Survival of Lactobacillus bulgaricus During Freezing and Freeze‐Drying After Growth in the Presence of Calcium

Two morphologically distinct isolates of L. bulgaricus 1243 (designated F and O), were examined for stability during freezing and freeze‐diying following growth in a nutrient broth medium supplemented with varying concentrations of calcium. While cellular morphology did not influence survival during −20°C frozen storage, calcium prevented freezing death in both isolates. Maximum survival occurred at calcium concentrations ranging between 5.4 × 10 −3 and 6.7 × 10 −3 M. Calcium supplemented L. bulgaricus 1243‐F displayed a five‐fold decline in viable count (3.2 × 10 8 to 6.1 × 10 7 ) due to −20°C freezing, compared with cells propagated in broth without calcium, which declined 200‐fold (1.7 × 10 8 to 6.3 × 10 5 ). Mg ++ and Mn ++ salts failed to exert protective effects. Calcium was ineffective in preventing freeze‐injury, since cells displayed decreased acid production in milk following −20°C storage.