To investigate the effect of different doses of ⁶⁰Co-γ ray irradiation on the quality of ponkan peels, the major functional components of irradiated ponkan peels were determined by ultraviolet-visible (UV-Vis) spectrophotometry and high performance liquid chromatography (HPLC). The volatile components were analyzed qualitatively and quantitatively using headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). The results showed that irradiation affected the major functional constituents of ponkan peels. Treatment with a certain dose of irradiation increased the contents of total phenol, total flavonoid, nobiletin and tangeretin while decreasing the contents of hesperidin, gallic acid and ferulic acid, but had no significant effect on caffeic acid or chlorogenic acid. The irradiation treatment had a significant effect on the aroma constituents of ponkan peels, resulting in a decrease in the percentage, type and content of olefinic substances and an increase in the contents of alcohols, phenolic acids and aldehydes and ketones. Totally 51 new aroma substances were formed after irradiation treatment, and the odor activity value (OAV) showed that linalool, limonene and n-octanal were the key aroma substances of irradiated ponkan peels, indicating that ⁶⁰Co-γ ray treatment accelerated the aging of ponkan peels. In addition, principal component analysis (PCA) showed that the quality of ponkan peels varied with different irradiation doses, the highest overall evaluation score being observed for ponkan peels irradiated at 4 kGy. This study provides a reference for accelerating the aging of Pericarpium Citri Reticulatae as well as a basis for the development and utilization of Pericarpium Citri Reticulatae products.

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.