavor and the mechanism of the suppression of synthesis pathway of two low-temperature storage was studied, one is 5℃(characteristic temperature of chilling) and the other is 0℃(commonly used temperature of low-temperature storage); (2) the function mechanism of cold hardening and treatment with exogenous ethylene improving the synthesis of fruit flavor compounds during the low-temperature storage was studied; (3) the mechanism of low-temperature suppression of peach fruit flavor was studied from two aspects, one is the expression of related enzyme gene of peach fruit flavor synthesis, and the other is the expression of protein when the fruit flavor loss seriously for different storage methods.The results indicate that: (1) for the commercial ripe peaches, the fruit quality is the best when storaging 3d at ambient temperature, correspondingly, the fruit firmness is decreasing, and the extractable juice is increasing, and the volatile compositions of peach pulp are , esters, 13.02%; aldehydes, 17.11%; alcohols, 3.63%; and others such as acids and ketones, 10.32%; alkanes, 37.95%. The change trend of ADH and AAT activity is same to that of alcohols and esters during the storage. (2) the fruit quality begins to decline when storaging 15d at 5℃, and the fruit flavor losses seriously when storaging 30d at 5℃, and the volatile compositions of peach pulp are, esters, 7.52%; aldehydes, 40.32%; alcohols, 8.34%; acids and ketones, 19.61%; alkanes, 14.34%. The fruit quality begins to decline when storging 30d at 0℃, and the fruit flavor losses seriously when storaging 60d at 0℃, and the volatile compositions of peach pulp are, esters, 3.47%; aldehydes, 53.22%; alcohols, 16.01%; acids and ketones, 15.46%; alkanes, 8.07%. Compared with the fruit storaging at ambient temperature, the content of aldehydes increases significantly, the content of lactones increases significantly, and the content of acids and alcohols is increasing and the content of alkanes is decreasing for the low-temperature storaging fruit. The LOX enzyme activity is decreasing at first, and then increasing, the ADH enzyme activity is decreasing and the change of AAT enzyme activity is not obvious. (3) The fruit can better complete the ripen process during the storage process of cold hardening and treatment with exogenous ethylene, and the fruit flavor can better maintained also. The peach fruit after cold hardening does not appear the browning symptoms, and only some specific fruits appear spoilage during the later storage period (50d). The spoilage of the fruit back to the ambient temperature is more serious. The firmness and the browning index of the fruit for 0℃plus exogenous ethylene storage method are higher than that of the fruit after cold hardening, but the extractable juice and the spoilage rate are lower. When storaging for 30d with the treatment of cold hardening, the volatile compositions of peach pulp are, esters, 7.52%; aldehydes, 52.75%; alcohols, 7.26%; acids and ketones, 4.77%; alkanes, 19.8%. The volatile compositions of peach pulp for 0℃plus exogenous ethylene storage method are, esters, 6.39%; aldehydes, 49.74%; alcohols, 7.14%; acids and ketones, 5.05%; alkanes, 26.59%. Compared with the fruit after cold hardening, the content of lactones, aldehydes, and alcohols of fruit for 0℃plus exogenous ethylene storage method are lower, while the content of acids and ketones, as well as the content of alkanes are higher, but the difference are all not significant. The proportion of the content of benzaldehyde to grass-type flavor for the fruit of treatment with exogenous ethylene is far higher than that of fruit after cold hardening. For the fruit after cold hardening, in the midterm of storage period, the content of linalool is higher significantly than that ofγ- decanolactone after back to the ambient temperature, but the two flower-type flavor are not obvious different for the fruit with the treatment of 0℃plus exogenous ethylene. For the two storage methods, the LOX enzyme activity increases larger than that of 0℃storage method. The ADH enzyme activity of the fruit after cold hardening is lower than that of the fruit with the treatment of 0℃plus exogenous ethylene, but the AAT enzyme activity has little difference. And the PG enzyme activity of these two storage methods is higher than that of 0℃storage method, and the PG enzyme activity of the fruit with the treatment of cold hardeing is higher than that of the fruit with the treatment of 0℃plus exogenous ethylene; (4) Fluorescent quantitation was used to the LOX and AAT gene of peach pulp for different storage period, 5℃for 30d, 0℃for 60d, the treatmeng of cold hardening and the treatment plus exogenous ethylene for 60d. The results indicate that compared with the fruit of ambient temperature 3d, the gene expression of the fruits for these four storage methods all decreased, and the the gene expression of AAT is not obvious different. The gene expression of the fruit pulp for the treatment of cold hardening and the treatment of plus exogenous ethylene is higher significantly than that of other two storage methods. Meanwhile, the gene expression of LOX of the fruit for the treatment of plus exogenous ethylene is higher significantly than that of the fruit for the treatment of cold hardening.Through the analysis of the results mentioned above, the following conclusions can be made: (1) According to the threshold concentration of flavor, determined the 5 compounds as the main flavor composition, F aldehyde, anti-2-hexene aldehyde, benzaldehyde, linalool,γ- decanolactone. The fruit use the fatty acid metabolism pathway to form carbamate substance during the process of normal post ripening at ambient temperature; (2) The fruit quality begins to decline at 5℃storage 15d and 0℃storage 30d. Low temperature inhibits the transformation from aldehydes to alcohols, and caused the increasing of the content of aldehydes, the decreasing of esters, and at the same time, induces the expression of LOX, accelerates the fruit ageing at the later storage period; (3) The cold hardening of 8℃is favorable to the pectin from insoluble to soluble state, and promots the softening of fruit, mitigates effectively the woolly. Ethylene catalyse the fruit ripening, better retards the fruit chilling exacerbation, and maks the transformation from aldehydes to alcohols in the fatty acids pathway, maintaines the fruit quality to a certain extent. The cold hardening of 8℃induces the precursors of fruit flavor compositions synthesizes the lactone using theβ-oxidation pathway of the fatty acid synthesis pathway, and the synthesis of aldehydes mainly through the shikimic acid, amino acids pathway. And exogenous ethylene makes the synthesis of lactone from linalool toβ-carotene under the function of LOX. The synthesis of aldehydes is mainly through the fatty acids pathway. (4) The protein expression is different when the flavor loss and the flavor rich. According to the function, the 19 differentially expressed proteins divided into 5 categories, namely, the production of ability, the metabolism, the resistance, the transcription and the cell structure.
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