Lyophilization is used in the drying of foods and the preservation of archival materials (ie books and documents), but mainly in the pharmaceutical and biotechnological research and industrial-scale production of cosmetic products or medicaments such as tablets.
The process goes through three separate steps, three interdependent processes – freezing, primary drying(sublimation), and secondary drying (desorption).
Freezing – in this step, the moist material is frozen below the temperature at which it cannot exist in the liquid state. This will ensure that there is no melting instead of sublimation.
Primary drying – during this phase, the air pressure in the freezer is reduced to several hundred Pascal. Then, heat is delivered (mainly by conduction and radiation) so that water can sublime. Thus, approx. 95% of the water is removed from the material.
Secondary drying – this stage is approached only in cases where it is needed to be even more dry state. During this phase, the remaining non-frozen water molecules are removed, which are held on the surface of the solids by adsorption. After the second drying, about 1 to 5% of water remains in the material.
PHARMACEUTICAL / BIOLOGICAL LYOPHILIZATION
LABORATORY FREEZE DRYING
During lyophilization, it is not necessary to use any risk preservatives or flavor enhancers. In this procedure, the food is first frozen rapidly. When sublimating the water crystals in food, they pass into the gaseous state in the form of water vapor. The meal retains the original texture and flavor.
According to recent research, freeze-dried foods store more vitamins and minerals than traditional hot air drying.