AMINO-ACID-METABOLISM BY YEASTS AND LACTIC-ACID BACTERIA DURING BREAD DOUGH FERMENTATION

Metabolism of 22 free amino acids (AA) during fermentation (early and later steps) of wheat dough samples started with pure and associated cultures of yeast and lactic acid bacteria, and commercial compressed yeast (CY) were investigated. Unfermented and fermented straight doughs were studied by Reversed-Phase HPLC of their dansyl derivatives. Used as starters were strains of Saccharomyces cervisiae, Lactobacillus brevis, Lactobacillus plantarum and Enterococcus faecium. Statistical data analysis indicated clustering of samples with yeast and samples without yeast (including uninoculated doughs) respectively, based on rate of metabolism of acidic, basic, aliphatic and aromatic AA. Differences in AA metabolism during the later fermentation step (DF2) categorized bacterial starters into groups according to balance between degree of assimilation (DF2 < 0) and exoproteolytic release (DF2 > 0) of amino acids.