Formulation and characterization of betaine-based deep eutectic solvent for extraction phenolic compound from spent coffee grounds

Spent Coffee Ground (SCG) is one of the least processed domestic wastes in Indonesia, its low economic value is the main reason why this waste is not considered. Deep eutectic solvent (DES) is one of the newest, most efficient and environmentally friendly solvents, which is beginning to be widely studied as solvents for extraction of natural bioactive compounds. In this study a series of betaine based DESs was prepared by combining betaine as hydrogen bond acceptor (HBA) and diols (1,2 propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol and 1,3-butanediol), and acids (levulinic acid, lactic acid) as hydrogen bond donors (HBD). The extraction was carried out using green solvents with a thermo-shaker for 1 hour at 50°C and 550 rpm with a 1:10 mass ratio of solid to liquid. The efficiency of DES extraction was evaluated based on the total phenolic content (TPC) and anti-oxidant activity using Ultraviolet-Visible Spectrophotometry (UV-Vis). The 2,2-diphenyl-1-picrylhydrazyl (DPPH) and Folin-Ciocalteu reagent (FCR) were used in antioxidants and phenolic compounds assays. The results show the sequence of capabilities of DES extracting phenolic compounds from spent coffee ground is betaine - 1,2-butanediol > betaine-1,3-butanediol > betaine-1,3-propanediol > betaine- lactic acid > betaine-1,2-propanediol > betaine-Levulinic acid > betaine-1,4-butanediol > ethanol. The highest total phenolic content extracted was 31.67 mg GAE / g SCG using DES betaine-1,2-butanediol as solvent. The high antioxidant activities for DESs betaine-1,2-butanediol, betaine-1,3-butanediol and betaine-lactic acid were shown by low values of IC50 at a concentration below 1.6 ppm. The result shows that spent coffee ground, as a food waste, still contains valuable compounds that can be extracted and utilized. In addition, betaine based deep eutectic solvents as green solvents were proven to be able to extract valuable bioactive compounds from SCG.