Study of the Fermentation Characteristics of Non-Conventional Yeast Strains in Sweet Dough.

Despite the diverse functions of yeast, only a relatively homogenous group of Saccharomyces cerevisiae yeasts is used in the baking industry. Much of the potential of the natural diversity of yeasts has not been explored, and the sensory complexity of fermented baked foods is limited. While research on non-conventional yeast strains in bread making is increasing, it is minimal for sweet fermented bakery products. In this study, the fermentation characteristics of 23 yeasts from the bakery, beer, wine, and spirits industries were investigated in sweet dough (14% added sucrose w/w dm flour). Significant differences in invertase activity, sugar consumption (0.78-5.25% w/w dm flour), and metabolite (0.33-3.01% CO2; 0.20-1.26% ethanol; 0.17-0.80% glycerol; 0.09-0.29% organic acids) and volatile compound production were observed. A strong positive correlation (R2 = 0.76, p < 0.001) between sugar consumption and metabolite production was measured. Several non-conventional yeast strains produced more positive aroma compounds and fewer off-flavors than the reference baker's yeast. This study shows the potential of non-conventional yeast strains in sweet dough.

Sugar Levels Determine Fermentation Dynamics during Yeast Pastry Making and Its Impact on Dough and Product Characteristics.

Fermented pastry products are produced by fermenting and baking multi-layered dough. Increasing our knowledge of the impact of the fermentation process during pastry making could offer opportunities for improving the production process or end-product quality, whereas increasing our knowledge on the sugar release and consumption dynamics by yeast could help to design sugar reduction strategies. Therefore, this study investigates the impact of yeast fermentation and different sugar concentrations on pastry dough properties and product quality characteristics. First, yeasted pastry samples were made with 8% yeast and 14% sucrose on a wheat flour dry matter base and compared to non-yeasted samples. Analysis of saccharide concentrations revealed that sucrose was almost entirely degraded by invertase in yeasted samples after mixing. Fructans were also degraded extensively, but more slowly. At least 23.6 ± 2.6% of the released glucose was consumed during fermentation. CO2 production during fermentation contributed more to product height development than water and ethanol evaporation during baking. Yeast metabolites weakened the gluten network, causing a reduction in dough strength and extensibility. However, fermentation time had a more significant impact on dough rheology parameters than the presence of yeast. In balance, yeast fermentation did not significantly affect the calculated sweetness factor of the pastry product with 14% added sucrose. Increasing the sugar content (21%) led to higher osmotic stress, resulting in reduced sugar consumption, reduced CO2 and ethanol production and a lower product volume. A darker colour and a higher sweetness factor were obtained. Reducing the sugar content (7%) had the opposite effect. Eliminating sucrose from the recipe (0%) resulted in a shortened productive fermentation time due to sugar depletion. Dough rheology was affected to a limited extent by changes in sucrose addition, although no sucrose addition or a very high sucrose level (21%) reduced the maximum dough strength. Based on the insights obtained in this study, yeast-based strategies can be developed to improve the production and quality of fermented pastry.

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

Ting is a spontaneously fermented sorghum food that is popular for its sour taste and unique flavour. Insight of the microbial diversity and population dynamics during sorghum fermentations is an essential component of the development of starter cultures for commercial production of ting. In this study, bacterial populations associated with spontaneous sorghum fermentations were examined using a culture-independent strategy based on denaturing gradient gel electrophoresis and sequence analysis of V3-16S rRNA gene amplicons, and a culture-dependent strategy using conventional isolation based on culturing followed by 16S rRNA and/or pheS gene sequence analysis. The entire fermentation process was monitored over a 54 h period and two phases were observed with respect to pH evolution and microbial succession. The first phase of the process (0-6h) was characterized by relatively high pH conditions and the presence of Enterococcus mundtii, albeit that this species was only detected with the culture-dependent approach. The second phase of the fermentation process (12-54 h) was characterized by increased acidity and the predominance of a broader range of lactic acid bacteria, including Lactococcus lactis, Lactobacillus fermentum, Lactobacillus plantarum, Lactobacillus rhamnosus, Weissella cibaria, Enterococcus faecalis, and a close relative of Lactobacillus curvatus, as well as some members of the Enterobacteriaceae family. The Lb. curvatus-like species was only detected with PCR-DGGE, while the majority of the other species was only detected using the culture-dependent approach. These findings highlighted the fact that a combination of both approaches was essential in revealing the microbial diversity and dynamics during spontaneous sorghum fermentations.

Lactic acid bacteria community dynamics and metabolite production of rye sourdough fermentations share characteristics of wheat and spelt sourdough fermentations.

