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

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.Sourdough is a mixture of ground cereals (e.g., wheat or rye) and water that is spontaneously fermented. Sourdough fermentations improve dough properties, enhance both bread texture and bread flavor, and delay bread spoilage (28). Lactic acid bacteria (LAB) and yeasts play a key role in sourdough fermentation processes (9,21,26,28,29,55). Sourdough LAB have been intensively studied with respect to their carbohydrate metabolism (16,24,60), proteolysis and amino acid metabolism (16,23,58,69), lipid metabolism (16), and production of volatile compounds (7,31,32). Besides these general metabolic traits, specific metabolic properties have been recognized in sourdough LAB, such as the use of alternative electron acceptors (59, 61), the production of antifungal compounds (38,45,57), the biosynthesis of exopolysaccharides (36, 63, 64), and arginine catabolism (8, 53). These metabolic traits of sourdough LAB highlight their adaptation to the sourdough environment. For instance, fructose-to-mannitol and arginineto-ornithine conversion favor ATP generation and/or acid stress (16). Also, interactions between sourdough LAB and yeasts have been studied in detail (9, 21).The microbial growth and activity of LAB in so...

Probiotic properties of lactic acid bacteria isolated from traditionally fermented Xinjiang cheese

“…All strains from this study were able to tolerate pH 3.0 with a survival percentage of more than 70%, and therefore they can be considered as acidtolerant LAB strains. This tolerance capacity of lactic acid bacteria warranted the production of various antimicrobial substances which might create unfavorable conditions for the growth of pathogens as well as toxigenic and spoilage organisms in humans and/or animals (van der Meulen et al, 2007).…”

Diversity and dynamics of bacterial populations during spontaneous sorghum fermentations used to produce ting, a South African food

“…Culture-dependent approaches represent the only means of recovering microorganisms from the fermented substrate [50], although it is widely recognized that they do not allow analysis of true diversity and/or population dynamics [3,49,58]. On the other hand, various studies have shown that culture-independent approaches, such as denaturing gradient gel electrophoresis of 16S rRNA gene amplicons (PCR-DGGE), provide a more reliable and reproducible means for studying microbial populations in complex food ecosystems [9,16,65,75].…”

“…PCR was performed as described previously [75] on a MyCycler TM thermal cycler (BioRad, Hercules, USA). The 16S rRNA V3 region was also amplified from 13 different bacterial reference strains, and the resulting amplicons were combined for use as a DGGE reference standard [75].…”

“…PCR was performed as described previously [75] on a MyCycler TM thermal cycler (BioRad, Hercules, USA). The 16S rRNA V3 region was also amplified from 13 different bacterial reference strains, and the resulting amplicons were combined for use as a DGGE reference standard [75]. The reference standard comprised amplicons from Bacteroides fragilis (DSM 1396), Bacteroides thetaiotaomicron (LMG 11262), Weissella cibaria (LMG 17699), Enterococcus flavescens (LMG 13518T), E. solitarius (LMG 12890T), Leuconostoc fructosum (LMG 9498T), Bacillus subtilis (LMG 7135T), Clostridium butyricum (LMG 1212), Lb.…”

“…lactis (LMG 18314T), and Bifidobacterium dentium (LMG 11045T). DGGE was performed according to the procedure described by Muyzer et al [55] with slight modifications, as described previously [75]. All PCR-DGGE experiments were performed in duplicate.…”