Supercritical fluid extraction of α- and β-acids from hops compared to cyclically pressurized solid–liquid extraction

• α- and β- acids were extracted from hops by supercritical fluid extraction (SFE).
• Supercritical fluid extraction with carbon dioxide was compared to cyclically pressurized extraction.
• Compounds extracted from hops were analyzed by electro-kinetic capillary chromatography (MECK).
• Supercritical fluid extraction was modeled, and the extractive process was explained by hot ball diffusion (HBD).
• Extraction efficiency obtained through supercritical extraction was similar to that obtained with cyclically pressurized extraction.

In this paper, two solid–liquid extraction techniques, supercritical fluid extraction (SFE) with and without modifiers and cyclically pressurized solid–liquid extraction with a Naviglio Extractor, were compared on the basis of extraction of acidic compounds contained in hops flowers. The hops extracts were analyzed by electro-kinetic capillary chromatography (MECK). The results showed that the technique using supercritical carbon dioxide was more effective for the isolation of β acids; the use of ethanol as a co-solvent, as reported in the literature, produced a heterogeneous extract, while cyclically pressurized solid–liquid extraction showed a greater extraction capacity for α acids. Consequently, both techniques are valid for the extraction of α and β acids from hops. By suitably varying the parameters of the two extractive procedures, it will be possible to obtain extracts for use in the production of beer and dietary supplements and drugs. Furthermore, based on the SFE CO2 extraction process, a mathematical model was applied to the examined process, and a numerical simulation was performed, leading to a model that provides direction for the optimization of further experiments.

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