Accelerated storage testing of freeze-drying Pseudomonas fluorescens BTP1, BB2 and PI9 strains

Freeze-dried cultures of P.fluorescens are used in agriculture and microbiological industry. However, P. fluorescens is very susceptible to damage during freeze-drying and subsequent storage and it would be useful to increase culture viability during storage. The viability of freeze-dried P. fluorescens strains (BTP1, PI9 and BB2) was evaluated by using the Arrhenius model. This model was described by measuring of reaction rate constants (D or k) and temperature sensitivity of rate constant (z or Ea). The freeze-dried P.fluorescens strains was stored in glass tubes at 60°C, 37°C and 4°C for 8 h, 28 days and 2 months, respectively. D value decreased or k increased with an increase of the storage temperature. By comparing their decimal reduction time (D), we observed that BB2 strain was more resistant than BTP1 and PI9 at 37 °C and 60 °C. The activation energy of all P. fluorescens strains are not significantly different and thermal inactivation may occur by the same mechanism. Thus it was possible to compare rate constants of survival for the freeze-dried P. fluorescens strains. These results will be useful to the development of improved reference materials and samples held in culture collections.