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, 73 (15), 4741-50

Population Dynamics and Metabolite Target Analysis of Lactic Acid Bacteria During Laboratory Fermentations of Wheat and Spelt Sourdoughs

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Population Dynamics and Metabolite Target Analysis of Lactic Acid Bacteria During Laboratory Fermentations of Wheat and Spelt Sourdoughs

Roel Van der Meulen et al. Appl Environ Microbiol.

Abstract

Four laboratory sourdough fermentations, initiated with wheat or spelt flour and without the addition of a starter culture, were prepared over a period of 10 days with daily back-slopping. Samples taken at all refreshment steps were used for determination of the present microbiota. Furthermore, an extensive metabolite target analysis of more than 100 different compounds was performed through a combination of various chromatographic methods including liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry. The establishment of a stable microbial ecosystem occurred through a three-phase evolution within a week, as revealed by both microbiological and metabolite analyses. Strains of Lactobacillus plantarum, Lactobacillus fermentum, Lactobacillus rossiae, Lactobacillus brevis, and Lactobacillus paraplantarum were dominating some of the sourdough ecosystems. Although the heterofermentative L. fermentum was dominating one of the wheat sourdoughs, all other sourdoughs were dominated by a combination of obligate and facultative heterofermentative taxa. Strains of homofermentative species were not retrieved in the stable sourdough ecosystems. Concentrations of sugar and amino acid metabolites hardly changed during the last days of fermentation. Besides lactic acid, ethanol, and mannitol, the production of succinic acid, erythritol, and various amino acid metabolites, such as phenyllactic acid, hydroxyphenyllactic acid, and indolelactic acid, was shown during fermentation. Physiologically, they contributed to the equilibration of the redox balance. The biphasic approach of the present study allowed us to map some of the interactions taking place during sourdough fermentation and helped us to understand the fine-tuned metabolism of lactic acid bacteria, which allows them to dominate a food ecosystem.

Figures

FIG. 1.
FIG. 1.
Population dynamics of LAB (gray bars) and yeast (white bars) counts during a 10-day spelt sourdough fermentation with daily back-slopping. Counts were performed in triplicate, and mean values ± standard deviations are represented.
FIG. 2.
FIG. 2.
Changes in pH during a 10-day spelt sourdough fermentation with daily back-slopping. Symbols: •, changes in pH during the first day of fermentation (0 to 24 h); ▪, changes in pH during the second day of fermentation (24 to 48 h); ▴, changes in pH during the last day of fermentation (216 to 240 h).
FIG. 3.
FIG. 3.
Bacterial population dynamics shown by 16S rRNA PCR-DGGE analysis of two spelt (top) and two wheat (bottom) sourdough fermentations, daily back-slopped, with flour from two different mills (A and B), after each day (0, 24, 48, 72, 96, 120, 144, 168, 192, 216, and 240 h). M, reference marker. The indicated bands (arrows) correspond with cereal DNA.
FIG. 4.
FIG. 4.
Results of the additional 16S rRNA PCR-DGGE run, including the normalized PCR-DGGE profiles of stable sourdoughs after 10 days of back-slopping followed by the PCR-DGGE profiles of strains isolated and purified from the corresponding sourdoughs. Lane 1, profile of the dominant population in the spelt A sourdough; lanes 2 and 3, profiles of purified cultures isolated from the stable spelt A sourdough; lane 4, profile of the dominant population in the spelt B sourdough; lanes 5 to 7, profiles of purified cultures isolated from the stable spelt B sourdough; lane 8, profile of the dominant population in the wheat A sourdough; lane 9, profile of the purified culture isolated from the stable wheat A sourdough; lane 10, profile of the dominant population in the wheat B sourdough; lanes 11 and 12, profiles of purified cultures isolated from the stable wheat B sourdough; lane 13, profile of mitochondrial cereal DNA.
FIG. 5.
FIG. 5.
Evolution of the maltose concentration during a 10-day daily back-slopped sourdough fermentation with spelt A (black bars), wheat A (light gray bars), spelt B (white bars), and wheat B (dark gray bars).
FIG. 6.
FIG. 6.
Evolution of total amino acid concentration (top) and ornithine concentration (bottom) during a 10-day daily back-slopped sourdough fermentation with spelt A (black bars), wheat A (light gray bars), spelt B (white bars), or wheat B (dark gray bars).
FIG. 7.
FIG. 7.
Evolution of ethanol concentration (white bars, left axis) and yeast counts (solid line, right axis) during the 10-day daily back-slopped spelt B sourdough fermentation.
FIG. 8.
FIG. 8.
Changes in the production of 3-methyl-1-butanol (black bars), 2-methyl-1-propanol (light gray bars), 1-propanol (white bars), and 3-methyl-1-butanol acetate (dark gray bars) during the 10-day daily back-slopped spelt A sourdough fermentation. AU, arbitrary units [100 × peak area compound (peak area internal standard × g sample)−1].

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