EFFECT OF POLYMERS AND STORAGE-TEMPERATURE ON THE STABILITY OF FREEZE-DRIED LACTIC-ACID BACTERIA

The effect of the addition of gelatin, xanthan gum or maltodextrins on the survival during freeze-drying and stability during storage of fou r lactic acid bacteria were studied. The polymers were added to a milk -sucrose base medium and mixed with the cell concentrate. The water ac tivity of the cultures was adjusted to 0.22 prior to storage at -20, 4 or 20 degrees C. None of the polymers generated marked improvement of the milk-sucrose medium in terms of survival of bacteria during freez e-drying. There were significant differences in mortality rates betwee n strains. Gelatin improved the storage stability of freeze-dried Lact obacillus casei ssp. rhamnosus RO11 and Bifidobacterium longum RO23 cu ltures kept at 20 and 4 degrees C, respectively. Also, bacterial popul ations of Lactococcus lactis ssp. lactis RO58, following 12 months at 4 degrees C, were higher than controls when gelatin was added to the f reeze-drying medium. Overall, the additives had a detrimental effect o n the stability of Streptococcus thermophilus RO57 during storage at 2 0 degrees C. The B. longum RO23 alpha- and beta-galactosidase activity losses during storage at 20 degrees C were approximately twice those observed at 4 and -20 degrees C, while viable count losses at 20 degre es C were approximately 100x greater than those at 4 degrees C. Copyri ght (C) 1996 Published by Elsevier Science Ltd on behalf of the Canadi an Institute of Food Science and Technology