Abstract

The fitness of a particular strains of Bifidobacteria, Lactobacilli and Streptococci for commercial utilization depends on its rapid growth and acidification of milk as well as its acid and oxygen tolerence. From 20 samples of French commercial yoghurt, one species of bifidobacteria was identified as Bifidobacterium longum. Also,Lactobacillus acidophilus was isolated and identified from fermented milk. The rate of growth was 0.37 h^-1 on TPY medium and 0.18 h^-1 in milk with Bifidobactrium longum. The production of lactic acid was compared with pure and mixed cultures and the values were 90 and 64 mM at 37°C; 82 and 140 mM at 45°C. The maximum rate of lactic acid production was obtained with mixed culture at 45°C.

Key words: Bifidobacterium longum, Lactobacillus acidophilus, fermented milk, growth, lactic acid.