This work was undertaken to characterize the interaction between Bifidobacterium longum DSM 20097 and 6
strains of lactic acid bacteria belonging to Streptococcus thermophilus, Lactococcus lactis subsp. lactis, Lactobacillus
delbrueckii subsp. bulgaricus, Lactobacillus casei subsp. paracasei, Lactobacillus acidophilus and Lactobacillus
plantarum. Bifidobacterium longum was grown in sterilized skim milk supplemented with 2% glucose, 1% yeast
extract and 0.05% L-cysteine hydrochloride either separately or in co-culture with one of the above listed strains of
lactic acid bacteria. Following 18 hr of incubation at 37°C, milk cultures were stored at 5±1°C for 28 days. Changes in
titratable acidity, pH, organic acids, soluble tyrosine, viable counts and antibacterial activity of various milk cultures
were monitored at regular intervals during refrigeration storage. Results revealed that B. longum survived better in the
presence of Lb. plantarum, while its viability was drastically declined in the presence of Lb. bulgaricus. Among tested
lactic acid organisms, Lb. plantarum proved to be the highest proteolytic organism, determined in terms of soluble tyrosine,
and the least acid producer. These activities might be responsible for the improvement of viability of B. longum
during refrigeration storage. Also, combining B. longum with Lb. plantarum improved the antimicrobial activity of the
former against Staphylococcus aureus and Bacillus subtilis as assessed by the well-diffusion agar method