Extraction, analysis of antioxidant activities and structural characteristics of flavonoids in fruits of Diospyros lotus L.

Flavonoid compounds are considered important components of new sources of natural antioxidants. This study was performed to optimize the ultrasound-assisted extraction processes of flavonoids from date plum persimmon (DPP) fruits, along with the in vitro antioxidant capacities and identities of those components. First, the effects of liquid/solid ratio, ethanol concentration, extraction time, and extraction temperature on flavonoid yields were investigated by independent variables analysis. Then the response surface methodology was used to optimize the extraction process, and the maximum flavonoid content was 3.05 ± 0.03 mg/g DW under the conditions of liquid/solid ratio 27:1 (mL/g), 74 mL ethanol/100 mL, extraction time 27 min, and extraction temperature 80 °C. Moreover, by DPPH and ABTS assays, the crude extracts of flavonoids in DPP fruits exhibited robust scavenging capacities with IC 50 values of 1.76 and 0.82 μg/mL, respectively. In addition, 17 bioactive compounds of DPP were isolated and identified by HPLC-ESI-QTOF-MS/MS, among which two were phenolic acid derivatives, two were flavanones, eight were flavones, four were pentacyclic triterpenoids and one was xanthone. This study provided information regarding the phytochemical composition and functional properties of DPP fruits, supporting future research to facilitate the development and utilization of DPP as a functional food.