Identification of the chemical compositions of Ponkan peel by ultra performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry

As one of the most widely consumed citrus fruits, Citrus reticulata Blanco cv. Ponkan is known to have a number of dietary and medicinal values. In this work, we developed a new method using ultra performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) for qualitative analysis and profiling of chemical compositions in Ponkan peel methanol extract. With this method, the elution and separation of chemical components in Ponkan peel could be easily completed within seven minutes. The method was much faster than other analytical methods previously used with citrus fruits. According to the chromatography retention time, UV spectrum, and exact molecular weight and high energy fragment ions combined with information from reference standards or literature, a total of 32 bioactive compounds were unambiguously identified or tentatively characterized in the Ponkan peel extract. The compounds included 8 flavonoid-O-glycosides, 5 flavone-C-glycosides, 1 dimethoxyflavone, 10 polymethoxyflavones and 8 other compounds. Among these compounds, caffeoyl-glucose, dihydrophaseic acid glycosil ester, ferulic acid hexose, luteolin-6,8-di-C-glucoside, luteolin-8-C-glucoside, narirutin 4'-glucoside, nomilinic acid glucoside, isolimonic acid, dihydroxy-dimethoxyflavone, and 5,7,4'-trimethoxyflavone were characterized for the first time in Ponkan peel to our knowledge. These results showed the UPLC-Q-TOF-MS was a powerful tool to analyze the structures of chemical compounds in Ponkan peel. And our data will provide useful information for further evaluating the bioactivity of Ponkan peel and the utilization of Ponkan resource.