B-damascenone

In an alcohol-free beer, the concentrations of the beer odorants were 5 to 10-fold lower than in the pale lager beer [18] suggesting that the former beer is a very appropriate matrix for the determination of odor thresholds. A determination of the odor thresholds in the alcohol-free beer revealed (Table 15) that, compared to water, the odor threshold of all odorants increased, but to a different extent. For instance, the threshold of (E)-B-damascenone increased by a factor of 2500, while that of HDF was enhanced only by a factor of eight. Odor activity values calculated on the basis of the odor thresholds in the alcohol-free beer (Table 15) now confirmed the significant contribution of HDF to the dark beer flavor. 

In the following, strategies to localize precursors of key odorants on the basis of systematic quantitative studies on food fractions and model systems will be illustrated for the important odorants 4-hydroxy-2,5-dimethyI-3(2H)-furanone and (E)-B-damascenone. 

The precursor structures can be elucidated by HRGC/MS and HRGC/FTTR of the acetylated derivatives or aglycons, respectively. Very recently, direct LC/MS measurement of a non-derivatized precursor glycoside of (E)-B-damascenone isolated from apples has been reported [100]. Application of such techniques on precursor fractions from wine [97, 101]... 

Isolation of Two Glucosidic Precursors of B-Damascenone From Riesling Wine. 

Figure 7. Structures of two acetylenic precursors of B-damascenone 19 isolated from Riesling wine.

The skillful assistance of M. Messerer is gratefully acknowledged. Dr. G. Skouroumounis is thanked for his helpful comments on the B-damascenone studies. The Deutsche Forschungsgemeinschaft, Bonn, is thanked for fundmg the research. 

Comparing the odor spectrum gas chromatograms of the three wines, in Figure 3, a general effect was observed. Floral, fruity compounds were the dominant odorants in the "no Brett" wine while rancid, plastic odors accounted for 1/3 or less of the odor activity in the "medium Brett" wine, the floral, fhiity compounds decrease to 1/2 or less of the odor activity while the rancid, plastic compounds increase to 2/3 in the "high Brett" wine, the rancid, plastic compounds were the dominant odorants while the floral, fhiity compounds were far less dominant. The floral odorant identified as 2-phenyl ethanol was the dominant compound in "no Brett" and "medium Brett" wines in the "high Brett" wine, it was equally as dominant as isovaleric acid and the unknown compound. The fiuity odorant B-damascenone was equally dominant among the three wines for this reason, it should not be considered as a contributor to "Brett" aroma. 

Brett flavor in wine The question still remains what is "Brett" flavor Results from our initial work indicates that "Brett" aroma in wine is a complex mixture of odor-active compounds, including acids, alcohols, aldehydes, ketones, esters, and phenolics. Analysis by gas chromatography-olfactometry revealed two predominate odor-active compounds responsible for the Brett flavor in the wines studied isovaleric acid and a second unknown compound other identified odor-active compounds included 2-phenyl ethanol, isoamyl alcohol, cis-2-nonenal, trans-2-nonenal, B-damascenone, ethyl decanoate, guaiacol, 4-ethyl guaiacol, 4-ethyl phenol. Our findings are a snapshot into the much larger picture know as Brett flavor. Ultimately this preliminary investigation requires the descriptive analyses of many more wines to know what odor active compounds describe the flavor know as "Brett". 

Figure 4. Polyamide, PVP, and secondary C18 chromatographic separations of B-damascenone precursor from extracts of Concord grapes.

Fig. 6 Structures of glycosidically-bound aroma precursors of B-damascenone 7, theaspiranes 8, theaspirones 9, vitispiranes 10, and edulans 11, i.e. 3-hydroxy-7,8-didehydro-B-ionol 15, 4-hy

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