title: Oxidation of isohumulones induces the formation of carboxylic acids by hydrolytic cleavage.
abstract: The degradation of isohumulones in mechanistic experiments was investigated. Incubation of trans-isohumulone in the presence of l-proline led to the formation of carboxylic acids and their corresponding proline amides. In the context of isohumulones unknown amides were verified first in model incubations and then in beer for the first time by comparison with authentic reference standards via LC-MS analyses. Carboxylic acids and amides were formed preferably under oxidative conditions and increasing pH. Stable isotope experiments excluded the incorporation of molecular oxygen into carboxylic acids, strongly indicating a hydrolytic mechanism via β-dicarbonyl cleavage. The proposed mechanism includes oxidation and thereby incorporation of molecular oxygen to the isohumulone ring structure followed by hydrolytic cleavage leading to acids and amides.
authors.affiliation: Institute of Chemistry, Food Chemistry, Martin-Luther-University Halle-Wittenberg , Kurt-Mothes-Straße 2, 06120 Halle/Saale, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Rakete
authors.forename: Robert
authors.initials: R
authors.lastname: Berger
authors.forename: Steffi
authors.initials: S
authors.lastname: Böhme
authors.forename: Marcus A
authors.initials: MA
authors.lastname: Glomb
mesh_terms: D000577:Amides / Q000737:chemistry; D001515:Beer / Q000032:analysis; D002264:Carboxylic Acids / Q000737:chemistry*; D002853:Chromatography, Liquid; D003517:Cyclopentanes / Q000737:chemistry*; D006868:Hydrolysis; D009682:Magnetic Resonance Spectroscopy; D010084:Oxidation-Reduction; D011392:Proline / Q000737:chemistry; D053719:Tandem Mass Spectrometry
chemical_list: D000577:Amides; D002264:Carboxylic Acids; D003517:Cyclopentanes; D011392:Proline; C081209:isohumulone