Isolation of bitter acids from hops (Humulus lupulus L.) using countercurrent chromatography.

Dahlberg CJ1, Harris G, Urban J, Tripp ML, Bland JS, Carroll BJ. Author information: 1. Metagenics, Inc., Gig Harbor, WA 98332, USA.

Abstract

Commercially available hops (Humulus lupulus L.) bitter acid extracts contain a mixture of three major congeners (co-, n-, and ad-) in addition to cis/trans diastereomers for each congener. Individual isomerized α-acids were obtained by the consecutive application of two separate countercurrent chromatography methods. First, individual isomerized α-acid congeners as a mixture of cis/trans diastereomers were obtained using a solvent system consisting of hexane and aqueous buffer. The second purification, capable of separating cis/trans diastereomers, was accomplished using a quaternary solvent system; an alternative procedure using β-cyclodextrin followed by countercurrent chromatography was also investigated. The NaBH(4) reduction of the purified isomerized α-acid compounds followed by countercurrent chromatography purification resulted in individual ρ iso α-acids (>95%). Similarly, catalytic hydrogenation of the purified isomerized α-acid compounds followed by countercurrent chromatography purification produced individual tetrahydro isomerized α-acids (>95%). Reported herein is a widely applicable approach that focuses on three critical variables–solvent system composition, pH, and buffer-to-sample ratio–that enable the efficient purification of individual bitter acids (≥95%) from commercially available hops extracts. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. PMID: 22689494