ABSTRACT
The preservation of stock-cultures of microorganisms is prerequisite to a wide range of industrial and research applications. The essence of any preservation process is to provide a viable, stable preparation using simple, well-validated techniques which will assure a high probability of success and batch reproducibility. The criteria used to assess preservation efficacy are often taken as reproducibility, biochemical properties, and genetic stability. Microorganisms are much more thermostable in the freeze-dried form than in suspension, dried cultures are not immune to thermal inactivation, and storage at low temperatures will improve stability. Vacuum provides a favorable sealing environment for long-term stability of dried inocula and enables seal integrity to be tested using glow-discharge. Frozen inocula can be transported in solid carbon dioxide, to maintain stability. Cells may be injured during freezing by solution effects predominating during slow cooling, and by intracellular ice formation at rapid cooling rates. The most obvious way to avoid ice-freezing is to store the inoculum at 4°C.
