Propolis is a bioactive natural product produced by honeybees which is enriched in various phenolic compounds including flavonoids and phenolic acids and thus exerting the antioxidative activity. Ultrasound-assisted extraction is considered as a green and highly efficient method for bioactive components extraction from natural products. To obtain phenolic compounds from propolis with highly efficiency, ultrasound-assisted extraction was optimized. In this study, 80% ethanol was selected as the extraction solvent. Results showed that the optimum extraction conditions were as follows: the liquid to solid ratio was 60:1 (mL/g), ultrasonic power was 135 W, and ultrasonic time was 20 min. The highest total phenolic content and total flavonoid content were 48.25 ± 0.30 mg gallic acid/g and 211.00 ± 0.87 mg rutin/g, respectively. At the same time, the strongest anti-oxidant activities measured by 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and 2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging assay were obtained at the same optimal condition with values of 162.99 ± 0.35 mg trolox/g and 156.59 ±5.28 mg trolox/g, respectively, indicating that the total phenolic content and total flavonoid content contributed to the anti-oxidant activities. The content of five major flavonoids of propolis including galangin, chrysin, pinocembrin, pinobanksin and pinobanksin-3-acetate were increased by high performance liquid chromatography-quadrupole time of flight mass spectrometry analysis. As for the propolis structures, the Fourier-transform infrared spectroscopy analysis revealed that ultrasound-assisted extraction did not change the primary structure of propolis, while scanning electron microscope analysis showed that ultrasound-assisted extraction could enhance the contact area between propolis and ethanol. In summary, the ultrasound-assisted extraction increased the extraction yield of propolis with shorter extraction time, which is an ideal green extraction method for propolis extraction.

Ultrasonic-assisted extraction of chinese propolis: Optimization based on phenolic content, flavonoid content and antioxidant capacity

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