Optimization of phenolic compound extraction from raw arabica coffee beans using natural deep eutectic solvents

Raw Arabica coffee beans (RACB) contain large amounts of phenolic compounds, which have high antioxidant activity. Although there are few studies on natural deep eutectic solvents (NADES) for RACB, they show promising results for the extraction of phenolic compounds. With this in mind, we investigated 4 combinations of NADES to identify the optimal conditions for maximizing the extraction of phenolic compounds from RACB. Citric acid with glucose (2:1 M) or glycerol (1:1 M) and glucose with glycerol (1:2 M or 1:1 M) were prepared in a hot bath (50 ºC) under agitation with 30% of distilled water until dissolved. RACB ground (0,2 g) and 20 mL of NADES were put in an ultrasound bath for 75 min, and vacuum filtered. An extract made with 70% ethanol previously optimized was used for comparison. For solvents and extracts, Total Polyphenol Content (TPC) was measured by the Folin-Ciocalteu method, and antioxidant activity (AA) by the DPPH and FRAP methods. Solvents results were subtracted, once compounds of NADES presented AA. Extracts with acid citric in NADES composition presented the best results compared to ethanol 70%, mainly in AA (TPC 803.70±17.11, 648.27±6.90 and 695.52±26.67 mg CAE/L; DPPH 2504.18±107.29, 3177.68±144.68 and 1773.11±93.41 µMol TE/L; FRAP 8476.36±188.01, 8281.49±98.91 and 5282.77±297.66 µMol TE/L, respectively for citric acid with glucose (2:1 M) or glycerol (1:1 M) and ethanol 70%). The results for glucose with glycerol at a 1:2 M ratio were statistically equivalent to 70% ethanol, and 1:1 M presented the worst results (TPC 760.43±20.99 and 558.30±31.79 mg CAE/L; DPPH 2275.33±48.07 and 1950.89±117.44 µMol TE/L; FRAP 5573.79±44.41 and 5886.10±132.64 µMol TE/L, respectively for glucose with glycerol 1:2 M or 1:1 M). NADES containing citric acid were able to extract more total polyphenols of RACB and exhibited higher antioxidant activity.