Bread white, aroma

Since in particular the cracker-like crust odor note was lacking in the synthetic mixture, it was concluded that the character impact compound for this odor note occurs in a concentration in the bread too low to be detected by headspace analysis. Later on the basis of its aroma quality and its very low odor threshold of 0.04 ppb (water), Mulders et al. (19) proposed 2-[(methyldithio)methyl] furan (4 in Figure 1) as the compound which should be responsible for the "golden brown" crust aroma of white bread. 

While several reviews on the role of ingredients are available, none of these describe the flavor chemistry of cracker sponge and dough (2, 3, 4, 5). However, some insight into the chemistry of cracker aroma can be obtained from examination of products that have a "cracker-like aroma" such as white bread crust. 

White bread crust Aroma staling Loss of 2-acetyl-1-pyrroline [32]... 

Grosch, W. (1997) Flavour of white bread. In Kruse, H.-P., Rothe, M. (eds.) Proceedings of the 5th Wartburg Aroma Symposium, University Potsdam, pp. 179-191... 

Mulders E.J., Kleipool R. and ten Noever de Brauw M.C. (1976) 2-((Methyldithio)methyl) furan a characteristic aroma compound of white bread. Chem. lnd. (London), 613-14. 

Constit. of aroma compounds of white bread. Cryst. Mp 48°. Bp 319-320°, Bpno 246°. 

Fig. 5.4. Headspace analysis of aroma substances of white-bread crust, a Capillary gas chromatogram (the arrows mark the positions of the odorants), b FD chromatogram. Odorants 1 methylpropanal, 2 diacetyl, 3 3-methylbutanal, 4 2,3-pentanedione, 5 butyric acid, 6 2-acetyl-1-pyrroline, 7 l-octen-3-one, 8 2-ethyl-3,5-dimethylpyrazine, 9 (E)-2-nonenal (according to Schieberle and Grosch, 1992)...

This characteristic feature appears to be required for a roasted odor. In fact, aU the pyrroUnes and pyridines listed in Table 5.23 as weU as 2-acetyl-thiazole, 2-acetylthiazoline (cf. Table 5.22) and acetylpyrazine (cf. Table 5.23) contain this structural element and have a roasted or cracker-hke odor. However, the thresholds of these compounds vary greatly. The lowest values were found for 2-acetyl-and 2-propionyl-l-pyrrohne. The length of the alkanoyl group also influences the aroma activity because in the transition from 2-propionyl- to 2-hutanoyl-l-pynoline, the roasted note suddenly disappears and the odor threshold increases hy several powers of ten. 2-Acetyl-l-pyrrohne (Apy) is responsible for the typical aroma of the cmst of white bread and it... 

Others. For example, the odour of 2,5-dimethylpyrazine resembles roasted hazelnuts, and 2,6-dimethylpyrazine and trimethylpyrazine have a chocolate-like odour. Important components of coffee aroma include a number of pyrazines, such as 2,3-diethyl-3-methylpyrazine, 2-ethyl-3,5-dimethylpyrazine, 2,6-dimethyl-3-vinylpyrazine and 2-ethyl-6-methyl-3-vinylpyrazine. The flavour-active components of popcorn and white bread are acetylpyrazine, 2-ethyl-3-methylpyrazine, 3-ethyl-2,5-dimethylpyrazine and 5-methyl-6,7-dihydro-5H-cyclopenta[fo] pyrazine. Cyclopentapyrazines, specihcaUy 6,7-dihydro-5H-cyclopenta[fo]pyrazines, are formed in reactions of cyclopen-tenolones with aminoketones and ammonia. 

As mentioned in Section II, chromatograms obtained by FID detection and olfactory response are different. Aroma-active compounds usually do not correspond to the major volatile components in the food. As shown in Fig. 9, many important odorants of white bread crust were not visible in the gas chromatogram, for example, 2-acetyl-1-pyrroline (no. 11) (20). This can be explained by the low odor threshold of these compounds. Identification of such minor components (Fig. 10) is a challenging task. 

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