Characterisation of the dominant microbiota of Sudanese fermented milk Rob

The predominant microorganisms in the Sudanese traditional fermented dairy product Rob from cows' milk were isolated and identified by using morphological, physiological and molecular typing techniques. From seven production sites in Khartoum, samples of Rob used as inocula for fermentation were analysed by the determination of the cfu mL(-1) on MRS, M17, potato dextrose agar and plate count agar. Samples of inocula from two production sites were used for Rob fermentation in the laboratory followed by similar microbiological analysis. The results obtained showed that the Rob inocula contained lactococci and lactobacilli in the range of 10(7)-10(8) and yeasts in the range of 10(6)-10(7) cfu mL(-1). During the course of the two laboratory fermentations, the lactococci and lactobacilli increased to 10(8) cfu mL(-1), the yeasts to 10(7) cfu mL(-1) and the aerobic mesophilic counts decreased to 10(5) cfu mL(-1). The pH of the inocula ranged between 3.4 and 3.6 and the pH of Rob produced in the laboratory was 4.2-4.5. Using the internal transcribed spacer-polymerase chain reaction (PCR) technique, 189 representative strains of lactic acid bacteria and 109 representative isolates of yeasts were divided into nine and two groups, respectively, according to the size of the PCR product formed. Representative members of all groups were identified by the API 50 CH and the ID 32 API kits for lactic acid bacteria and yeasts, respectively. Confirmation of identification of lactic acid bacteria species was achieved by sequencing the 16S rRNA gene. The predominant lactic acid bacteria in Rob fermentation were found to be Lactobacillus frementum, Lactobacillus acidophilus, Lactococcus lactis, and Streptococcus salivarius. The predominant yeasts were found to be Saccharomyces cerevisae and Candida kefyr. (C) 2001 Elsevier Science Ltd. All rights reserved.