Interactions between Streptococcus thermophilus and Lactobacillus delbrueckii subsp bulgaricus used as starter cultures for the production of yogurt

The interactions, including symbiosis and antagonism between Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus strains were discussed. The mechanism causing unbalance growth of strains from the two species was stated based on the release of antagonistic compounds like peroxides hydro-gen and bacteriocins. A renewed system was established to evaluate the interactions among the strains of yo-gurt starter. The new criteria might be helpful in selecting strains to be used as yogurt starter culture.