Green extraction of total flavonoids (TF) from Citrus pericarp using novel air nanobubbles (NBs) stabilized with biosurfactants assisted by ultrasonic disruption (UD)

• A novel device was assembled to establish a green extraction approach. • Biosurfactants can stabilize air nanobubbles for green extraction. • Nanobubbles assisted by ultrasonic disruption could improve flavonoids extraction. • Optimal extraction conditions for‘Chazhigan’ peel totoal flavonoids were validated. In this study, air nanobubbles (NBs) generated with a new device were stabilised by a complex of arabic gum (AG) and stevioside (STE). Some basic metrics of NBs produced by biosurfactants at different concentrations were characterized to determine the stability of NBs. The mixture solution rich in NBs was assisted by ultrasonic disruption (UD) to extract total phenols (TP) and total flavonoids (TF) from 7 citrus pericarp. We evaluated four key factors affecting the TF extraction of ‘ Citrus reticulata 'Chachiensis '’ (‘Chazhigan’) pericarp by one-way test. The optimal extraction conditions were further predicted and validated by Box-Behnken response surface experiments. Under the conditions of 135 w capacity, 4.1 C mixture solution concentration, 30.5°C water bath temperature, and 31min ultrasonic time, the TF content of ‘Chazhigan’ pericarp (20.82±0.85 mg/g DW) was significantly better than that extracted by 80% ethanol (12.22±0.90 mg/g DW). Finally, fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilised to provide a preliminary exploration of the potential mechanisms involved in the extraction process. The flavonoid extracts from the pericarp of ‘Chazhigan’ were qualitatively analysed. And the differences in the chemical antioxidant activity of their extracts were investigated before and after the application of traditional alcoholic extraction and novel green extraction. In conclusion, this study established a novel approach that is eco-friendly, which could effectively extract flavonoids from citrus peels.