Four spontaneous rye sourdough fermentations were performed over a period of ten days with daily back-slopping. Samples taken at all refreshment steps were used for culture-dependent and culture-independent characterization of the microbiota present. Furthermore, an extensive metabolite target analysis was performed through a combination of various chromatographic methods, including liquid chromatography coupled to mass spectrometry (LC/MS) and gas chromatography coupled to mass spectrometry (GC/MS). Spearman's rank correlation coefficients were calculated and a principal component analysis (PCA) was performed on the data obtained in this study combined with data obtained previously for wheat and spelt sourdoughs. In general, the establishment of a stable microbial ecosystem occurred through a three-phase evolution, with mainly Lactobacillus plantarum and Lactobacillus fermentum dominating the rye sourdough ecosystems. PCA revealed that ornithine and mannitol were positively correlated with rye sourdoughs, contributing to bacterial competitiveness at the onset of sourdough production. Wheat and spelt sourdoughs showed a high degree of similarity, although certain compounds (e.g. indolelactic acid) appeared to be specific for spelt sourdoughs. The production of amino acid metabolites, mainly hydroxy acids (e.g. phenyllactic acid) and alcohols (e.g. 3-methyl-1-butanol), contributed to the equilibration of the redox balance and further enhanced the competitiveness of dominant species in stable sourdoughs.

Polyphasic taxonomic characterization of Lactobacillus rossiae isolates from Belgian and Italian sourdoughs reveals intraspecific heterogeneity.

(GTG)5-PCR fingerprinting and pheS sequence analysis of 18 Lactobacillus rossiae isolates, mainly originating from Belgian and Italian artisan sourdoughs, revealed intraspecies grouping as evidenced by the delineation of three and two subgroups, respectively. On the other hand, 16S rRNA and rpoA gene sequence analysis and DNA-DNA hybridizations supported the accommodation of all isolates in a single species. No correlation between genetic and phenotypic heterogeneity was observed. Collectively, these data do not warrant taxonomic division of L. rossiae. On the other hand, the considerable differences in intraspecies sequence variation of L. rossiae isolates displayed by the pheS (9.8%) and rpoA (1.1%) genes highlight that the discriminatory power of housekeeping genes as alternative genomic markers for the 16S rRNA gene in the identification of Lactobacillus species may significantly differ from gene to gene. In conclusion, this study has demonstrated that a polyphasic approach remains highly useful for identification of isolates belonging to genotypically heterogeneous species such as L. rossiae.

Taxonomic structure and stability of the bacterial community in belgian sourdough ecosystems as assessed by culture and population fingerprinting.

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 culture-independent 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.

Influence of geographical origin and flour type on diversity of lactic acid bacteria in traditional Belgian sourdoughs.

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.

Lactobacillus crustorum sp. nov., isolated from two traditional Belgian wheat sourdoughs.

A polyphasic taxonomic study of the lactic acid bacteria (LAB) population in three traditional Belgian sourdoughs, sampled between 2002 and 2004, revealed a group of isolates that could not be assigned to any recognized LAB species. Initially, sourdough isolates were screened by means of (GTG)(5)-PCR fingerprinting. Four isolates displaying unique (GTG)(5)-PCR patterns were further investigated by means of phenylalanyl-tRNA synthase (pheS) gene sequence analysis and represented a bifurcated branch that could not be allocated to any LAB species present in the in-house pheS database. Their phylogenetic affiliation was determined using 16S rRNA gene sequence analysis and showed that the four sourdough isolates belong to the Lactobacillus plantarum group with Lactobacillus mindensis, Lactobacillus farciminis and Lactobacillus nantensis as closest relatives. Further genotypic and phenotypic studies, including whole-cell protein analysis (SDS-PAGE), amplified fragment length polymorphism (AFLP) fingerprinting, DNA-DNA hybridization, DNA G+C content analysis, growth characteristics and biochemical features, demonstrated that the new sourdough isolates represent a novel Lactobacillus species for which the name Lactobacillus crustorum sp. nov. is proposed. The type strain of the new species is LMG 23699(T) (=CCUG 53174(T)).

Population dynamics and metabolite target analysis of lactic acid bacteria during laboratory fermentations of wheat and spelt sourdoughs.

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.

Lactobacillus namurensis sp. nov., isolated from a traditional Belgian sourdough.

A biodiversity study on lactic acid bacteria (LAB) occurring in traditional Belgian sourdoughs resulted in the isolation of two Lactobacillus isolates, LMG 23583T and LMG 23584, that could not be assigned to any recognized LAB species. The two isolates were initially investigated by means of phenylalanyl-tRNA synthase (pheS) gene sequence analysis and were found to occupy a separate position relative to recognized Lactobacillus species present in the pheS database. Subsequently, their phylogenetic affiliation was determined by 16S rRNA gene sequence analysis, indicating that the two isolates belong to the Lactobacillus buchneri species group with Lactobacillus zymae, Lactobacillus acidifarinae and Lactobacillus spicheri as closest relatives. Whole-cell protein analysis (SDS-PAGE) and amplified fragment length polymorphism fingerprinting of whole genomes confirmed their separate taxonomic status. DNA-DNA hybridization experiments, DNA G+C content, growth characteristics and biochemical features demonstrated that the two isolates represent a novel Lactobacillus species, for which the name Lactobacillus namurensis sp. nov. is proposed. The type strain is LMG 23583T (=CCUG 52843T).