Choline Chloride-Based Deep Eutectic Solvents for Efficient Polyphenol Extraction from White Mulberry (Morus alba)

The efficiency of six deep eutectic solvents (DESs) based on choline chloride (ChCl) and various hydrogen bond donors (HBDs) was evaluated against a traditional organic solvent for extracting polyphenolic bioactive compounds from three different white mulberry samples (Morus alba), including branches, leaves, and fruits. Ultrasound-assisted extraction was performed under selected conditions identified for ChCl/glycerol DES: a 1:2 molar ratio of hydrogen bond acceptor to HBD, 20% water added to the DES, a temperature of 80 °C, and an extraction time of 30 min, providing a set of standard parameters for comparing the efficiency of different DESs. Extraction efficiencies were assessed using a developed and validated HPLC method, as well as total phenolic content and total flavonoid content assays. Among the tested DESs, those composed of ChCl and polyalcohols as HBDs showed the best performance. For branch and leaf samples, the ChCl/glycerol DES was the most effective, while for fruit samples, the ChCl/ethylene glycol DES showed the highest efficiency. In most polyphenol extractions tested, at least one DES achieved extraction efficiencies comparable to or higher than those obtained with methanol, except for flavonoids, for which DES yields were often lower. Overall, the results indicate that using DESs represents a greener and more sustainable approach to extracting bioactive compounds from white mulberry.