Characterization of the bacterial flora of Sudanese sorghum flour and sorghum sourdough.

The microflora of a Sudanese sorghum flour, a spontaneously fermented sourdough and a long-term sourdough produced in a Sudanese household by consecutive re-inoculations, was studied. The dominant contaminants of sorghum flour were Gram-negative, catalase-positive, rod-shaped bacteria with counts of about 10(5) cfu g-1. The spontaneously fermented sorghum sourdough showed a bacterial succession from Gram-negative, catalase-positive contaminants to Enterococcus faecalis, Lactococcus lactis, Lactobacillus fermentum and Lact. reuteri. The total bacterial count reached about 10(10) cfu g-1 and the pH dropped from 6.4 to 3.35 in about 42 h. In this phase, only the Latter two species remained dominant in a ratio of 1:1. From the Sudanese long-term dough, seven strains of Lactobacillus were isolated, representing the dominant flora. Sequence comparison of partial 16S rRNA gene sequences were used to clarify their phylogenetic positions. Five strains were classified as Lact. vaginalis and could be regarded as heterogeneous biovars of this species. The other two strains could be assigned to Lact. helveticus. RAPD-PCR and sugar fermentation patterns were useful in differentiation of these strains.