M. A. Martínez-Anaya

Headspace flavour compounds produced by yeasts and lactobacilli during fermentation of preferments and bread doughs.

Production of volatile flavour compounds during fermentation with pure cultures of Saccharomyces cerevisiae and Candida guilliermondii, Lactobacillus brevis and Lactobacillus plantarum have been investigated, using wheat doughs and several preferements as substrates. For yeast, preferments consisted of 10% (w/v) glucose, maltose and sucrose solutions, whereas for lactobacilli they consisted of supplemented and unsupplemented (3% and 10% (w/v)) glucose solutions, and a 10% (w/v) wheat flour slurry. Seven volatile compounds (acetaldehyde, acetone, ethyl acetate, ethanol, hexanal+isobutyl alcohol, and propanol) were detected when using yeasts. All these compounds, except propanol, appeared for all the substrates assayed, with ethanol as the predominant component. Generally, S. cerevisiae produced higher amounts of the different components than C. guilliermondii. Both yeasts produced larger amounts of volatile flavour compounds during fermentation in glucose and sucrose solutions than in maltose or wheat dough. In general the yeasts examined produced more flavour components than the lactobacilli. For the lactobacilli the highest number of volatile flavour compounds were observed for substrates containing flour.

Sugar uptake and involved enzymatic activities by yeasts and lactic acid bacteria: their relationship with breadmaking quality

The uptake kinetics of sugars present in wheat doughs and alpha-glucosidase as well as beta-fructosidase activities were determined in different strains of yeasts and lactic acid bacteria. These strains were previously selected according to their breadmaking quality. Saccharomyces cerevisiae (P6), Candida guilliermondii (P40), Lactobacillus plantarum (B31 and La18) and L. brevis (B21) showed good performance, while Sacch. fructuum (P43), L. cellobiosus (B37) and Enterococcus faecium (B11) yielded bread of lower quality. Leuconostoc mesenteroides (B10), when used in combination with other strains led also to high quality starters. All yeast strains used assimilated glucose, fructose and maltose, exhibiting saturable kinetics. Lactic acid bacteria showed saturable kinetics only for hexoses, whereas disaccharide uptake was linear. Sacch. cerevisiae, Leuconostoc mesenteroides, L. brevis and L. plantarum (B31) displayed better sugar uptake properties. For all the strains used alpha-glucosidase and beta-fructosidase activities were detected. The highest specific activities were found for Sacch. cerevisiae, C. guilliermondii and L. plantarum (B31). These results indicate good correlation between the parameters evaluated and the breadmaking potential of the microorganisms.

Effect of processing conditions on acidification properties of wheat sour doughs.

The pH, total titratable acidity (TTA) and lactic and acetic acids production have been investigated for wheat sour doughs with and without yeast addition, inoculated with two strains of Lactobacillus plantarum (B33, B39). To study the effect of flour extraction rate (0.54, 11.11 and 1.68% ash content), dough yield (DY) (160, 200 and 240 of sour dough/100 g flour), and fermentation temperature (25, 30 and 35 degrees C) a response surface regression, factor analysis and K-means clustering analysis were used. Results from factor analysis point out that the extraction rate of fluor governs TTA and acetic acid content; this factor accounts for the 53% of variability of the data. Dough yield is highly correlated with lactic acid content, explaining 27% of the total variance. Finally, temperature explains the remaining 16% of variation, but it is not related to any analytical variable. From K-means clustering analysis, flour extraction rate of 1.68% ash content leads to the highest TTA and acetic acid values, whereas DY of 240 g sour dough/100 g flour gives the greatest lactic acid content, and DY of 160 leads to the lowest levels of TTA and organic acids.