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...
The influence of turning and environmental contamination on six spontaneous cocoa bean heap fermentations performed in Ghana was studied through a multiphasic approach, encompassing both microbiological (culture-dependent and culture-independent techniques) and metabolite target analyses. A sensory analysis of chocolate made from the fermented, dried beans was performed as well. Only four clusters were found among the isolates of acetic acid bacteria (AAB) identified: Acetobacter pasteurianus, Acetobacter ghanensis, Acetobacter senegalensis, and a potential new Acetobacter lovaniensis-like species. Two main clusters were identified among the lactic acid bacteria (LAB) isolated, namely, Lactobacillus plantarum and Lactobacillus fermentum. No differences in biodiversity of LAB and AAB were seen for fermentations carried out at the farm and factory sites, indicating the cocoa pod surfaces and not the general environment as the main inoculum for spontaneous cocoa bean heap fermentation. Turning of the heaps enhanced aeration and increased the relative population size of AAB and the production of acetic acid. This in turn gave a more sour taste to chocolate made from these beans. Bitterness was reduced through losses of polyphenols and alkaloids upon fermentation and cocoa bean processing.Raw cocoa beans have an astringent, unpleasant flavor and have to be fermented, dried, and roasted to obtain the desired characteristic cocoa flavor (27,30,41,45). Fermentation is hence the first step in cocoa powder and chocolate production. It is carried out spontaneously in heaps, boxes, baskets, or trays in cocoa-producing countries in the equatorial zone, led by the Ivory Coast, Brazil, and Ghana (1, 27). During the last decade, knowledge about the spontaneous cocoa bean fermentation process has been increasing (2,5,26,33,34,37). The microbiota involved in natural cocoa bean fermentation reflects the environmental factors (temperature, pH, and oxygen tension) and the metabolism of substrates of the cocoa bean pulp. This results in production times of significant amounts of ethanol, lactic acid, and acetic acid, representing a succession of yeasts, lactic acid bacteria (LAB), and acetic acid bacteria (AAB) during the cocoa bean fermentation course (2, 5, 36-38).In the last 5 years, the microbiology and biochemistry of Ghanaian cocoa bean heap fermentation processes have been studied in detail (5,18,26,33,34). During early and mid-time spontaneous fermentation of freshly harvested pulp and cocoa beans, piled into a heap, yeasts produce ethanol under anaerobic conditions and cause depectinization of the pulp, enabling the pulp to flow away and air ingress (37, 38). Concerning microaerophilic LAB, citrate-fermenting, acid-tolerant, and ethanol-tolerant Lactobacillus plantarum and Lactobacillus fermentum strains dominate the spontaneous cocoa bean fermentation process (5, 34). Citrate and sugars are converted into acetic acid, lactic acid, and mannitol, enabling a slight increase of the pH of the pulp (5). During the aerobic phase, ...
A culture-based approach was used to investigate the diversity of lactic acid bacteria (LAB) in Belgian traditional sourdoughs and to assess the influence of flour type, bakery environment, geographical origin, and technological characteristics on the taxonomic composition of these LAB communities. For this purpose, a total of 714 LAB from 21 sourdoughs sampled at 11 artisan bakeries throughout Belgium were subjected to a polyphasic identification approach. The microbial composition of the traditional sourdoughs was characterized by bacteriological culture in combination with genotypic identification methods, including repetitive element sequence-based PCR fingerprinting and phenylalanyl-tRNA synthase (pheS) gene sequence analysis. LAB from Belgian sourdoughs belonged to the genera Lactobacillus, Pediococcus, Leuconostoc, Weissella, and Enterococcus, with the heterofermentative species Lactobacillus paralimentarius, Lactobacillus sanfranciscensis, Lactobacillus plantarum, and Lactobacillus pontis as the most frequently isolated taxa. Statistical analysis of the identification data indicated that the microbial composition of the sourdoughs is mainly affected by the bakery environment rather than the flour type (wheat, rye, spelt, or a mixture of these) used. In conclusion, the polyphasic approach, based on rapid genotypic screening and high-resolution, sequence-dependent identification, proved to be a powerful tool for studying the LAB diversity in traditional fermented foods such as sourdough.Sourdough