Study of the cryotolerance of Lactobacillus acidophilus: effect of culture and freezing conditions on the viability and cellular protein levels.

Slow cooling rate and pre-freezing stress brings about a high increase in the cell resistance and preservation of their physiological characteristics. A brutal decrease in temperature (from 37 degrees C to - 80 degrees C) causes a considerable loss of cell viability, in contrast a slow one preserves a survival rate of 75%. Pre-incubation of cells at low temperature (22 degrees C) during 6 h led to the development of cryotolerance indicated by an enhanced capacity to survive after a freezing treatment of 24 h at - 80 degrees C. Exposure of the cells to low pH (5.5) caused a large decrease in cell resistance but did not lead to any significant decrease of survival rate after freezing treatment. However, an increase of 15 +/- 3% in protein level compared to cells cultivated at regulated pH was observed.