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Inclusion complexes of trans-iso-α-acids with β-cyclodextrin: preparation of highly enriched cis- and trans-iso-α-acids
De Clippeleer, J., Van Opstaele, F., De Cooman, L. and Aerts, G.

Separation of cis-iso-α-acids from trans-iso-α-acids, starting from the commercial isomerised hop extract, was successfully carried out by complex formation of the trans-iso-α-acids with β-cyclodextrin. The separation was performed on laboratory scale permitting the quantitative dosage of cis-iso-α-acids resp. trans-iso-α-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 β-CD in water. The precipitate from the first complex formation step is enriched in trans-isomers, which can be recovered from the β-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 β-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-α-acids (98 %) and trans-iso-α-acids (90 %), as opposed to common isomerised hop extracts with a typical ratio of 70 % cis-iso-α-acids and 30 % trans-iso-α-acids. The established methodology for the isolation of cis-iso-α-acids and trans-iso-α-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 flavor stability.

Descriptors: hop bitter acids, isohumulones, cis-iso-α-acids, trans-iso-α-acids, isomerised hop extract, separation, cyclodextrin, inclusion complexes, enrichment

BrewingScience - Monatsschrift fr Brauwissenschaft, 69 (November/December 2016), pp. 128-141