Synergistic combination of natural deep eutectic solvents and green extraction techniques for the valorization of date palm leaves: Optimization of the solvent-biomass interaction

This study was designed to explore date palm leaves as natural polyphenolics potential source using appropriate green Natural Deep Eutectic Solvent (NADES) and emerging green extraction technologies. Among the studied NADES, Glycerol-based NADES showed higher phenolics yield compared to saccharide and organic acid-based NADES. Experimental conditions for microwave (MAE)-NADES and ultrasonication (UAE)-NADES couplings were optimized using a 23-factorial design. Interestingly, it was found the UAE-NADES was not effective enough to enhance phenolics recovery, while MAE-NADES was significantly effective. Furthermore, MAE-NADES-based extracts portrayed higher bioactive properties compared to UAE-NADES-based extracts. Accordingly, MAENADES extraction parameters were further optimized using a Box-Behnken design of Response Surface Methodology (RSM). RSM predicted that MAE-NADES extraction can be maximized at a NADES concentration of 49 %, and power of 800 W for 0.84 min. The current study concludes that the application of MAE-NADES green extraction technology can be an effective approach for bioactive compounds recovery from date palm leaves. Industrial relevance: There are more than 120 million date palm trees in the world producing around 20-35 kg of leaves per palm tree annually. This is a huge burden on the environment and if explored as a potential source of polyphenols and other components may turn out to be a viable economic source for desert regions. During the last few decades, a special focus has been raised on ensuring that the extraction process is monitored in an economical and ecofriendly manner without downgrading the biological functionality of the resulting extracts. Recently, Natural Deep Eutectic Solvents (NADES) have been applied for the extraction of polyphenolic compounds. Moreover, the utilization of green extraction techniques, such as ultrasonication and microwave, have been extensively investigated for the extraction of bioactive compounds from plant-based matrices with promising future prospectus, in terms of the reduction in extraction time and higher recovery yields.