| In this paper, we used the fruit flesh and pericarp of Citrus sinensis Osbeck cv. 'Anliu' and its mutant Red Anliu sweet orange as the experiment materials. The content of the major sugars and organic acids in the fruits were analyzed by gas chromatography (GC). We have surveyed the kinds of main sugars and organic acids, the content and the ratio of each component at five development stages of the fruit. To find the differences and correlations between the two materials, we have compared the contents of every component in the process of fruit development and in different parts of the fruit. The major results are as follows:1. A capillary gas chromatography (CGC) method for the simultaneous determination of organic acids and sugars extracted from the fruit flesh and pericarp was established. We found the major components of sugar are sucrose, fructose and glucose, and citric acid, malic acid and quinic acid are the major acids. The use of two internal standards allowed an accurate quantitative analysis of the compounds detected in the unknown samples. Sugars and organic acids have to be converted to their trimethylsilyl (TMS)/TMS-oxime derivatives prior to separation and detection by CGC. The results of the CGC condition have a good coefficient in the range of standard curve.2. The detection of the content of sugars and organic acids in Anliu sweet orange and Red Anliu sweet orange suggested that the content of citric acid and sucrose is much different, but fructose and glucose are different in autumn.Citric acid is the major acid in juice sac. In Anliu sweet orange, the content of citric acid accounts for from 63.1 % to 82.3 %, it dominates the change of total acid in juice sac. On contrast, the content of citric acid in Red Anliu sweet orange is much lower. Although the content of citric acid in Anliu sweet orange descends to about 50 % and the content of Red Anliu sweet orange keeps stable, but the content of citric acid in Anliu sweet orange is much more than that in its mutant at last. However, the contents of malic acid and quinic acid in the two materials showed no difference. The different content of sucrose is the major factor conferring the sugar difference between these two cultivars, and fructose and glucose are also different in some dates. The content of sucrose is keeping at 30.000 mg/g-35.000 mg/g in Red Anliu sweet orange, but the content of sucrose is much lower at about 20.000 mg/g-25.000 mg/g in Anliu sweet orange. The other two major sugars, fructose and glucose in juice sac are not so different before ripeness between two cultivars, but there are different in autumn because of their increase.3. Through the analysis of major organic acids and sugars in three parts of the fruit: the flavedo, albedo and segement membrane, we found that: the content of citric acid in segement membrane was the major different of organic acid between these two materials, the fruit of Anliu sweet orange had a high level content of citric acid, but much lower in albedo and flavedo. In the fruit of Red Anliu sweet orange, the content of citric acid was at a low level, less than 2.000 mg/g. In all three parts, the major difference in sugar content between two cultivars was in the content of sucrose; the sucrose content of Red Anliu in all three parts is higher than that in the fruit of Anliu sweet orange. But, the trend of the sucrose change was similar between the same parts of two cultivars, the content of sucrose in juice sac kept steady and increased in segment membrane, albedo and flavedo throughout the fruit development.All the results showed that the main difference of organic acid between two cultivars was in the content of citric acid, and sucrose is the main factor in forepart, but in autumn, sucrose, fructose and glucose are effective together. The fruit of Red Anliu sweet orange had a much lower level of citric acid content and higher level of sugars content than that of Anliu sweet orange. And these differences led to different flavor and taste of these two cultivars.
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