Selective extraction of phenolic compounds from barley waste using deep eutectic solvents

In this study, the development of an ultrasound method for extraction of phenolic compounds from barley waste using acidic deep eutectic solvents (UAE-DES) was investigated. Optimization of the extraction parameters, which include extraction time, temperature, and ultrasound power (UP), was performed using the One-Factor-at-a-Time (OFAT) experimental design, followed by HPLC-PDA for determination of total quantified phenolic content (TQPC). In addition, the influence of water addition on TQPC was evaluated. The Maximum TQPC obtained was 5.78 mg/g using ChCl: formic acid at a molar ratio (1:2) and optimal conditions of (70 °C, 30 min, 80% UP, 10% water), and 4.67 mg/g, using ChCl: tartaric acid at a molar ratio (1:2) and optimal conditions of (70 °C, 25 min, 100% UP, and 20% water). The obtained TQPC was 5- and 4-fold higher in comparison with 70% methanol and 70% ethanol extraction. LC–MS-qTOF analysis of DES extracts revealed diverse phenolic compounds, while the concentration range of compounds obtained was as follows: ferulic acid (0.86–2.47 mg/g), catechin (0.12–2.16 mg/g), p -coumaric acid (0.12–0.32 mg/g), naringenin (0.54–0.86 mg/g), and apigenin (0.15–0.91 mg/g). SEM analysis confirmed enhanced accessibility of lignocellulose in DES-treated samples. The sustainability of UAE-DES extraction was assessed using AGREE, AGREEprep, CACI, BAGI, and CaFRI green tools. The grade assessment of each tool resulted in scores: 0.63 for AGREE, 0.57 for AGREEprep, 65 for CACI, 82.5 for BAGI, and 72 for CaFRI, indicating a greener extraction performance of UAE-DES in comparison with 70% methanol and 70% ethanol extraction.