Cereal Chem 47:247 - 258.  |  VIEW ARTICLE
Influence of Yeast Fermentation and Baking on the Content of Free Amino Acids and Primary Amino Groups and Their Effect on Bread Aroma Stimuli.

A. A. El-Dash and J. A. Johnson. Copyright 1970 by the American Association of Cereal Chemists, Inc. 

Yeast is a potential source of primary amino groups in dough. When yeast was added to dough, approximately a 400% increase in total free amino acids was observed. Lysine, alanine, proline, cystine, and dicarboxylic acids showed the highest percentage increase of all amino acids analyzed. Although fermentation reduced the dough content of free amino acids, about twice as much remained in the dough after fermentation as was originally present in flour. The marked decrease in free amino acid content in the bread crust demonstrated their importance in the nonenzymatic browning reaction during baking. Amino acids in the crust were reduced for all free amino acids except the aromatics. Basic and sulfur-containing amino acids, proline, and glutamic acid were the most reactive in browning. The concentration of intermediate compounds and brown melanoidin pigments produced by the nonenzymatic browning reaction was considerably increased in bread crust as a result of fermentation which improved bread flavor. The fermentation process had no effect on the type of carbonyl compounds produced in bread crust, but changed the quantity of carbonyl compounds. Furfural and 5-(hydroxymethyl)-2-furaldehyde (hydroxymethylfurfural), 2-propanone, 2-methylpropanal, butanal, 2-methylpentanal, and an unknown carbonyl compound were increased slightly in bread crust by fermentation.