Direct steam injection pretreatment improves microwave-assisted extraction yield for total flavonoids and myricetin from Hovenia dulcis Thunb

A direct steam injection pretreatment was added before the microwave-assisted extraction procedure for the extraction of flavonoids from seeds of Hovenia dulcis Thunb, and the antioxidant activity of flavonoid extracts was determined. Based on the experimental results, the addition of direct steam injection simultaneously increased the extraction yield of total flavonoids compared with direct microwave-assisted extraction, and antioxidant activity of flavonoid extracts obtained by adopting the steam injection pretreatment was higher than that by direct microwave extraction alone. Myricetin was isolated from the flavonoid extracts, and the structure was identified by infrared spectroscopy (IR), electrospray ionization mass spectrometry (ESI-MS), and 1H nuclear magnetic resonance (1H-NMR). Recovery yield of total flavonoids was increased by 11.63% when the direct steam injection pretreatment was added to direct microwave extraction.