Ultrasound-assisted extraction of Ehretia macrophylla wall. Fruit phenolic acids: Process optimization, characterization, and lung protective activities

Ehretia macrophylla Wall. fruit (EMF) is rich in phenolic acids and is commonly used as an ethnomedicine against respiratory diseases. In this study, ultrasound-assisted extraction (UAE) was employed to obtain the optimal extract of EMF phenolic acids (EMFPA). The chemical components of EMFPA were characterized, and its antioxidant, anti-inflammatory, and lung protective activities were systematically evaluated. Using a Box-Behnken response surface methodology design, the optimal UAE conditions were determined to be ultrasound power of 350 W, a time of 67 min, a temperature of 53℃, and a liquid-to-solid ratio of 45:1 mL/g, resulting in the highest extraction yield value of EMFPA (84.32 ± 0.21 mg CA/g), which was significantly higher than that obtained with ethanol reflux extraction (ERE). A total of 31 phenolic acids were identified in EMFPA by UPLC-Q-TOF/MS, including protocatechualdehyde, caffeic acid, and rosmarinic acid derivatives. Quantitative analysis revealed that UAE yielded higher major phenolic acids than ERE, especially salvianolic acid A. The antioxidant activity of UAE-EMFPA was substantially higher than that of the ERE-EMFPA, and the UAE-EMFPA had a concentration dependent inhibitory effect on NO, TNF-α, and IL-6 generation in the LPS-induced MLE-12 cell inflammatory model. Furthermore, EMFPA treatment markedly reduced the W/D ratio, alleviated inflammatory cell infiltration, and mitigated the histopathologic injuries in LPS-induced acute lung injury mouse model. These findings fully confirm that UAE is a superior method for EMFPA extraction, and that EMFPA is a potential natural active for developing lung-protective functional foods or pharmaceuticals.