A comparison of beta-galactosidase specific activities in strains of Streptococcus thermophilus

Six Streptococcus thermophilus strains were examined for growth, acid production, and beta-galactosidase activity per milligram protein (specific activity), so that strain comparisons could be made. A wide range in activity was observed. Activity depended on growth time in M17 broth and, for most strains, continued to increase after cells had reached stationary phase. Maximum activity was at 16 h and ranged from 0 to 58 units/mg protein. Strain ST exhibited no beta-galactosidase activity but had trace phospho-beta-galactosidase activity (.8 units/mg protein after 2 h of growth). Strains 3641 and TS2B exhibited slower growth rates and lower beta-galactosidase activities in milk as compared to M17 broth. Further, strain 3641 exhibited 10 times the activity of strain TS2B (2.86 vs. .24 units) after 4 h of growth in milk.