Cryotolerance of Lactobacillus delbrueckii subsp. bulgaricus CFL1 is influenced by the physiological state during fermentation

To better understand the effects of freezing and frozen storage on different characteristics of the cell state, the influence of the physiological state, as defined by fermentation pH and harvesting time, and the freezing medium on the cryotolerance of Lactobacillus bulgaricus CFL1 was investigated. Esterase activity, membrane integrity, cultivability and acidification activity were quantified during culture with and without pH control, and during freezing and frozen storage at −20 °C. The preservation of esterase activity and membrane integrity was not related to starter functionalities such as cultivability and acidification activity. Cell cryotolerance increased with fermentation time or when cells were harvested during culture at pH 5 and frozen, as compared with fermentations at pH 6 or without pH control. Long-term cell cryotolerance could be predicted by determining an early physiological parameter such as a low initial acidification activity when the cells are harvested.