Hae Choi, Leiden University, the Netherlands, and colleagues recently discovered so called natural deep eutectic solvents (NADES). These are natural ionic liquids (ILs) and deep eutectic solvents (DES) composed of natural compounds. Apart from sharing advantages of reported ILs and DES, NADES possess better properties for extraction, e.g., liquid state even below 0 °C, adjustable viscosity, and sustainability, they contain components that are abundant in our daily food, being thus cheap, sustainable, and safe; and some show a very high solubilization ability of both nonpolar and polar compounds. Moreover, they have proved to be able to dissolve even macromolecules.

The team investigated a wide range of NADES for the extraction of phenolic compounds of diverse polarity. They used safflower as a case study because its aromatic pigments cover a wide range of polarities.
Powdered safflowers were added to different NADES. The mixtures were gently heated and stirred for an hour. The extracts were purified with high-performance liquid chromatography and the isolated compounds identified with NMR and MS.
The extractability of both polar and less polar metabolites was greater with NADES than with conventional solvents. The water content in NADES proved to have the biggest effect on the yield of phenolic compounds. Most major phenolic compounds were recovered from NADES with a yield between 75 and 97 %. Most promisingly, one NADES containing proline and malic acid extracted 8 % more hydroxysafflor yellow A – a pharmacologically active pigment in safflowers – than a 40 % ethanol solution.

This holds promise for further applications of NADES in pharmaceutical, cosmetics, and food industries for the extraction and recovery of natural products.

• Natural Deep Eutectic Solvents as a New Extraction Media for Phenolic Metabolites in Carthamus tinctorius L.,
  Yuntao Dai, Geert-Jan Witkamp, Robert Verpoorte, Young Hae Choi,
  Anal. Chem. 2013.
  DOI: 10.1021/ac400432p