Flavor precursors bread flavors

Shortened fermentation or baking steps during bread making often result in bread of poor flavor quality. To improve the flavor of bread produced by modern technology it is necessary to gain information about precursors and reaction routes leading to important bread flavor compounds. 

Bread flavor. White bread During the baking process the impact substances 2-acetyl-1 -pyrroline and 2-ace-tyl-A (A )-tetrahydropyridine form in the crust, on storage their concentrations decrease rapidly. Precursors are metabolites of yeasL Also of importance are ( )-2-nonenal (see alkenals), 3-methylbutanal (see al-kanals), 2,3-butanedione, and methional. In bread crumbs, degradation products of linolic acid such as ( )- and (Z)-2-nonenaJ and ( , )- 2,4-decadienal predominate. 

The thermal generation of flavor is a very essential process for the "taste" of many different foodstuffs, e.g. cocoa, coffee, bread, meat. The resulting aromas are formed through non-enzymatic reactions mainly with carbohydrates, lipids, amino acids (proteins), and vitamins under the influence of heat. Thiamin (vitamin B ) and the amino acids, cysteine and methionine, belong to those food constituents which act as flavor precursors in thermal reactions. The role of thiamin as a potent flavor precursor is related to its chemical structure which consists of a thiazole as well as a pyrimidine moiety. The thermal degradation of this heterocyclic constituent leads to very reactive intermediates which are able to react directly to highly odoriferous flavor compounds or with degradation products of amino acids or carbohydrates. 

The organic acids generated by fermenting bacteria such as acetic, lactic, hydroxya-cetic, formic, pyruvic, etc., are the main flavor precursors. Acetic add is considered the main acid. It improves dough characteristics, speeds up fermentation, and affects final bread properties. It is generated mainly from maltose and other simpler carbohydrates. 

Second, the essential amino acids leucine, isoleucine, and phenylalanine are precursors for several additional tomato flavor elements. Here, too, these flavor elements are important flavor constituents in other fruits, including strawberries and apples. They are also found in breads, cheeses, wine, and beer. 

The caramel-like smelling HDF has been established as a main contributor to the flavors of several processed foods (Table 17). In addition, it should be noted that in all these foods, on the basis of a high FD-factor, HDF was also by far the most important caramel-like smelling odorant. In the following, the strategy in the HDF precursor analysis will be shown using wheat bread crust, popcorn [88] and malt as the examples. Quantitative measurements were performed by using a stable isotope dilution assay (cf. Section 3.2.). 

The flavor compounds of the crust from the chemically leavened model bread were then compared to those recently identified (6) in the crust of a standard wheat bread which was leavened by addition of yeast (Table I). One striking difference was that Acp (No. 16), which showed the highest FD-factor in the yeast-leavened bread showed a very low FD-factor in the chemically leavened bread. This indicated, that the flour contained only minor amounts of the precursor (s) for the formation of Acp. On the other hand, 2(E),4(E)-decadienal, 2(E),4(E)-nonadienal, l-octen-3-one and 2(Z)-nonenal, which are undoubtedly formed by a heat-induced oxidative degradation of the flour lipids, became predominant odorants in the chemically leavened compared to the yeast-leavened bread. 

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