Several thousand years ago, dough was already being fermented to produce loaves and similar bakery products with a porous crumb, a significant step forward in baking methods (1,2). This method of baking was based on gas formation caused by fermentation, which produced doughs with a frothy consistency. Figure 1 shows that fermentation is the key process for bread production. As pointed out in Table 1, the leavening of dough by gas formation is accompanied by microbial and biochemical conversion of dough constituents, which results from the action of microorganisms added to the dough and/or which proliferate in the dough and enzymes present in the flour. These conversions require specific conditions from which the working parameters and the technical realization of the fermentation processes result.

Gas formation is the most important effect of fermentation because it creates the foamlike structure of dough that is the prerequisite for a rapid heat flow through the doughs. Heat applied to doughs permits the gas and water vapor to be expelled from the dough while gelatinization of the starch causes the frothy structure of the dough to set, thus producing the crumb. Before dough was leavened by fermentation, it was only possible to bake flat pieces of dough. The thinness of the dough allowed heat to be transferred so rapidly that a loose, coarse dough structure resulted because of water evaporation.

Dough fermentation is based on metabolic activities of yeast and lactic acid bacteria. The ability of these microorganisms to anaerobically produce functional metabolites in doughs, made from flours of wheat and rye milling products varying in composition, is used to achieve the effects shown in Table 2. These primary, secondary, and tertiary effects have been classified according to kinds and functions in bread baking. The individual effects and their interdependence in bakery products have already been comprehensively described (36). By controlling the processing parameters of microbiological fermentations and those of technical methods of dough preparation, it is possible to affect microorganisms and enzyme activities present in the dough as required for the particular dough characteristics, such as volume, consistency, and metabolite formation.

The action of yeast, lactic acid bacteria, and enzymes present in doughs can be assisted by adding enzyme preparations (malt flour, a-amylases, pentosanases) and other ingredients (sugar, emulsifiers, ascorbic acid) to the recipes. It should also be mentioned that besides assisting the microbial and enzymic action by recipe modulation, it is also possible to

Figure 1 Simplified diagram for bread production from fermented doughs.

improve the performance of the microorganisms by genetic modification (7-9). The dough-making performance of flours can also be improved by genetically modifying the viscoelastic properties of wheat varieties (10,11).

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