Potent aromatic compounds in the crumb of wheat bread (French-type) - influence of pre-ferments and studies on the formation of key odorants during dough processing

The most important odorants in the crumbs of wheat breads (French-type) prepared according to two different dough recipes using pre-fermentation (crumb I: liquid pre-ferment, containing 0.25% yeast and 1.5% yeast in the final dough; crumb II: soft dough pre-ferment containing 15% yeast and 4.6% yeast in the final dough) were evaluated on the basis of aroma extract dilution analyses. In crumb I, exhibiting the more typical flavour, comparatively higher flavour dilution (FD) factors were found especially for 2-phenylethanol (2-PE) and 3-methyl-butanol (3-MB), while in crumb II the FD factors of methional, 1-octen-3-one, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, butanoic acid and 2- and 3-methylbutanoic acid were higher than in crumb I. Quantitative studies (stable isotope dilution assays) of 2-PE and 3-MB formation, in the liquid pre-ferments containing low yeast concentrations (0.25%) revealed that anaerobic conditions and a fermentation temperature of 35 °C favoured the production of both odorants. Model studies, in which either the 3-MB precursors L-leucine and 3-methylbutanal or the 2-PE precursors L-phenylalanine and phenylacetaldehyde had been added to the pre-ferments, indicated that bakers yeast significantly (15-55%) converted these precursors into the respective odorant.