UPLC-QTOF-MS/MS screening and identification of bioactive compounds in fresh, aged, and browned Magnolia denudata flower extracts

The Magnolia denudata flower is used to prepare tea and is often fermented to improve its flavor. Herein, fresh, aged, and browned M. denudata flower extracts were characterized using ultra performance liquid chromatography coupled with a hybrid quadrupole orthogonal time-of-flight mass spectrometer (UPLC-Q-TOF/MS/MS). The 1223 and 458 mass ions of ESI+ and ESI- modes that were significantly changed by the fermentation process were selected using three criteria. Sixteen compounds including flavonoids, phenylethanoid glycoside derivatives (PhGs), caffeoylquinic acids (CQAs), and others were identified based on their accurate mass and MS/MS spectra and analyzed as the main chemical components. The levels of the main chemical components changed after fermentation. The comparative quantity and composition of the phytochemicals differed for the three extract types. For example, flavonols were affected by fermentation, resulting in an increase or decrease (fold change value of negative ion: rutin -0.47; keioside 1.00). The CQAs were low during fermentation (1-CQA, -1.62; chlorogenic acid, -1.48). However, the quinic acid content was significantly high (quinic acid, 1.36). Isomers of PhGs like isoverbasoside and isoacteoside were produced during fermentation (isoverbasoside, 5.42; isoacteoside, B 3.33). These observations may provide a basis for studying the physiological effects of non-fermented and fermented M. denudata flower.