Hops Humulus lupulus

Summary

Design

Five hop varieties — Brewer's Gold, Aroma, Magnum, Spalter Selekt and Traditional — were extracted with supercritical CO₂. Subcritical water extraction was then tried on the spent hops left after SFE, specifically to recover xanthohumol. The work targeted the bitter α- and β-acids (humulones and lupulones) and xanthohumol.

Sample preparation

Type 90 pellets were milled to a particle diameter of ≤1 mm. The moisture content of the pellets, determined gravimetrically, was ≤10 %, within the range required for SFE.

Extraction

Extractions ran on a SuperEx SC-1000 system with a 1 L vessel rated to 500 bar and 200 °C, the material loaded in a steel basket with 10 µm mesh filters. The raw material was heated to the setpoint and pressurised, then extracted in dynamic flow-through mode at constant CO₂ flow, with an automatic backpressure regulator settling the extract in the separator. Runs used pure CO₂ at 40 °C (CO₂ flow 100 mL min^-1 in the Brewer's Gold and Aroma runs; the Aroma run at 450 bar and the Brewer's Gold run at 300 bar began with a 15-minute static period). Brewer's Gold and Aroma were extracted at 300 bar and at 450 bar for 150 minutes each; Spalter Selekt and Traditional at 450 bar for 150 minutes; Magnum at 450 bar for 150 minutes and, to follow the progression of bitter-acid recovery, in a staged run of 60 minutes at 150 bar followed by 120 minutes at 300 bar. For fractionated runs separator 1 was held at 150 bar (40 °C, or −10 °C for wax precipitation); otherwise the extract was collected at 55 bar. Overall extraction curves (OEC) were constructed from the SFE data.

Downstream isolation and analysis

The α- and β-acids were isolated from the whole extract into an aqueous alkaline solution as potassium salts. Xanthohumol was recovered from the spent hops remaining after SFE, by subcritical water at 150 °C for 20 minutes (dynamic at 30 mL min^-1 and static modes) and by methanol extraction followed by column purification. Analytical samples (10.0–30.0 ± 0.1 mg, 189 in total) were diluted in pure methanol at 0.3–3.0 ± 0.1 mg mL^-1 for HPLC-DAD; essential oils were diluted 100-fold in hexane for GC-MS/FID.

Measured yields, compositions and chromatograms are reported in the full application note (PDF above).

At a glance

Plant material

Hops — Humulus lupulus

Target compounds

Xanthohumol, α-/β-acids, iso-α-acids, essential oil

Compound class

Polyphenols

Published

January 2025

Document

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