represents a natural food ecosystem in which the fermentation activities of lactic acid bacteria (LAB) and yeasts largely determine the typical characteristics of the resulting baked goods (26). Based on the production technology, sourdough fermentations can be divided into three types (2, 38): type I, or traditional, sourdoughs are characterized by continuous propagation of the dough at ambient temperatures (20 to 30°C); type II, or industrial, sourdoughs are incubated at high temperatures (Ͼ30°C), with longer fermentation times and a higher water content; and type III sourdoughs are dried preparations of industrial doughs. Traditional Belgian sourdoughs belong to type I sourdoughs. The use of sourdough improves the overall characteristics of bakery products, such as the dough properties, texture, and flavor (16). LAB contribute significantly to these properties, e.g., by acidification of the dough (17), proteolysis of the gluten (10), hydrolysis of the starch (5), and the production of taste and aromatic compounds (15). Moreover, several sourdough LAB inhibit the development of pathogens due to the production of acids and bacteriocins (22). During spontaneous sourdough maturation, LAB occur as the predominant microorganisms, at numbers of Ͼ10 8 CFU/g sourdough. The genera Lactobacillus, Pediococcus, Leuconostoc, and Weissella predominate in this ecosystem, whereas lactococci, enterococci, and streptococci are rarely found. Sourdough LAB may originate from natural contamination of the flour or may be introduced i...
A total of 39 traditional sourdoughs were sampled at 11 bakeries located throughout Belgium which were visited twice with a 1-year interval. The taxonomic structure and stability of the bacterial communities occurring in these traditional sourdoughs were assessed using both culture-dependent and cultureindependent methods. A total of 1,194 potential lactic acid bacterium (LAB) isolates were tentatively grouped and identified by repetitive element sequence-based PCR, followed by sequence-based identification using 16S rRNA and pheS genes from a selection of genotypically unique LAB isolates. In parallel, all samples were analyzed by denaturing gradient gel electrophoresis (DGGE) of V3-16S rRNA gene amplicons. In addition, extensive metabolite target analysis of more than 100 different compounds was performed. Both culturing and DGGE analysis showed that the species Lactobacillus sanfranciscensis, Lactobacillus paralimentarius, Lactobacillus plantarum, and Lactobacillus pontis dominated the LAB population of Belgian type I sourdoughs. In addition, DGGE band sequence analysis demonstrated the presence of Acetobacter sp. and a member of the Erwinia/Enterobacter/Pantoea group in some samples. Overall, the culture-dependent and culture-independent approaches each exhibited intrinsic limitations in assessing bacterial LAB diversity in Belgian sourdoughs. Irrespective of the LAB biodiversity, a large majority of the sugar and amino acid metabolites were detected in all sourdough samples. Principal component-based analysis of biodiversity and metabolic data revealed only little variation among the two samples of the sourdoughs produced at the same bakery. The rare cases of instability observed could generally be linked with variations in technological parameters or differences in detection capacity between culture-dependent and culture-independent approaches. Within a sampling interval of 1 year, this study reinforces previous observations that the bakery environment rather than the type or batch of flour largely determines the development of a stable LAB population in sourdoughs.Traditional sourdoughs comprise a complex microbial association of lactic acid bacteria (LAB) and yeasts and are thought to improve sensory, texture, and health-promoting properties of many bakery products (15). During sourdough fermentation, the prevailing LAB produce acids (mainly lactic acid and acetic acid) that lower the pH of the sourdough medium. In addition, these organisms are responsible for the production of ethanol, aroma compounds, bacteriocins, exopolysaccharides, and several enzymes (17). Sourdough LAB may originate with natural contaminants in the flour or with a starter culture which contains one or more LAB strains (6). Sourdough can be cultivated in bakeries or obtained from commercial suppliers. In Belgium, many artisan bakeries still use spontaneously fermented sourdoughs, which are kept metabolically active through the addition of flour and water at regular intervals (backslopping). During this process of continuous propaga...
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