Application of the accelerated shelf life testing method (ASLT) to study the survival rates of freeze-dried Lactococcus starter cultures

The survival rates of two freeze-dried strains, Lactococcus lactis var diac etylactis and Lactococcus lactis var lactis, were evaluated using the Accel erated Shelf Life Testing (ASLT) method. The strains were initially isolate d from a brand of a Tunisian fermented milk product. Lactococcus cell survi val observed at higher temperatures was used to extrapolate to shelf life a t a lower storage temperature of 4 degreesC. The apparent kinetics of the s urvival rate loss were estimated and the effect of storage temperature was quantified by determining the inactivation energies for various samples. Th e work has shown an overall higher survival rate of the strain Lactococcus lactis var diacetylactis. An average half-life of a strain maintained at 25 degreesC was equal to about 7 days as compared with about 43 days at 4 deg reesC. The addition of lyoprotectants such glycerol, saccharose and calcium carbonate to the drying medium, improved the survival of such bacteria. (C) 2001 Society of Chemical Industry.