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Appl Environ Microbiol. 1972 October; 24(4): 551-554
Copyright © 1972 American Society for Microbiology. All Rights Reserved.

Death of Lactobacillus bulgaricus Resulting from Liquid Nitrogen Freezing¹

^a Department of Food Science, North Carolina State University, Raleigh, North Carolina 27607

ABSTRACT

Concentrated cell suspensions of Lactobacillus bulgaricus prepared from cells grown in semisynthetic media were frozen in liquid nitrogen. After storage for 24 hr, the cell suspensions were found to have decreased colony counts and acid-producing capacity in milk. The amount of loss varied among the different strains tested. The addition of known cryoprotective agents to cell suspensions of the most labile strain before freezing provided little or no protection to the cells. However, storage stability of all strains investigated was improved by supplementing the growth medium with Tween 80 (polyoxyethylene sorbitan monooleate). The concentration of Tween 80 necessary for maximal storage stability varied among strains.

¹ Paper no. 3783 of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh.