Applications of Deep Eutectic Solvents in the Recovery of Bioactive Compounds from Brewer Spent Grains

Brewers' spent grain is known as the main by-product obtained during the initial stage of brewing, accounting for 85% of the overall solid by-product from the process. This material contains valuable components, including lignocellulose, proteins, lipids, minerals, vitamins, and phenolic compounds. To recover these constituents, various extraction techniques have been used. Deep Eutectic Solvents (DES) are an emerging group of green solvents utilized for the extraction of organic compounds from biomasses. DES is composed of two or more compounds that act as hydrogen bond acceptors and hydrogen bond donors. Choline chloride is mostly used as a hydrogen bond acceptor in combination with several hydrogen bond donors. While many methods can be used to prepare the solvents, heating with continuous stirring at approximately 50-80 degrees C is the most common technique. To improve extraction efficiency, the physicochemical properties of solvent mixtures need to be considered, such as the composition of those solvents, viscosity, polarity, and molar ratio of solvents. Extraction time and temperature, solid-to-liquid ratio, and water content, are also important. This review intends to present information on deep eutectic solvents and their current application in extracting brewers' spent grain.