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Appl Environ Microbiol. 1974 April; 27(4): 738-743
Copyright © 1974 American Society for Microbiology. All Rights Reserved.

Relationship of Cellular Fatty Acid Composition to Survival of Lactobacillus bulgaricus in Liquid Nitrogen¹

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

ABSTRACT

Concentrated cultures of Lactobacillus bulgaricus were prepared by resuspending cells grown in semisynthetic media in sterile 10% non-fat milk solids. The concentrated cultures were frozen in liquid nitrogen for 24 h. The cell suspensions exhibited decreased viability after storage, and the amount of death varied among the different strains tested. Storage stability of all strains examined was improved by supplementing the growth medium with sodium oleate. Radioisotopes were used to study the fate of sodium oleate with L. bulgaricus NCS1. [1-¹⁴C]sodium oleate was incorporated solely into the lipid portion of the cells, including both neutral and polar lipids. The fatty acid composition of L. bulgaricus NCS1, NCS2, NCS3, and NCS4 grown with and without sodium oleate was studied. The major fatty acids of strains NCS1, NCS2, and NCS3 grown without sodium oleate were dodecanoic, tetradecanoic, hexadecanoic, hexadecenoic, and octadecenoic acids. In addition to these, strain NCS4 contained C₁₉ cyclopropane fatty acid. The major fatty acids of all strains grown with sodium oleate were tetradecanoic, hexadecanoic, hexadecenoic, octadecenoic, and C₁₉ cyclopropane fatty acids. All strains grown in broth containing sodium oleate contained larger amounts of octadecenoic and C₁₉ cyclopropane fatty acid, and less saturated fatty acids than when grown without sodium oleate. Statistical analyses indicated that C₁₉ cyclopropane fatty acid was most closely related to stability of the lactobacilli in liquid nitrogen. A negative regression line that was significant at P < 0.001 was obtained when the cellular content of this fatty acid was plotted against death.

¹ Paper no. 4145 of the Journal Series of the North Carolina State Univ. Agricultural Experiment Station, Raleigh, N. C.