Evaluation of the efficacy of green solvents in ultrasound assisted extraction of propolis bioactive components

Propolis is bee product that has been used in folk medicine for centuries due to their rich bioactive content. However, propolis is not suitable for raw consumption due to their resinous structure, low water solubility, strong taste, and odor. Thus, propolis must be extracted using different organic solvents, like ethanol, before consumption. Today, deep eutectic solvents, which are called environmentally friendly and recyclable green solvents, have been widely used especially in the extraction of bioactive compounds. In this study, propolis bioactive compounds were extracted using ultrasound assisted deep eutectic solvent extraction method. Ultrasound assisted extraction was carried out at 1:300 g/mL solid solvent ratio, 50°C temperature and 100% amplitude conditions for 45 minutes. The extraction of propolis was carried out 12 different deep eutectic solvents and ethanol (%90) to evaluate and compare extraction efficiency. Total phenolic content, total flavonoid amount, antioxidant activity, and antimicrobial activity values were determined to compare the effectiveness of propolis extractions carried out with different selected solvents. The citric acid-propanediol extract had the greatest total phenolic content (169.71±5.28 mg GAE/g) and total flavonoid content (129.53±1.50 mg CE/g) among the extracts obtained using deep eutectic solvents. The highest antioxidant activity (424.45±11.11 µmol TEAC/g) was obtained in the extract using lactic acid-propanediol (1:4). The total phenolic content was 228.19±0.70 mg GAE/g, the total flavonoid content was 221.57±2.86 mg CE/g, and the antioxidant activity was 580.34±23.18 µmol TEAC/g in the propolis sample extracted with ethanol. The major phenolic compound was caffeic acid in extracts obtained by ethanol and lactic acid-propanediol extraction, while the major phenolic was ferulic acid in extract obtained by citric acid-propanediol extraction. Furthermore, it was determined that propolis extracts obtained with citric acid-propanediol and lactic acid-propanediol have antimicrobial activity on Escherichia coli (15 and 10 mm/10 µL, respectively) and Staphylococcus aureus (13 and 11 mm/10 µL, respectively). The results show that the deep eutectic solvents used in the extraction have a significant effect on the antioxidant activity, total phenolic and flavonoid content (p<0.05). In conclusion, the citric acid-propanediol (1:4) and lactic acid-propanediol (1:4) may be used as an environmentally friendly alternative for propolis extraction.