Bread toasting, aroma

Additional odorous components, such as 3-ethyl-2,5-dimethylpyrazine, biacetyl, 3-methylbutanal, 2-phenylethanal and others are found in dark rye bread. Toasted bread contains the same compounds that carry the aroma of bread crust and crumb. A key component is again 2-acetyl-l-pyrroHne, other major components are methional, 4-hydroxy-2,5-dimethyl-2H-furan-3-one (furaneol), ( )-non-2-enal and biacetyl, the odour of which resembles butter. 

Many bland, or even downright unpleasant-tasting, substances are transformed into some of the most desirable flavors and popular foods by roasting. Thus, those foods, representing such different tastes and aromas as chocolate, bread, roast beef, coffee, and toasted nuts have in common the fact that they are products of the Maillard browning... 

The concentrations of furfurylsulfides and -disulfides wich possess toasted, bread- and meat-like aromas do not change during storage of roasted coffee. Sulfur containing furans are formed by heating furanaldehydes with cysteine and methionine, respectively (24). 

Pyrazines. In the thirties, the attention on pyrazines was focused on its industrial role in dyes, photographic emulsions and chemotherapy. Its importance in life processes was indicated in its derivative, vitamin B2 (riboflavin, 6,7-dimethyl-9-(l -D-ribityl isoalloxazine). Later,in the midsixties, it was identified in foods and its contributions to the unique flavor and aroma of raw and processed foods attracted the attention of flavor chemists Pyrazine derivatives contribute to the roasting, toasting, nutty, chocolaty, coffee, earthy, caramel, maple-like, bread-like, and bell pepper notes in foods. The reader is referred to the reviews on Krems and Spoerri (88) on the chemistry of pyrazines, and the review of pyrazines in foods by Maga and Sizer (89, 90) Table XVI summaries sensory description and threshold of selected pyrazines. 

The Amadori products decompose to characteristic a-dicarbonyl compounds and 5-hydroxymethylfurfural (bread and coffee aroma). In the end, like their aldimines or ketimines, they lead in foUow-on reactions to melanoidins (high molecular-weight compounds), which, together with caramel products, create the brown colour of grilled or toasted food. 

An alternative source of characteristic heated flavor compounds is via the Maillard pathway, the thermally induced reaction between amino acids and reducing sugars. Aroma constituents in chocolate, coffee, toasted bread, and popcorn are products of Maillard reactions, in addition to flavors in roasted nuts and meats, which are discussed in Sec. II.E and 11.E. Guaiacols occur as pyrolysis products of carbohydrates or lipids in smoked or char-broiled meats. 

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