Abstract: 【Objective】 To provide novel objective evaluation methods for the judgment of fruit maturation and its internal quality, the changes of polar metabolites in Guoqing No.1 satsuma mandarin (Citrus unshiu Marc. cv.Guoqing No.1) was investigated during fruit ripening. 【Method】 Extraction and analysis methods of citrus primary metabolites were established by using gas chromatography-mass spectrometry (GC-MS). Based on the method, polar metabolites in Guoqing No.1 satsuma mandarin at three different ripening stages (mature green, color-change and maturation stage) were assayed, and principal component analysis (PCA) was employed to explore the polar metabolite profiles.【Result】A total of 37 kinds of metabolites were identified. As the fruits turned orange, the levels of fructose, mannose and most amino acids (especially GABA and proline) in flavedo increased significantly, meanwhile, citric acid and some fatty acids decreased gradually. However, fewer metabolites changed in pulp during the processes. The contents of mannose, arabinose, oxalic acid, phosphoric acid, succinic acid, 2-keto-glutaric acid, 9,12-octadecadienoic acid, octadecanoic acid, palmitic acid and tetradecanoic acid reached the highest level at mature green stage and subsequent decreased gradually, while the content of sucrose, GABA and a variety of organic acids were largely accumulated. PCA results showed that polar metabolites in different tissues and ripening stages were separated very well in two dimensions.【Conclusion】 The results demonstrated that, with orange color enhancement, polar metabolites in citrus fruit changed dramatically. Moreover, the changes of these polar metabolites, especially sugars and organic acids, showed obvious tissue specificity, and some polar metabolites could be regarded as standards for citrus maturity index.

Key words: Citrus, fruit maturation, GC-MS, polar metabolites, metabolomics