Simultaneous extraction, separation, and analysis of 5-caffeoylquinic acid and caffeine from coffee co-product by PLE-SPE × HPLC-PDA two-dimensional system

Abstract

This study proposed an integrated and automated procedure to extract, separate, and quantify bioactive compounds from a coffee co-product by pressurized liquid extraction (PLE) coupled inline with solid phase extraction (SPE) and online with HPLC-PDA (PLE-SPE × HPLC-PDA). The efficiency of the two-dimensional system in performing real-time analysis was verified by comparing HPLC-PDA results acquired by the system (online) and carried out after the extract fraction collection (offline). Different flow rates (1.5 mL/min for 336 min, 2 mL/min for 246.4 min, and 2.5 mL/min for 201.6 min) were evaluated to optimize the extraction, separation, and analysis method by PLE-SPE × HPLC-PDA. Subcritical water at 125 °C and 15 min of static time allowed the highest extraction yields of caffeine and 5-caffeoylquinic acid (5-CQA). Caffeine was retained during the aqueous extraction in the SPE adsorbent and eluted from the column by exchanging the solvent for a hydroethanolic mixture. Thus, caffeine was separated from 5-CQA and other phenolic compounds, producing extracts with different compositions. The solvent flow rate did not have a significant effect (p-value ≥ 0.05) on the extraction, separation, and analysis (by online and offline methods) of 5-CQA. However, the online quantification of retained compounds in the SPE (i.e., caffeine) can underestimate concentration compared to offline analysis. Nevertheless, the results suggest that coupling of advanced techniques can be used to efficiently extract, separate, and analyze fractions of phenolic compounds, supplying an integrated method to produce high-added value ingredients for several applications.

Keywords: Biorefinery; Coffee husk; Inline processes; Pressurized liquid extraction; Solid phase separation.