Comparative Untargeted Metabolomics Analysis of the Peels of Citrus reticulata ‘Chachi’ and Different Varieties of Citrus unshiu Marc.

The metabolomic differences between the peels of Citrus reticulata ‘Chachi’ and different varieties of Citrus unshiu Marc. were analyzed to provide a theoretical basis and scientific evidence for the development and utilization of the peels of Citrus unshiu Marc.. The chemical composition of Citrus reticulata ‘Chachi’ (CZG) and three different varieties of Citrus unshiu Marc. (‘Youliang’ (YL), ‘Nangan 20’ (NG) and ‘Gongchuan’ (GC)) were determined by ultrahigh performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), and the metabolomic data were comparatively analyzed using principal component analysis (PCA), orthogonal partial least square-discriminant analysis (OPLS-DA) and cluster analysis (CA) to screen differential metabolites. Through database comparison, 790, 796 and 818 metabolites were identified between CZG and YL, NG and GC, respectively, with organic oxides, flavonoids, carboxylic acids and their derivatives accounting for the highest proportions, which are mainly involved in the metabolic pathways of flavonoid and flavanol biosynthesis, isoflavones biosynthesis, α-linolenic acid metabolism, and phenylpropanoid biosynthesis. Using the cutoff of variable importance in the projection (VIP) score > 1 with P value < 0.05, stable and reliable differential metabolites were selected. A total of 43 differential metabolites of 11 classes were identified between Citrus reticulata ‘Chachi’ and Citrus unshiu Marc., the predominant ones being flavonoids, amino acids and purine nucleosides. Most flavonoids in Citrus unshiu Marc. such as 5,6,7,8,3’,4’,5’-heptamethoxyflavone, quercetin, naringenin, and naringenin were up-regulated, which could be used as potential markers to differentiate Citrus reticulata ‘Chachi’ from Citrus unshiu Marc.. Furthermore, Citrus unshiu Marc. had a higher content of flavonoids and therefore could be used as a source of Citri Reticulatae Pericarpium.