The Phenolic Compounds, Metabolites, and Antioxidant Activity of Propolis Extracted by Ultrasound-Assisted Method

The influences of ultrasound-assisted, pharmacopeia, and supercritical fluid extraction methods on bioactive compounds and biological activities of propolis were evaluated. Results showed that propolis extracted by ultrasound-assisted method contained more phenolic compounds, and showed the highest total phenolic content (245.84 ± 6.41 mg GAE/g DW), total flavonoids content (198.82 ± 5.74 mg RE/g DW), and stronger in vitro antioxidant activity (DPPH·: 1.03 ± 0.04 mmol Trolox/g DW, ABTS+·: 2.19 ± 0.05 mmol Trolox/g DW, and FRAP: 1.48 ± 0.12 mmol FeSO₄ /g DW) than those of pharmacopoeia and supercritical fluid methods. A total of 36 phenolic compounds were identified in propolis. Among them, quercetin, quercetin-3-methyl-ether, kaempferol, isorhamnetin, luteolin-methyl-ether, and quercetin-7-methyl-ether could only be found in ultrasound-assisted and pharmacopoeia methods. Moreover, the phenolic compounds had the similar metabolic pathways in rats and were mainly metabolized by sulfation and glucuronidation pathways. Additionally, ultrasonic-treated propolis have good in vivo antioxidant activity and could repair D-galactose-induced oxidative damage in rats. Therefore, ultrasound-assisted method could replace pharmacopeia method to be considered as bioactive compounds extraction from propolis, taking into consideration of yield, short extraction time, and high antioxidant activity.