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A Comparison of Beta-Galactosidase Specific Activities in Strains of Streptococcus thermophilus^{1, 2,}

Department of Food Science and Nutrition, University of Minnesota, 1334 Eckles Avenue St. Paul 55108

ABSTRACT

Six Streptococcus thermophilus strains were examined for growth, acid production, and ß-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 ß-galactosidase activity but had trace phospho-ß-galactosidase activity (.8 units/mg protein after 2 h of growth). Strains 3641 and TS2B exhibited slower growth rates and lower ß-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.

¹ Published as Paper Number 14,644 of the Scientific Series of the Minnesota Agricultural Experiment Station on research conducted under the Minnesota Experiment Station Project Numbers 18-016 and 18-hi.

² This project was funded by the National Dairy Board and administered in cooperation with the Dairy Research Foundation.