RESUMEN
Several important practical steps are recognized in the process of freeze-drying of biologic material. The first of these is the selection of conditions optimal for the stability of the substance at the normal storage temperature, usually +5 degrees C. The second step involves the collection of material, storage at some choice freezing temperature (preferably around -20 degrees C) until use. The third step consists of the freeze-drying process itself, with preliminary freezing at another temperature, usually between -60 degrees and -80 degrees C. How these steps affect the quality of biologic products, proteins and polysaccharides has been the subject of study in our laboratories. The results have led us to the conclusion that molecular rearrangements occur at certain critical frozen temperatures which, in combination with time, leads to inactivation in some cases, stability in others. Such critical temperatures can be measured for other products and systems.