Reference Number: 135
The addition of sour dough during the pro- duction of wheat bread is optional; however the resulting low pH value may be necessary for optimal swelling and baking, control of enzymatic activities, elasticity and suitability for slicing of the crumb, and shelf life. In addition to these technical properties, the metabolic activities of sour dough lactic acid bacteria (LAB) and yeasts are involved in the development of the characteristic bread aroma. Lactobacillus brevis subsp, lindneri CB1, Lactobacillus plantarum DC400 and Saccharo- myces cerevisiae 141 or Saccharomyces exiguus M14 were used as starters to produce wheat sour dough breads. Sour doughs with higher relative percentage of yeast fermentation products (l-propanol, 2-methyl-1-propanol, 3-methyl-1-butanol and ethanol) and with higher total peak area of volatile compounds, or with a more complete profile (higher amounts of ethylacetate and lactic and acetic acids, and the presence of carbonyl compounds) were produced by the associations between lactic acid bacteria (LAB) and S. cerevisiae or S. exiguus M14, respectively. Low temperature (25°C) and sour dough firmness (dough yield 135) were appropriate for LAB souring activities but limited yeast metabolism. Raising the temperature to 30 °C and semi-fluid sour doughs gave more com- plete volatile profiles. Flour ash content from 0.55-1% positively influenced the total amount of volatiles and lactic and acetic acid productions. While at 3 h the sourdough was mainly characterized by iso-alcohols, an increase of leavening time up to 9 h gave a total amount of volatiles about three times higher than that at 5 h and strengthened the LAB con- tribution. The additions of fructose and citrate to the dough enhanced the acetic acid and volatile synthesis by LAB, respectively. After baking, the ethanol disappeared, 2-methyl-l- propanal was synthetized, lactic and acetic acids remained constant, the total amount of volatiles was reduced to a level <12.5% of the initial and an increase in the relative percent- age of iso-alcohols and aldehydes was detected. The differences attributed to the two mixed starters were maintained after baking. A comparison between amino acid and vol- atile profiles before and after baking showed the influence of amino acids on the formation of volatiles during baking
SIGNIFICANCE OF THIS STUDY
The current paper shows that volatile compounds and lactic and acetic acids can be monitored by several biotechnological parameters during wheat sour dough bread productions. Two mixed starters, selec- ted from LAB and yeast cultures isolated from sour doughs, were/ used to produce wheat sour dough breads with different aromatic characteristics. In particular, the species of yeast (S. cerevisiae 141 or S. exiguus M14) associated with LAB were fundamental in determining different volatile profiles. Temperature, dough yield, time of leavening and type of flour were demonstrated to variously affect volatile and organic acid productions. Additions of fructose or citrate to the dough represented a tool for increasing LAB contribution on sensory quality, and influenced the dynamics of volatile formation during baking. Amino acid concentrations and profiles of sour doughs, in particular Valine, Leucine and Lysine, had some influences on volatile synthesis during baking.