Use of natural deep eutectic solvent (NADES) as a green extraction of antioxidant polyphenols from strawberry tree fruit ( Arbutus unedo L.): An optimization study

Strawberry tree fruits ( Arbutus unedo L.) are being studied as an underutilized wild fruit, rich in various bioactive compounds, especially polyphenols. The main objective of this study was to optimize the extraction process using a natural deep eutectic solvent (NADES) to obtain the highest polyphenol content and antioxidant activity of strawberry tree fruits as determined by different in vitro assays (DPPH, FRAP and ABTS). For this purpose, extraction with NADES was performed in three steps. Among twenty different NADES systems screened for extraction in the first step of solvent screening, two solvents that gave the best results (N6: Betaine - glycer- ine - water with a molar ratio 1:2:1 and N9: Choline chloride - glycerine with a molar ratio 1:2) were screened in the next step. For these two solvents, two separate Face-centered central composite designs with S/L ratios (10 - 20-30 g NADES/g sample), temperature (40 - 55-70 degrees C), and extraction time (60 - 120-180 min) were used by response surface methodology (RSM), with total phenolic content and antioxidant activity as the target responses. Based on the software multi-response optimization prediction, the optimal conditions for N6 and N9 were: 1:30 S/L ratio, 65 degrees C temperature and an extraction time of 150 min, and 1:20 S/L ratio, 56 degrees C and 180 min, respectively. The optimal parameters were verified experimentally and the main polyphenols were quantified by HPLC-DAD.