Spent coffee grounds (SCGs) are viewed as a valuable resource for useful bioactive compounds, such as chlorogenic acids and flavonoids, and we suggest an eco-friendly and efficient valorization method. A series of choline chloride-based deep eutectic solvents (DESs) were tested as green extraction solvents for use with ultrasound-assisted extraction. Extraction efficiency was evaluated based on total phenolic content (TPC), total flavonoid content, total chlorogenic acids, and/or anti-oxidant activity. A binary DES named HC-6, which was composed of 1,6-hexanediol:choline chloride (molar ratio 7:1) was designed to produce the highest efficiency. Experimental conditions were screened and optimized for maximized efficiency using a two-level fractional factorial design and a central composite design, respectively. As a result, the proposed method presented significantly enhanced TPC and anti-oxidant activity. In addition, phenolic compounds could be easily recovered from extracts at high recovery yields (>90%) by adsorption chromatography.

Keywords

Spent coffee grounds; 
Deep eutectic solvents; 
Phenolic compounds; 
Anti-oxidant activity; 
Two-level fractional factorial design; 
Response surface methodology


… a purity of 98% except for 3-CQA (≥ 95%). 5-Caffeoylquinic acid (5-CQA; ≥ 98%)
was purchased from Chengdu Biopurify Phytochemicals Ltd. (Chengdu, Sichuan,
China). The compounds used to assess TPC, TFC, and anti …