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One of the traditional ways of preparation of yogurt starter in Bulgaria is placing a branch of a particular plant species into boiled sheep's milk maintained at about 45 degrees C, which is further incubated until a dense coagulum is obtained. To investigate the possible origin of the yogurt starter bacteria, Lactobacillus delbrueckii ssp. bulgaricus (L. bulgaricus) and Streptococcus thermophilus (S. thermophilus), the traditional way of yogurt-starter preparation was followed. Hundreds of plant samples were collected from four regions in Bulgaria and incubated in sterile skim milk. The two target bacteria at low frequencies from the plant samples collected were successfully isolated. Phenotypic and genotypic characteristics of these bacterial isolates revealed that they were identified as L. bulgaricus and S. thermophilus. Twenty isolates of L. bulgaricus and S. thermophilus, respectively, were selected from the isolated strains and further characterized with regard to their performance in yogurt production. Organoleptic and physical properties of yogurt prepared using the isolated strains from plants were not significantly different from those prepared using commercial yogurt-starter strains. It was therefore suggested that L. bulgaricus and S. thermophilus strains widely used for commercial yogurt production could have originated from plants in Bulgaria. To our knowledge, this is the first report on the isolation and characterization of L. bulgaricus and S. thermophilus strains from plants.

The effect of a culture powder of Propionibacterium freudenreichii ET-3 cells containing a bifidogenic growth stimulator (BGS) on fecal flora was studied in twelve healthy subjects with a mean age of 42.6 (range, 27-56 years). One gram of BGS powder containing 17.4 U of BGS activity was administered for 14 days, three times a day after meals. A significantly higher number of bifidobacteria in fecal samples was observed during the intake period of the BGS powder. The frequency of occurrence of the bifidobacteria also increased from 92% to 100%. These results indicate that the BGS acts in the intestine as a growth stimulator of bifidobacteria when the BGS powder is administered.

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