The impact of using an expansion gas with high-intensity ultrasound on the pressurized liquid extraction of bioactive compounds from an industrial coffee solid residue

This study proposes a new methodology employing pressurized liquid extraction (PLE) assisted by gas-expanded liquid extraction (GXE) and high-intensity ultrasound (HIUS) in-line with ultraviolet-visible spectrometry (UV-Vis) detection to obtain and analyze bioactive compounds from a coffee solid residue. The parameters evaluated for extracting the compounds were solvent (water, ethanol, and hydroethanolic mixtures), temperature (40, 80, and 120(degrees) C), pressure provided by GXE (0, 0.5, and 1 MPa), and HIUS application time (2, 6, and 10 min). Tested conditions provided an extract with four main compounds: peak 1 (5-caffeoylquinic acid isomer candidate), 5-caffeoylquinic acid, caffeine, and peak 4 (quinic acid derivative candidate). The solubility of 5-caffeoylquinic acid (5-CQA) and caffeine was assessed by evaluating their activity coefficients across different proportions of ethanol and water, ranging from 0% to 100%, with increments of 10% employing in silico analysis. However, experimental results have shown that water is equally efficient as the hydroethanolic mixture and even more efficient than ethanol in extracting these compounds. The N-2 added to the PLE system at 40(degrees )C favored the acoustic cavitation phenomenon increasing the extraction yield of 5-CQA isomer and 5-CQA by approximately 18 and 38%, respectively. In-line analysis was conducted using a UV-vis detector, while offline analysis was performed with ultra-high performance liquid chromatography with a photodiode array detector UPLC-PDA. Its comparison demonstrated that real-time (in-line) detections provided the most accurate qualitative extraction kinetic profile, as it considers the whole extract. Therefore, the coupling of extraction and analysis technologies enabled a faster process, ensuring a higher yield of bioactive compounds and their qualitative analysis using less solvent in a shorter time.