What is a freeze dryer?

The lyophilizer is the apparatus used to carry out lyophilization. It consists of the following parts: dry chamber or lyophilization chamber: it is the place where the substance to be lyophilized is placed, condenser with a refrigeration circuit: it communicates with the dry chamber and it is where the vapor that is produced in the sublimation is condensed and finally a vacuum system.

What is lyophilization?

Lyophilization is a process that aims to separate water (or another solvent) from a solution by freezing and subsequent sublimation of the ice under reduced pressure. Freeze drying is the gentlest process for drying products and is the best method for drying organic or inorganic compounds without altering their qualitative or quantitative composition. The lyophilization process is carried out under vacuum and at low temperature and thus, for example, it is possible to avoid denaturation of proteins. Food and biological materials such as cells, tissues, bacteria and vaccines become dry products, avoiding their passage through their liquid phase, and consequently enzymatic, biological and chemical changes.

Advantages of lyophilization over other techniques

  • Products are obtained that can be regenerated very quickly.
  • The shape and characteristics of the final product are essentially the original ones.
  • It is an ideal process for drying thermolabile substances.
  • Oxidizable constituents are protected.
  • The final moisture content is very low.

Stages of lyophilization

At the laboratory level, round bottom vials, tubes or flasks are used for small amounts of sample (greater resistance, with the possibility of closure within the lyophilizer). At an industrial level, trays are used for large quantities of material to be lyophilized. The procedure for lyophilizing the sample consists of several stages:

Freezing the sample at low temperatures

In freeze-drying, the freezing of the products is an important stage since it directly influences the appearance and quality of the final product. The sample is usually placed in liquid nitrogen (-196ยบC) or in a dry ice and acetone bath (-78ยบC) until it freezes completely. Frozen products must have an opaque appearance and maintain it throughout the drying process.

Drying of the frozen product by sublimation

The frozen sample is placed in one of the containers in the sublimation chamber and the vacuum is carefully applied. If there are other products that are being lyophilized in other containers connected to the chamber, we will have to close the keys of each one of them, open ours, and when it has reached the vacuum, open all the others.

Once the lyophilization is finished, the reverse process must be carried out to break the vacuum of our sample very carefully, allowing air to enter slowly. Otherwise, turbulence can be created causing the solid sample to exit the vial and become dispersed on the chamber walls. The tap is then closed, disconnected from the chamber, the vial is removed and capped to prevent the entry of moisture.

Product storage

Properly sealed and lyophilized products can be stored for long periods of time with the retention of the physical, chemical, biological and organoleptic properties of their original states.

Lyophilization reduces quality losses caused by chemical reactions, enzymatic and non-enzymatic degradation. Oxidation processes can be controlled by storing lyophilized products in oxygen-impermeable containers. Storing lyophilized products in places with low temperatures avoids protein denaturation.

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