Received for review March 14, 2007. Revised manuscript received May 16, 2007. Accepted May 20, 2007. G.T.E. acknowledges the Tertiary Education Commission, New Zealand, for providing scholarship funding. P.J.M. gratefully acknowledges the ongoing support of Leco Australia.

Abstract:

The "spicy" character of hops is considered to be a desirable attribute in beer, associated with "noble hop aroma". However, the compounds responsible have yet to be adequately identified. Odorants in four samples of the spicy fraction of hop essential oil were characterized using gas chromatography-olfactometry (GC-O) and CharmAnalysis. Four hop varieties were compared, namely, Target, Saaz, Hallertauer Hersbrucker, and Cascade. Odor-active compounds were tentatively identified using comprehensive two-dimensional gas chromatography (GC×GC) combined with time-of-flight mass spectrometry (TOFMS). An intense "woody, cedarwood" odor was determined to be the most potent odorant in three of the four spicy fraction samples. This odor coincided with a complex region where between 8 and 13 compounds were coeluting in each of the four spicy fractions. The peak responsible was determined by (i) correlating peak areas with Charm values in eight hop samples and (ii) heart-cut multidimensional gas chromatography-olfactometry (MDGC-O). The compound responsible was tentatively identified as 14-hydroxy--caryophyllene. Other important odorants identified were geraniol, linalool, -ionone, and eugenol.

Keywords: Humulus lupulus L.; gas chromatography-olfactometry; comprehensive two-dimensional gas chromatography; time-of-flight mass spectrometry; multidimensional gas chromatography; hop aroma; character-impact odorants

Download the full text: PDF | HTML