Natural Deep Eutectic Solvents and Microwave-Assisted Green Extraction for Efficient Recovery of Bioactive Compounds from By-Products of Date Fruit (Phoenix dactylifera L.) Processing: Modeling, Optimization, and Phenolic Characterization

In this study, eight different natural deep eutectic solvents (NADESs) were utilized in combination with microwave-assisted extraction (MAE) as a green technique for the optimal extraction and achieve enhanced antioxidant activity of bioactive compounds from date seed powder (DSP). The two most efficient NADESs (choline chloride-lactic acid (ChCl-LA) and choline chloride-xylose (ChCl-Xylo) were further optimized for (MAE) using response surface methodology (RSM). Three factors considered for optimization were temperature (20, 55, and 80 ℃), irradiation time (5, 12.5, and 20 min), and percentage NADES contents (25, 55, and 85%). Total phenolic compounds (TPC), ferric reducing antioxidant power (FRAP), and 1,1-diphenyl-2-picrylhydrazyl (DPPH) activity were used as response factors. The optimal conditions were temperature (80 °C), irradiation time (5 min), and NADES contents (63%) for ChCl-LA, and temperature (80 °C), irradiation time (20 min), and NADES contents (50%) for ChCl-Xylo, respectively. At the optimized conditions, the highest values for FRAP, DPPH, and TPC obtained were 771.54 and 734.34 mM TE/g powder, 503.75 and 396.73 mM TE/g powder, and 147.92 and 234.65 mg GAE/g powder respectively, for ChCl-LA and ChCl-Xylo. The main phenolic compounds found in the selected extracts were catechin, 3,4-dihydroxybenzoic acid, and caffeic acid. This study infers that the utilization of MAE with appropriate NADESs as green extraction approach under optimized conditions can produce enhanced yield of bioactive compounds from date seeds. The synthesized NADES after appropriate toxicity studies could be used in replacement of conventional solvents which could be utilized in the food, pharmaceutical, and cosmetic industry as green and safe ingredients.