Preparation of Aqueous Propolis Extracts Applying Microwave-Assisted Extraction

Water-based propolis extracts usually contain up to 10-fold lower quantities of active ingredients due to poor solubility in water of propolis bioactive compounds when compared with ethanol-based extracts. Since ethanol-based extracts are of limited use, water-based extracts are preferred nowadays. The application of alternative extraction techniques should be evaluated to improve extraction efficiency. Aqueous propolis extracts were prepared using purified water and propylene glycol, 2-hydroxypropyl-beta-cyclodextrin and sodium bicarbonate aqueous solutions. A microwave-assisted extraction method was applied in cycles. The total concentration of hydroxycinnamic acids in aqueous propolis extract produced by four extraction cycles was determined to be 1502.1 ± 130.1 μg/mL and 20% propylene glycol, 10% 2-hydroxypropyl-beta-cyclodextrin and 5% sodium bicarbonate aqueous solutions, increasing the total concentration of hydroxycinnamic acids by 1.6, 1.7 and 1.9-fold, respectively. An application of microwave-assisted extraction method and the procedure of repeating extraction cycles reliably increased the quantity of hydroxycinnamic acids in aqueous propolis extracts. Similarly, the presence of propylene glycol, 2-hydroxypropyl-β-cyclodextrin and sodium bicarbonate increased the concentration of the hydroxycinnamic acids in propolis extracts.