Freeze drying or lyophilization is a drying process, in which the solvent and /or the medium of suspension is crystallized at low temperature and thereafter sublimated from the solid state directly into the vapor phase.
The term lyophilization is means to ‘make solvent loving’. Freeze drying is mostly done with water as solvent.
The process reduces the moisture levels of the biological material from 80% to about 1-4% by the process known s sublimation.
It helps the product to keep for long period of time without the degradation affect of either microbial or autolytic enzymes.
Most freeze drying is done by batch processes because of the requirements for operation at reduced pressure.
The freeze drying process include elements of:
*Heat flow to the specimen
*Drying boundary temperature
*Vapor flow through the dried shell
*Chamber design
*Absolute pressure
*Condenser temperature
All the elements are interdependent and no one element can be modified without affecting the others.
During the freeze drying process, the freezing steps is one of the most important steps because it fixes the structure and the morphology of the frozen material and consequently it determines the final morphology of the material and thus is rehydration properties and its stability.
Process of freeze drying
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