The Viability of Dried Skim-Milk Cultures of Lactobacillus bulgaricus as Affected by the Temperature of Reconstitution

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Abstract
In spray-dried cultures of L. bulgaricus a large number of cells that failed to grow when the temp. of the reconstituting fluid was 21-25[degree]C were ac-tivated sufficiently to produce normal growth when the temp. of the reconstituting fluid was 37-50[degree]C. When the culture was reconstituted at 21-25[degree]C and warmed to 50[degree]C the activating effect of the heat was not obtained. The in-crease in the colony count resulting from reconstitution at 50[degree]C over reconstitution at 21-25[degree]C could not be explained by an increase in the solubility of the powder, nor an increase in the dispersion of the cells. Reconstitution of dried L. bulgaricus at 50 [degree]C with subsequent inoculation into skimmilk showed greater activity in the skimmilk, particularly in the early stages of growth, than was obtained when the culture was reconstituted at 21-25 [degree]C. Freeze-drying part of a skimmilk culture that was also spray-dried showed that cells in the freeze-dried culture were not only not activated by reconstitution at 50[degree]C but that this temp. actually was lethal to many of the cells. This suggested a physiological difference between freeze-dried and spray-dried cells of L. bulgaricus, since the latter were markedly activated by heat.