Inclusion complexes of trans-iso-alpha-acids with beta-cyclodextrin : preparation of highly enriched cis- and trans-iso-alpha-acids

Abstract

Separation of cis-iso-alpha-acids from trans-iso-alpha-acids, starting from the commercial isomerised hop extract, was successfully carried out by complex formation of the trans-iso-alpha-acids with beta-cyclodextrin. The separation was performed on laboratory scale permitting the quantitative dosage of cis-iso-alpha-acids resp. trans-iso-alpha-acids to 50 L of fermented beer, addition rate 25 mg/L. The methodology consists of two successive complex formation steps with a saturated solution of beta-CD in water. The precipitate from the first complex formation step is enriched in trans-isomers, which can be recovered from the beta-CD inclusion complexes. The collected first supernatant is already enriched in cis-isomers, but in order to obtain a higher enrichment in cis-isomers in this fraction, it was incubated again with beta-CD for a second complex formation step. The cis-isomers were then isolated from the second supernatant by solid phase extraction. The final cis-and trans-isomers fractions were highly enriched in respectively cis-iso-alpha-acids (98 %) and trans-iso-alpha-acids (90 %), as opposed to common isomerised hop extracts with a typical ratio of 70 % cis-iso-alpha-acids and 30 % trans-iso-alpha-acids. The established methodology for the isolation of cis-iso-alpha-acids and trans-iso-alpha-acids from a commercial isomerised hop extract allows highly advanced beer bittering on pilot scale and represents an innovative tool to further investigate both the cis-and trans-specific bitter acids degradation in beer in relation to flavour stability