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 °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 N2 added to the PLE system at 40 °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.