Bread aroma analysis

The techniques used for the separation of volatiles have been further improved. HPLC and high resolution gas chromatography (HRGC), the latter in combination with effluent sniffing, have been introduced into aroma analysis of bread (25). 

C. Botre, D. Gharpure, Analysis of volatile bread aroma for evaluation of bread freshness using an electronic nose (e-nose). Mater. Manufact. Process. 21, 279-283 (2006)... 

Sampling and Analysis. A frozen slice of bread was cut in pieces and stacked in an enlarged sample flask of an aroma isolation apparatus according to MacLeod and Ames (74). Volatile compounds were trapped on Tenax TA and afterwards thermally desorbed and cold trap injected in a Carlo Erba GC 6000 vega equipped with a Supelcowax 10 capillary column (60 m x 0.25 mm i.d.) and a flame ionisation detector. Similar GC conditions were used for GC-MS identification of volatile compounds by dr. M.A. Posthumus (Dept. Organic Chemistry, VG MM7070F mass spectrometer at 70 eV El, 75). 

Schieberle, P. and Grosch, W. 1987. Quantitative analysis of aroma compounds in wheat and rye bread crusts using stable isotope dilution assay. J. Agric. Food Chem. 35 252-257. 

The composition of the volatile fraction of bread depends on the bread ingredients, the conditions of dough fermentation and the baking process. This fraction contributes significantly to the desirable flavors of the crust and the crumb. For this reason, the volatile fraction of different bread types has been studied by several authors. Within the more than 280 compounds that have been identified in the volatile fraction of wheat bread, only a relative small number are responsible for the different notes in the aroma profiles of the crust and the crumb. These compounds can be considered as character impact compounds. Approaches to find out the relevant aroma compounds in bread flavors using model systems and the odor unit concept are emphasized in this review. A new technique denominated "aroma extract dilution analysis" was developed based on the odor unit concept and GC-effluent sniffing. It allows the assessment of the relative importance of the aroma compounds of an extract. The application of this technique to extracts of the crust of both wheat and rye breads and to the crumb of wheat bread is discussed. 

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. 

The aroma extract dilution analysis of concentrates prepared from the crusts of wheat and rye breads revealed fourty-three odorants in rye and thirty-two in wheat extracts (37). 

The aroma extract dilution analysis was applied to extracts obtained from the crumb of wheat bread. Twenty nine odorants were detected and the flavor compounds responsible for the odor notes identified (Schieberle, P. Grosch, W. in preparation). The 12 aroma compounds having the highest FD-factors are presented in Table IV. 

Table IV. Important Odorants (FD 32) of Wheat Bread Crumb Results of an Aroma Extract Dilution Analysis and Identification Experiments (Schieberle, P Grosch, W. in preparation)...

Crust volatiles were isolated immediately after baking by extraction with dichloromethane and sublimation in vacuo ( ). Application of aroma extract dilution analysis 6) to the acid-free crust extract led to the detection of 31 odorants. After separation and enrichment, these compounds were identified by comparison of the MS/EI, MS/Cl and retention data on two columns of different polarity to reference compounds. Aroma quality was also assessed. The results of the identification experiments (Table I) revealed that 2(E)-none-nal (No. 1), followed by 2(E),4(E)-decadienal (No. 2) and 3-methyl-butanal (No. 3) showed the highest FD-factors in the crust of the chemically leavened bread. Additionally l-octen-3-one, 2(Z)-nonenal, 2(E),4(E)-nonadienal and an unknown compound with a metallic odor contributed high FD-factors to the overall flavor (For a discussion of FD-factors, see Chapter by Schieberle and Grosch, this book). 

Many aroma compounds have been identified in crackers but which ones are the most important has still not been established. Further studies of these extracts should involve the use of odor assays to sort out to aroma important compounds in crackers from the unimportant aroma compounds present. For example, the method used by Shieberle Grosch (33) to describe the odor-active components in bread in terms of their flavor dilution values and the technique called charm analysis (43, 44) both concentrate chemical investigations at retention indices with odor activity. 

Schieberle, R, and Grosch, W. (1987). Evaluation of the flavour of wheat and rey bread crusts by aroma extract dilution analysis. Z. Lebensm. Unters. Forsch., 185, 111-113. 

Although more than 280 compounds have been identified in the volatile fiction of wheat bread, only a small number is responsible for the flavor notes in the crust and the crumb. Schieberle and Grosch (73) used aroma extract dilution analysis (AEDA) to select 32 odorants in wheat. Among the odorants, 2-acetyl-pyrroline (roasly, bread crust-like) was the most potent aroma, followed by E-2-nonenal (green, tallowy), 3-methylbutanal (malty, nutty), diacetyl (buttery) and Z-2-nonenal (green, fiitty). 

A hundred thousand years ago, Man had begun to prepare food with the aid of fire, and started chemistry while cooking. With help from the Maillard reaction, the taste of his food became more sophisticated and pleasant. The typical smell of warm, crusty bread, the marvellous taste of a roast, the fine odour of roasted coffee, the spicy aroma and the colour of beer, result all from this little-known named reaction. Precise analysis of food ingredients and the development of highly specialised processing technologies allow for the industrial-scale preparation of tasty, appealing and readily available meals and snacks, which are... 

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)...

F. Ullrich and W. Grosch, Identification of the most intense odor compounds formed during autoxidation of linoleic acid, Z. Lebensm. Unters. Forsch. 184 277 (1987). W. Grosch and P. Schieberle, Bread flavour qualitative and quantitative analysis, Characterization, production and application of food flavours, Proceedings of 2nd Wartburg Aroma Symp., Akademie-Verlag, Berlin, 1987, p. 139. 

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