Lyophilization, also known as freeze-drying or cryo-desiccation, is the process by which water is removed from a sample without the need to apply heat. Many labs prefer the process of lyophilization over direct heat when it comes to long-term sample storage since freeze-drying prevents sample contamination and promotes sample stability in life science and food manufacturing applications.
Benefits of lyophilization (freeze-drying):
Lyophilization has many advantages over the other drying and preserving techniques.
- It maintains food/ biochemical and chemical reagent quality because they remains at a temperature that is below the freezing-point during the process of sublimation.The use of lyophilization is particularly important when processing lactic bacteria, because these products are easily affected by heat.
- Food/biochemicals and chemical reagents which are lyophilized can usually be stored without refrigeration, which results in a significant reduction of storage and transportation costs.
- Lyophilization greatly reduces weight, and this makes the products easier to transport. For example, many foods contain as much as 90% water. These foods are 10 times lighter after lyophilization.
- Because they are porous, most freeze-dried products can be easily rehydrated. Lyophilization does not significantly reduce volume, therefore water quickly regains its place in the molecular structure of the food/ biochemicals and chemical reagents.
- Mammalian cells can not be preserved by lyophilization because it can desteoy mammalian cells. Many microorganisms and proteins survive lyophilization well,because they rehydrate easily and quickly because of the porous structure left after the ice sublimes.
- Wear appropriate eye protection at all times when working with or near a lyophilizer.
- Specimens shell-frozen in ampoules are dried on a vacuum manifold or in a chamber-type drier at low negative pressure. If the glass neck of the ampoule is sealed off while the ampoule is still under vacuum, it may cause implosion, either during the sealing or later when the evacuated ampoule is being opened. To avoid this, after drying is completed, and before sealing is done, bring the pressure within the ampoule back to normal by gradually introducing dry nitrogen, avoiding turbulent disturbance of the dry product.
- The narrow or constricted neck of the ampoule is contaminated if the specimen is allowed to run down the wall of the neck during filling. Subsequently, when the ampoule is sealed with a torch, the dried material on the wall becomes charred or partially decomposed; residues of this material may adversely affect the dried material when it is reconstituted. To avoid this, a syringe with a long cannula or a Pasteur-type pipette should be used to fill the vial. Do not allow the delivery end of the cannula or pipette to touch the neck of the vial.
- All ampoules used for freeze-drying of cultures, toxins, or other biohazardous material should be fabricated of Pyrex-type glass. This type of glass requires a high-temperature torch using an air-gas or oxygen-gas mixture for sealing. These hard glass ampoules are much less apt to form gas bubbles that burst inwardly during sealing under vacuum than the soft glass ampoules and are more resistant to breakage during handling and storage.
- The filling of ampoules and vials with infectious specimens, the subsequent freeze-drying, and sealing or closing of ampoules and vials in the preparation of dry infectious specimens should be performed in a biological safety cabinet. The same is true for the preparation of ampoules and vials containing liquid specimens not subject to freeze-drying.
How Heat Affects Long-Term Storage of Samples
Biotechnology and pharmaceutical industries frequently deal with highly labile materials. Using heat to dehydrate samples that are in constant flux can have drastic consequences on sample stability and quality. For example, the pharmaceutical industry often uses compounds such as antibodies and biologics for therapeutic treatments. These compounds are comprised of proteins with rigidly defined macromolecular structures. Any alteration in these structures can either decrease or abolish the function of the protein in vivo. Application of heat easily breaks non-covalent bonds and interactions that are responsible for holding these molecules in their precise shape, rendering the samples useless.
Dehydration by heat also has adverse effects in the food and agricultural industry. Some chemical components are extremely volatile, while others are stable at high temperatures. Using heat for dehydration can cause the loss of some chemicals. Thus, the resulting compound will be something entirely different than the starting material. In these industries, lyophilization is used for long-term storage of samples to preserve chemical composition and taste.
How Water Affects Long-Term Storage of Samples
Water possesses some very dynamic chemical properties. Two of the most salient properties are its ability to be a powerful solvent, and its change in chemical structure when frozen. Unfortunately, this makes water a poor choice for long-term storage of bio-macromolecules. Over long periods of time, water can be used to break many of the most common forms of covalent bonds found in these molecules. When water freezes, the nature of the solid structure is vastly different from that of the liquid, which can cause molecules to precipitate (i.e. become insoluble).
Lyophilization is the Best Solution
Given the adverse effects of heat and water on long-term storage of sample, lyophilization is often the best solution. Besides increasing sample shelf life, freeze-drying samples also reduces sample weight and volume, which can cut down on storage and shipping costs. Lyophilization can also remove the need to ship samples on dry ice, as the samples are more stable at room temperature. From sample stability and purity to increased shelf life and reduced costs, lyophilization is a convenient, safe and efficient method for long-term storage of lab samples.