Supercritical carbon dioxide extraction enhances flavonoids in water-soluble propolis

Abstract

Two propolis, obtained from Brazil and China, were ground and individually treated using supercritical carbon dioxide to enhance the extraction and water solubility of nine flavonoids. Co-solvent effects of ethanol and water were examined. Extractions were carried out semi-batchly at 5 mL/min CO2, at pressures ranging from 2000 to 5000 psig, at temperatures ranging from 35 to 65℃, and with propolis to co-solvent ratios of 1:2 and 1:5 (w/v). After supercritical extraction of 500 liters of CO2, the residual propolis in the extractor was further extracted by means of normal solvent extraction using 95% ethanol (ReE extract was obtained) and de-ionized water (ReW extract was obtained). Nine active propolis flavonoids in the extracts were analyzed to verify their inhibitory effects on leukemia cancer cells. Experimental results indicated that the dry SC-CO2 extract mainly contained low-polar wax-like materials. The crude yield of Brazilian propolis in the dry SC-CO2 extract reached around 10% at 45℃ and 4000 psig extraction. The amounts of the nine flavonoids in the Brazilian ReE and ReW extracts were 5% and 120%, higher than those obtained by means of conventional ethanol and water extraction, respectively. The Brazilian ReW extracts clearly contained a few water-soluble compounds and, especially, enhanced amounts of the nine flavonoids. All the extracts were tested for viability and cell proliferation of leukemia HL-60 and U937 cancer cells, and most exhibited a postivie inhibitory effect. The results also suggested that something other than the nine flavonoids in dry SC-CO2 extract was importantly involved in the inhibitory effect.