Ultrasonic assisted extraction of water-soluble vitamins from minor components of bee pollen with deep eutectic solvents (DESs) as green solvent

In this study, different deep eutectic solvents (DESs) were used for vitamin extraction from bee pollen. The DES combination with the highest total amount of individual vitamins was choline chloride: ethylene glycol (molar ratio 1:2). The response surface method was then used to optimize the extraction conditions. The independent variables used for optimization were ultrasonic power, time, and temperature, while the dependent variables were the total individual amino acids, total individual phenolic compounds, and total individual vitamin contents. Spectrophotometric analyses and antimicrobial activity were also determined in the extracts. In addition, AGREEprep, ComplexGAPI and BAGI tools were used to evaluate the greenness of the method. The results obtained with DES were compared with water, ethanol, and methanol extracts, which were considered control groups. As a result of optimization, the optimum conditions were found to be 75 % for ultrasonic power, 71.5 min for sonication time, and 40 °C for ultrasonic bath temperature. The model's composite desirability value (d) was found to be 0.81. The predicted value and the experimental values were close to each other. Furthermore, the most dominant vitamin in DES extracts was ascorbic acid, the most dominant amino acid was proline, and the most dominant phenolic compound was myricetin. The amounts of these compounds were higher than those obtained from water, ethanol, and methanol extracts. The spectrophotometric analysis results obtained higher yields with DES compared to the control groups. Antimicrobial activity analysis showed that pollen extracts prepared using choline chloride: ethylene glycol had a weak inhibitory effect for Gram-positive and Gram-negative bacteria but not yeast-like fungal strains. In conclusion, DES has been successfully used to extract vitamins and other bioactive compounds from bee pollen. The results obtained showed that DESs can be an alternative to organic solvents for the extraction of vitamins, which are among the minor components of bee pollen. Besides, the potential of the application different DESs for more efficient extraction of vitamins and components with important pharmaceutical properties from bee pollen needs to be evaluated in detail.