Characterization of antioxidant compounds extracted from Citrus reticulata cv. Chachiensis using UPLC-Q-TOF-MS/MS, FT-IR and scanning electron microscope

•An optimized ultrasound method is useful for the extraction of bioactive compounds from Citrus reticulata cv. Chachiensis.•Total phenols, total flavonoids and antioxidant activity were evaluated as responses.•The ethanol concentration, ultrasound time and amplitude had a significant impact on extraction efficiency.•Fifty-five compounds were identified or tentatively identified by UPLC-QTOF-MS/MS.•The extract was characterized by Fourier transform infrared spectra and scanning electron microscopy.