Extraction of Plant and Algal Polyphenols Using Eutectic Solvents

Natural ingredients are currently attracting growing interest for industrial applications such as functional food, nutraceuticals, cosmetics, and pharmaceuticals. A key point is the societal acceptance for the naturally occurring compounds which are believed to be safer to humans and environment than artificial compounds. Polyphenols are one of the most interesting plant substances which are carrying many biological activities. Thousands of phenolic compounds have been identified, isolated, and selected from the plant kingdom including terrestrial and marine sources. A challenge concerns the development of efficient and green technologies for the extraction of plant and algal polyphenols. Ionic liquids have been successfully evaluated, but they are facing strong issues related to their cost, sourcing, and green nature, precluding any industrial development. Being cheaper and eco-friendly, deep eutectic and natural deep eutectic solvents have a great potential as solvents for the extraction of polyphenols. The ability of deep eutectics to form hydrogen bonds is particularly of interest for the selective extraction of polyphenols since these compounds are generally rich in hydrogen bond donor groups.Here we propose a comprehensive review of the use of deep eutectic solvent for polyphenol extraction processes, with more than 100 references published over the last decade. Despite the large possible combination of components for preparing deep eutectics with tunable properties, choline chloride-based eutectics are the most largely used extractant media. Important parameters including sampling, sample preparation, water content in deep eutectic solvent, extraction duration, and temperature along with methodology to account with all these interacting parameters are examined. These parameters have been put in perspective with extraction technologies. All are specifically considered in terms of extraction performances when using deep eutectic solvents. Here again, it turns out that only a few of the available technologies have been indeed evaluated with deep eutectic solvents, leaving ample perspectives for improvement in the field of polyphenol extraction in the near future. Finally, identification and quantification technologies are also discussed since they are also a key aspect in the process. The possibility of using deep eutectic solvents for a given application without having to extract the polyphenols also appears to be a very promising prospect, strengthened by the longer preservation of their antioxidant properties in deep eutectics.