The microbial stability of two bakery sourdoughs made from conventionally and organically grown rye Original Research Article

In order to determine the microbial stability of sourdoughs, two bakery sourdoughs made from conventionally and organically grown rye, produced on a large production scale under defined conditions, were studied at regular intervals over a period of 7 months. The sourdoughs contained lactic acid bacteria at levels of 8·43–9·14 log10cfu g−1and yeasts at levels of 6·00–8·04 log10cfu g−1. The number of lactic acid bacteria seemed to increase and the number of yeast to decrease with increasing fermentation time. Four types (A–D) of lactic acid bacteria dominated in both sourdough systems. Their frequencies varied during the sampling period, but seemed to follow the same trend in both systems. Identification based on API 50CH assimilation profiles, classical identification methods and 16S ribosomal DNA sequencing showed that the lactic acid bacteria contained in the two sourdough systems not clearly belonged to any known species of the genus Lactobacillus. Saccharomyces cerevisiae was the only yeast species isolated from the sourdoughs, represented by different phenotypes. In the conventional sourdough system one phenotype dominated throughout the sampling period. In the organic sourdough the phenotype changed after 3 months.