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Journal of Dairy Science Vol. 69 No. 10 2558-2568
© 1986 by American Dairy Science Association ®
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Influence of Temperature on Associative Growth of Streptococcus thermophilus and Lactobacillus bulgaricus1

Lyn C. Radke-Mitchell2 and W. E. Sandine

Department of Microbiology, Oregon State University, Corvallis 97331-3804

ABSTRACT

Compatibility of Streptococcus thermophilus and Lactobacillus bulgaricus during associative growth as dependent on optimum growth temperature was determined. Optimum growth temperatures for 9 strains of S. thermophilus and 10 strains of L. bulgaricus ranged from 35 to 42°C for S. thermophilus and 43 to 46°C for L. bulgaricus. Streptococcus thermophilus and L. bulgaricus strains exhibiting similar to divergent optimum growth temperatures were combined (1:1 vol/vol) and incubated in milk at 37, 42, and 45°C until pH 4.2 was reached. Initial and postincubation cell numbers were determined by plate count method. Streptococcus thermophilus strains reached greater cell numbers than L. bulgaricus at 37, 42, and 45°C in 93.3% of the mixed culture trials. Average rod-coccus ratios obtained at 37, 42, and 45°C were 1:2.2, 1:8, and 1:2.4, respectively. Optimum growth temperatures had no influence on growth of L. bulgaricus and S. thermophilus in mixed culture. Rather, temperature appeared to influence compatibility by determining the concentration or type of stimulatory factor(s) produced by L. bulgaricus. All strains of S. thermophilus exhibited an uncoupling of growth from acid production. Optimum temperature for acid production ranged from 2 to 8°C above optimum growth temperature. These findings warrant consideration in the manufacture of yogurt and other fermented milk products.

FOOTNOTES

1 Technical Paper Number 7473, Oregon Agricultural Experiment Station.

2 Bend Research, Inc., Bend, OR 97701.






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Copyright © 1986 by the American Dairy Science Association ®.