Isolation and characterization of the microbial population of different South African kefir grains

Kefir, a slightly acidic fermented milk, is produced by adding lactic acid bacteria and yeasts, in the form of grains, to milk. The bacteria and yeasts present in the kefir grains are known to vary widely. Selective growth media and morphological and biochemical characteristics were used for the isolation and identification of the microbes present in the grains from eight different sources in South Africa. The kefir grains were activated in milk for only 24 h to prevent any changes in the microbial population of the grains. The microbial numbers varied between 6.4 x 10(4)and 8.5 x 10(8) cfu/g on the media selective for the bacterial species and between 1.5 x 10(5)and 3.7 x 10(8) cfu/g on the media selective for the yeast species. The bacterial genera that were identified included Lactobacillus, Leuconostoc and Lactococcus and the yeast genera included Zygosaccharomyces, Candida and Saccharomyces. The distribution frequencies of the microbes in the different grains were determined and most of the grains were dominated by two microbial species. No pediococci, acetic acid bacteria or propionibacteria were detected.