Optimization, comparison and mechanism of ultrasound-assisted cellulase hydrolysis and ethanol extraction of quercetin, luteolin and apigenin from male inflorescences of Populus alba × berolinensis

In this study, we aimed to determine the optimal process parameters for extracting quercetin, luteolin and apigenin from the male inflorescences of Populus alba × berolinensis via the ultrasound-assisted cellulase hydrolysis and ethanol extraction (UACHEE) method and investigated the mechanism of cellulase action during the extraction process. The Box-Behnken design (BBD) was subsequently used to optimize the operating parameters. The optimal extraction parameters of ultrasound-assisted cellulase hydrolysis were as follows: ethanol volume fraction of 70 %, 40 mg/g of dose of cellulase, 50 °C of incubation temperature, 148 min of incubation time, pH of 5, mL/g of liquid‒solid ratio, duty cycle of 16.67 %, 200 W of ultrasound irradiation power in the incubation process, 200 W of ultrasound irradiation power in the extraction process, and 15 min of ultrasound irradiation time in the extraction process. Compared with other extraction methods, UACHEE presented an advantage in maintaining higher yields of quercetin, luteolin and apigenin (428.68, 549.65, 1136.20 μg/g). In addition, we used different characterization methods to clarify the extraction mechanism of this method to better improve the extraction yield and efficiency of the target components. This study will lay a theoretical foundation for the potential practical application of the male inflorescences of P. alba × berolinensis extracts in fields such as medicine, functional foods, cosmetics, environment and agriculture.