Studies On The Metabolism Of Organic Acids In Citrus Guanxi-miyou (Citrus Grandis (L.) Osbeck.cv.guanxi Miyou) Fruit After Harvest

The organic acid concentrations and the relative enzymatic changes in Citrus guanxi-miyou fruit were studied and we probed their interrelationships and the mechanism of the organic acid metabolism to clarify the reason and the mechanism of the fruits' acidification after harvest. And the metabolism of free radicals was investigated. The results were as follow.The organic acids in Citrus guanxi-miyou fruits' maturation stage were adequately determined by Ion-exchange chromatography. The performing gradient elution with EG40 eluent generator was used to obtain a flat baseline and better reproducibility. Results showed that the organic acids in fruits included citrate , quinic acid, oxaloacetate, malate, tartartate , oxalate and cis-aconitase.And the citrate acid,which occupied 75 to 86 percent of the total acids ,was the top organic acid in fruits. In fruits' maturation stage,the activities of NAD-IDH/Aconitase were low and descending,so the resolution of the citrate was little.In all,it was because of the decrease of the synthesis of the citrate that the total titratable acidity dropped in fruits' maturation stage.That was related to the decline of the activities of CS and PEPC.The reasons of the decrease of the total titratable acidity in fruits could be concluded into two aspects:Firstly,as the fruits grew up,the water increased constantly ,which caused the effect of "physiological dilution"; Secondly, the changes of enzymatic activities restrained the synthesis of the citrate and the acids continued their oxidative cleavage.The components of the organic acids in the fruits,whether before or afterharvest, were similar while the contents of the organic acids especially the citrate acid,were different.Fruits went sour when stored at room temperature for three weeks.We used the Ion-exchange chromatography to determine the components and the contents of the fruits.Results showed that the increasing tendency of the citrate was unanimous to the total titratable acidity.And the contents of the citrate kept between 75 and 86 percent of the total acids and the others were little.In conclusion,the fruits went sour because the contents of the citrate increased to a great extent. When the fruits went sour,the activities of CS and PEPC rose and NAD-IDH/Aconitase went down.As the citrate synthesized more and decomposed less,the citrate accumulated and the fruits went sour.The contents of the total titratable acidity went down when stored at low temperature. The changing tendency of the citrate was identical with the total titratable acidity.And the contents of the other organic acids were similar to the fruits stored at room temperature.The activities of CS and PEPC were both low while that of the NAD-IDH/Aconitase was high.Then the citrate synthesized less and decomposed more,and the citrate didn1 accumulate much. So the results showed that when stored at low temperature(6°C) the fruits didnt go sour.When the fruits were stored at room temperature,the activities of POD had two active peaks. The activities of SOD rose quickly in the earlier stage then decreased,and increased to a great extent in the later period of storing.When the fruits were stored at low temperature,the activities of POD were higher than stored at room temperature. The activities of POD rose quickly in the earlier stage ,then decreased,and increased in the later period of...