Extraction process, fraction characterization and in vitro bioactivity evaluation of flavonoids from Diaphragma juglandis fructus in Juglans sigillata.

In this study, total flavonoids were extracted from Diaphragma juglandis fructus (DJF) in Juglans sigillata via ultrasound-assisted extraction using a one-way test and response surface methodology. The optimum conditions for the extraction of flavonoids from DJF were as follows: ultrasound power, 160 W; extraction time, 39 min; liquid/solid ratio, 60 mL/g; extraction temperature, 51 °C; and ethanol concentration, 50 %. Extraction under these conditions provided a flavonoid yield of 11.45 %. Next, the obtained crude flavonoids were purified by macroporous resin to prepare 30 % ethanol-eluting fraction (DJF-1), 50 % ethanol-eluting fraction (DJF-2), and 70 % ethanol-eluting fraction (DJF-3). Fourier transform infrared (FTIR) spectroscopy revealed the characteristic peaks of flavonoids. Moreover, five flavonoids, namely, leucodelphinidin, 3,5,3'-trihydroxy-6,7,4'-trimethoxy flavone, (-)-phaseollidin, (-)-dihydrofisetin, and (-)-epicatechin-3-O-gallate (ECG), were initially identified via ultra-high performance liquid chromatography-tandem quadrupole time-of-flight secondary mass spectrometry (UPLC-Q-TOF-MS) analysis. In addition, the three DJF fractions exhibited good in vitro antioxidant, hypoglycemic, and hypolipidemic abilities. Among them, DJF-2 exhibited the strongest overall in vitro bioactivity due to galloyl and catechin structures derived from ECG.