Isolation of bitter acids from hops (Humulus lupulus L.) using countercurrent chromatography.
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.
Metagenics, Inc., Gig Harbor, WA 98332, USA. clintondahlberg@metagenics.com
Clinton J
CJ
Dahlberg
Guy
G
Harris
Jan
J
Urban
Matthew L
ML
Tripp
Jeffrey S
JS
Bland
Brian J
BJ
Carroll
D000143:Acids / Q000737:chemistry / Q000302:isolation & purification*; D003377:Countercurrent Distribution / Q000379:methods*; D027582:Humulus / Q000737:chemistry*; D007536:Isomerism; D010936:Plant Extracts / Q000737:chemistry / Q000302:isolation & purification*
D000143:Acids; D010936:Plant Extracts