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Journal of Dairy Science Vol. 48 No. 11 1441-1444
© 1965 by American Dairy Science Association ®
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Activity of Lactic Streptococci Following Storage at Refrigeration Temperatures1

E. A. Cowman and M. L. Speck

Department of Food Science, North Carolina State University, Raleigh

ABSTRACT

The effect of aging at 3 C on cell viability, residual proteinase activity, and acid production was determined on single-strain cultures of Streptococcus lactis. Cell viability, as determined by colony counts, remained relatively constant during the first six days of storage; a slight decrease occurred after ten days. The proteinase activity of stored cells decreased with increased storage time (six days) until a relatively constant residual amount (12–16%) remained. The marked reduction during the first and second days of storage indicated high lability of the proteinase systcm to storage at refrigeration temperatures. No apparent relationship existed between reduction in enzymatic activity and cell viability. Acid production by the strains when cultured in milk at 22 C following storage for three days was considerably less than that by unstored cells. Further extension of storage resulted in a gradual reduction in the rate of acid production by the cells. The rate of acid production by aged cells when cultured in milk could be restored completely by addition of 0.2% pancreas extract.

FOOTNOTES

1 Contribution from the Food Science Department, North Carolina Agricultural Experiment Station, Raleigh, North Carolina. Published with the approval of the Director of Research as Paper no. 2037 of the Journal Series.






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Copyright © 1965 by the American Dairy Science Association ®.