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Super/subcritical fluid extraction combined with ultrasound-assisted ethanol extraction in propolis development

Propolis has attracted commercial interest as a good source of flavonoids and terpenes. This study applied a two-step sequential extraction process, consisting of a super/subcritical extraction step and an ultrasound-assisted ethanol extraction (UAEE) step to raw propolis. The yields of propolis extracts and the extraction rates of flavonoids and terpenes have been used to evaluate the different extraction methods. The results have indicated that the yields of propolis extracts, total flavonoids, and eight characteristic flavonoids from subcritical fluid extraction (SFE) were much higher than the yields from supercritical CO2 extraction (SC-CO2), especially when the subcritical mixed-fluids extraction (SMFE) and subcritical subsection extraction (SSE) techniques were used. However, the extraction rate of terpenes from subcritical propane extraction (SPE) was obviously higher than the rates obtained with the other techniques. Furthermore, compared with the ethanol extracts of the super/subcritical raffinates, there is still a considerable amount of flavonoids in SPE raffinates (at 114.48 mg/g raffinate). SMFE and SSE can achieve efficient extraction of flavonoids, but synchronous extraction of terpenes and flavonoids can be achieved via two-step sequential extraction with SPE and UAEE. These findings provide a solid theoretical foundation for the effective extraction of propolis.