BIOCHEMICAL EVOLUTION OF NITROGEN-COMPOUNDS DURING FERMENTATION OF WHEAT BREAD DOUGHS CONTAINING PURE CULTURES OF LACTIC-ACID BACTERIA

The metabolic activities of three species of lactic acid bacteria (Lactobacillus brevis, L. plantarum and Streptococcus faecium) during wheat bread dough fermentation have been investigated by evaluating the biochemical changes which occur in 0.85 mol/L NaCl-soluble nitrogen components in unfermented, 4-h and 24-h fermented straight doughs. Non-protein nitrogen compounds increase during a 24-h-fermentation period in all doughs. Exoproteolytic activity is denoted mainly in L. plantarum fermented doughs by an important rise in the free amino acids. Doughs containing L. brevis show a larger production of peptides over a 24-h fermentation period and strong nutritional requirements on low-molecular-weight peptides are evidenced by Streptococcus faecium over short fermentation periods. Progressive depletion in the polypeptides and protein contents as well as a decrease in the estimated protein chain length over the fermentation period for L. plantarum and St. faecium containing doughs are evidence of endoproteolytic activities in the high-molecular-weight soluble components. An increase in the size of the protein fragments released in the 4-h fermented doughs containing L. brevis denotes enzymatic hydrolysis on non-soluble protein chains. © 1990 Springer-Verlag.