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.

Weckx S ，Van der Meulen R ，Maes D ，Scheirlinck I ，Huys G ，Vandamme P ，De Vuyst L ... -  《-》

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

Van der Meulen R ，Scheirlinck I ，Van Schoor A ，Huys G ，Vancanneyt M ，Vandamme P ，De Vuyst L ... -  《-》

Prevalence and impact of single-strain starter cultures of lactic acid bacteria on metabolite formation in sourdough.

Flavour of type II sourdoughs is influenced by the ingredients, processing conditions, and starter culture composition. It is, however, not fully clear to what extent different sourdough lactic acid bacteria (LAB) contribute to flavour. Therefore, two types of flour (rye and wheat) and different LAB starter culture strains were used to prepare sourdoughs, thereby leaving the yeast microbiota uncontrolled. All LAB starter culture strains tested were shown to be prevalent and to acidify the flour/water mixture to pH values between 3.1 and 3.9 after 24h of fermentation. Multiple aldehydes, alcohols, ketones, and carboxylic acids were produced by the sourdough-associated microbiota throughout the fermentation period. Based on the organoleptic evaluation of breads produced with these sourdoughs, five LAB strains were selected to perform prolonged wheat and rye fermentations as to their capacity to result in an acidic (Lactobacillus fermentum IMDO 130101, Lactobacillus plantarum IMDO 130201, and Lactobacillus crustorum LMG 23699), buttermilk-like (Lactobacillus amylovorus DCE 471), or fruity flavour (Lactobacillus sakei CG1). Upon prolonged fermentation, higher metabolite concentrations were produced. For instance, L. sakei CG1 produced the highest amounts of 3-methyl-1-butanol, which was further converted into 3-methylbutyl acetate. The latter compound resulted in a fruity banana flavour after 48h of fermentation, probably due to yeast interference. Rye fermentations resulted in sourdoughs richer in volatiles than wheat, including 3-methyl-1-butanol, 2-phenylethanol, and ethyl acetate.

Ravyts F ，De Vuyst L 《-》

Impact of ecological factors on the stability of microbial associations in sourdough fermentation.

The limits for the stability of the microbial association 1 (Lactobacillus sanfranciscensis and Candida humilis) and association 2 (Lactobacillus reuteri, Lactobacillus johnsonii and Issatchenkia orientalis) during sourdough fermentation were evaluated by investigating the effects of the ecological factors substrate, refreshment time, temperature, amount of backslopping and competing species in different combinations on their growth. Sourdoughs were fermented in 28 batches under different conditions using the associations and possible competing strains as starters. The dominating microbiota was characterized by bacteriological culture, rRNA gene sequence analysis and RAPD-PCR. Association 1 was found to be competitive in doughs with rye and wheat flour at temperatures between 20 and 30 °C, refreshment times of 12 and 24 h, amounts of backslopping dough from 5 to 20% and against all competing lactic acid bacteria and yeasts. The processing parameters for the competitiveness of the association 2 were temperatures of 35-40 °C, refreshment times of 12-24 h and the substrates rye bran, wheat and rye flour, but not in every case. Issatchenkia orientalis could only grow when enough oxygen was available. Its cell counts fell rapidly under the limit of detection when using high amounts of doughs (small ratio of surface to volume) and refreshment times of 12 h. In conclusion, the results demonstrated that the two associations were remarkably stable under most of the investigated process conditions.

Vogelmann SA ，Hertel C 《-》

Robustness of Lactobacillus plantarum starters during daily propagation of wheat flour sourdough type I.

This study aimed at investigating the robustness of selected sourdough strains of Lactobacillus plantarum. Seven strains were singly used as sourdough type I starters under daily back-slopping propagation (ten days) using wheat flour. Cell numbers of presumptive lactic acid bacteria varied slightly (median values of 9.13-9.46 log cfu g(-1)) between and within started sourdoughs, as well as the acidifying activity (median values of 1.24-1.33). After three days also the control sourdough (unstarted) had the same values. As shown by RAPD-PCR analysis, five (DB200, 3DM, G10C3, 12H1 and LP20) out of seven strains maintained elevated cell numbers (ca. 9 log cfu g(-1)) throughout ten days. The other two strains progressively decreased to less than 5 log cfu g(-1). As identified by partial sequencing of 16S rRNA and recA genes, L. plantarum (11 isolates), pediococci (7), Lactobacillus casei (3) and Lactobacillus rossiae (2) dominated the flour microbiota. Monitoring of lactic acid bacteria during sourdough propagation was carried out by culture dependent approach and using PCR-DGGE (Denaturing Gradient Gel Electrophoresis). Except for the sourdough started with L. plantarum LP20, in all other sourdoughs at least one autochthonous strain of L. plantarum emerged. All emerging strains of L. plantarum showed different RAPD-PCR profiles. L. rossiae and Pediococcus pentosaceus were only found in the control and sourdough started with strain 12H1. The characterization of the catabolic profiles of sourdoughs (Biolog System) showed that sourdoughs containing persistent starters behaved similarly and their profiles were clearly differentiated from the others. One persistent strain (DB200) of L. plantarum and Lactobacillus sanfranciscensis LS44, previously shown to be persistent (Siragusa et al., 2009), were used as the mixed starter to produce a wheat flour sourdough. Both strains cohabited and dominated during ten days of propagation.

Minervini F ，De Angelis M ，Di Cagno R ，Pinto D ，Siragusa S ，Rizzello CG ，Gobbetti M ... -  《-》