Identification and RP-HPLC-ESI-MS/MS quantitation of bitter-tasting beta-acid transformation products in beer.
Thermal treatment of the hop beta-acid colupulone under wort boiling conditions, followed by LC-TOF-MS and 1D/2D NMR spectroscopy, revealed cohulupone, hulupinic acid, nortricyclocolupone, two tricyclocolupone epimers, two dehydrotricyclocolupone epimers, two hydroxytricyclocolupone epimers, and two hydroperoxytricyclocolupone epimers as the major bitter-tasting beta-acid transformation products. Among these compounds, the chemical structures of the hydroxy- as well as the hydroperoxytricyclocolupone epimers have not previously been confirmed by 1D/2D NMR experiments. Depending on their chemical structure, these compounds showed rather low recognition thresholds ranging from 7.9 to 90.3 micromol/L. The lowest thresholds of 7.9 and 14.7 micromol/L were found for cohulupone, imparting a short-lasting, iso-alpha-acid-like bitter impression, and for hydroxytricyclocolupone, exhibiting a long-lasting, lingering, and harsh bitterness perceived on the posterior tongue and throat. Furthermore, HPLC-ESI-MS/MS analysis allowed for the first time a simultaneous detection and quantitation of these bitter-tasting beta-acid transformation products in a range of commercial beer samples without any sample cleanup. Depending on the type of beer, these studies revealed remarkable differences in the concentrations of the individual beta-acid transformation products.
Haseleu
Gesa
G
Food Chemistry and Molecular Sensory Science, Technische Universitat Munchen, Lise-Meitner Strasse 34, Freising, Germany.
Intelmann
Daniel
D
Hofmann
Thomas
T
D000143:Acids / Q000737:chemistry*; D000328:Adult; D001515:Beer / Q000032:analysis*; D002851:Chromatography, High Pressure Liquid; D056148:Chromatography, Reverse-Phase; D005260:Female; D006801:Humans; D027582:Humulus / Q000737:chemistry*; D008297:Male; D015394:Molecular Structure; D013237:Stereoisomerism; D053719:Tandem Mass Spectrometry; D013649:Taste; D055815:Young Adult
D000143:Acids