Characterization of Polymethoxylated Flavonoids in the Peels of Chinese Wild Mandarin (Citrus reticulata Blanco) by UPLC-Q-TOF-MS/MS

Abstract

China is the most important origin center of the genus Citrus L., especially the wild mandarin (Citrus reticulata Blanco). The aim of this work was to systematically qualitative and quantitative analysis of polymethoxylated flavonoids (PMFs) in seven Chinese wild mandarin citrus using ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS/MS) and UPLC-photodiode array (UPLC-PDA) analyses. This method was validated including the linearity, limit of detection (LOD), limit of quantification (LOQ), precision, repeatability, stability, and recovery. The results demonstrated that UPLC-Q-TOF-MS/MS was a powerful tool to analyze the PMFs in wild citrus peel, and this method was trustable, rapid and sample. Besides, ten PMFs were identified or tentatively characterized as 5,6,7,3′,4′-pentamethoxyflavanone (1), isosinensetin (2), sinensetin (3), 5,7,3′,4′-tetramethoxyflavone (4), 3,5,7,4′-tetramethoxyflavone (5), nobiletin (6), 3,5,6,7,8,3′,4′-heptamethoxyflavone (7), 5,7,4′-trimethoxyflavone (8), 5-Hydroxy-6,7,8,3′,4′-pentamethoxyflavone (9), and tangeretin (10). Among these compounds, 4 was the first time to be identified in citrus. Then the contents of eight PMFs (2, 3, 4, 6, 7, 8, 9, and 10) in these samples were quantified. Compounds 3, 6, and 10 were found to be the prominent PMFs. Cupigoushigan had the highest contents of 3 (2.617 mg/g DW) and 6 (11.111 mg/g DW), and Dakengyeju had the highest content of 10 (5.560 mg/g DW). Our results indicated that wild mandarins are potentially rich source of Citrus PMFs for foods or other utilization.