Lactic acid bacteria constitute the main part of the microbial flora of food fermentaions. Cereal fermentations are mainly dominated by the genus Lactobacillus. Sourdough fermentations are grouped into three so-called types (type I-III), reflecting the numerous internal and external fermentation parameters. In turn, they exert influence on the composition of the microflora. Lactobacillus sanfranciscensis is one of the most prominent species found in type I doughs, while species like L. pontis, L. panis, L. reuteri, L. fermentum and L. amylovorus are found in type II doughs. Type III doughs are dominated by species like L. plantarum, L. brevis or Pediococcus pentosaceus. Classically, the chracterization of lactic acid bacteria is based on phenotypical properties, leading to an identification of the bacteria. Such properties are, the fermentaion of certain carbohydrates, to cleave certain substrates or simply their macroscopic/ microscopic shape. Lactic acid bacteria from the sourdough environment are strongly adapted to their environment, thus a identification on the mentioned approach is often leading to ambigous results. Furthermore, a routine identification is hampered by their poor growth on synthetic media, caused by their adaption to the sourdough environment. In this work identification methods focusing the genotype of lactic acid bacteria are presented, to circumvent these problems. These methods are targeted on nucleic acids, and in here the 16S rRNA. For an improved identification procedure a PCR protocol based on these data was developed for the fast and reliable identification of L. pontis, L. panis and L. frumenti, which was described as a new species. The combination of these PCR procedure together with a DNA extraction method directly from the sourdough led to a further acceleration of the identification without the necessity of a cultivation step. A further PCR based technique developed in this work is the generation of DNA fingerprints by RAPD-PCR. Applying this method, the understanding of the microbial ecology of such fermentations was markedly improved. The fermentation flora of an industrial type II fermentation was investigated, grouping isolates from independent fermentations into genotypes by RAPD-PCR. It could be demonstrated, that such fermentations conducted under non-sterile conditions remain remarkly constant, with a composition of 70% L. amylovorus, 30% L. pontis and L. frumenti and in a few cases L. reuteri. Beside the characterization of lactic acid bacteria, RAPD-PCR revealed appropriate also for the characterization of yeast species. 45 yeast strain were isolated from various traditionally propagated sourdoughs and subsequently typed by RAPD-PCR. All isolates could be grouped into three clusters, and by including reference strains they were identified as Saccharomyces cerevisiae, Yarrowia lipolytica and Pichia membranaefaciens. These results were confirmed by FT-IR spectroscopy, SDS-PAGE and physiological investigations. 16S rDNA sequencing with subsequent comparative sequence analysis revealed as the gold standard for a reliable identification of new isolates from sourdough. Numerous strains from type II fermentations couldn't be assorted to already classified species in a phylogenetic tree. The most closest neighbours were L. vaginalis, L. oris, L. pontis, L. panis and L. reuteri. More detailed investigations regarding physiology, chemotaxonomic properties, G +C content and DNA-DNA homolgy showed the idependent status of this species, recently described as L. frumenti.     «

Lactic acid bacteria constitute the main part of the microbial flora of food fermentaions. Cereal fermentations are mainly dominated by the genus Lactobacillus. Sourdough fermentations are grouped into three so-called types (type I-III), reflecting the numerous internal and external fermentation parameters. In turn, they exert influence on the composition of the microflora. Lactobacillus sanfranciscensis is one of the most prominent species found in type I doughs, while species like L. pontis, L...     »