Optimisation of production and storage stability of the starter bacteria Streptococcus thermophilus and Lactobacillus plantarum

The growth of Lactobacillus plantarum and Streptococcus thermophilus was modelled by fitting isothermal calorimetric traces to arbitrary mathematical functions. There was a correlation between certain features on the thermal trace and parameters derived from a Baranyi fit to viable count data. In the presence of 75 g L −1 lactose, S. thermophilus showed a slower rate of growth than in the presence of 5 g L −1 lactose when measured by both viable count and heat flow. A simple equation described the variation in glass transition temperature with water activity for all preparations. A master curve fit for all mortality data for S. thermophilus showed the importance of a transition temperature for the survival of freeze‐dried preparations of bacteria. The temperature at which survival began to be impaired was 15–20 °C below the glass transition temperature determined by differential scanning calorimetry. Copyright © 2007 Society of Chemical Industry