Green Extraction of Greek Propolis Using Natural Deep Eutectic Solvents (NADES) and Incorporation of the NADES-Extracts in Cosmetic Formulation

In this work, a greener approach for the extraction of Greek propolis using ultrasound-assisted extraction method in combination with Natural Deep Eutectic Solvents (NADES) is presented. Propolis is a natural material of outmost interest as it possesses various biological and pharmacological activities and is therefore used for the manufacturing of extracts useful to various fields, such as pharmaceutics, cosmetics etc. Herein, five NADES were task-specifically selected as appropriate extraction solvents since they provide important assets to the final NADES-extracts, comparing to the conventionally used organic solvents. The screening study of the prepared solvents indicated the NADES L-proline/D,L-Lactic acid as the most effective medium for the raw propolis extraction due to the extract's high total phenolic content as well as its' significantly higher antioxidant activity. Then, the extraction using the selected NADES, was optimized by performing Experimental Design to study the effect of extraction time, propolis-to-solvent ratio and the %NADES content in the NADES-water system. All the extracts were characterized regarding their antioxidant activity and total phenolic content. The optimum NADES-extract as well as an extract derived by extraction using a conventional hydroethanolic solution were further characterized by performing LC/MS/MS analysis. The results showed that the NADES-extracts composition was similar or superior to the hydroethanolic extracts regarding the presence of valuable phytochemicals such as apigenin, naringenin etc. A disadvantage that is usually mentioned in the literature regarding the extractions using NADES is that the extracted bioactive compounds cannot be easily separated from the NADES in order to obtain dry extracts. However, this drawback can be converted to an asset as the task-specifically designed NADES that are used in this study add value to the end product and the optimum as-obtained NADES-extract has been successfully incorporated in a cosmetic cream formulation. In this work, The antioxidant activity and organoleptic characteristics of the cream formulation were also determined.