Freeze-dried products can be rehydrated (reconstituted) much more quickly and easily because the process leaves microscopic pores. The pores are created by the ice crystals that sublimate, leaving gaps or pores in their place. This is especially important when it comes to pharmaceutical uses. Freeze-drying can also be used to increase the shelf life of some pharmaceuticals for many years.
Pharmaceuticals and biotechnology
Pharmaceutical companies use freeze-drying to increase the shelf life of some products, such as live virus vaccines,[19] biologics,[20] and other injectables. By removing the water from the material and sealing the material in a glass vial, the material can be easily stored, shipped, and later reconstituted to its original form for injection. Another example from the pharmaceutical industry is the use of freeze drying to produce tablets or wafers, the advantage of which is less excipient as well as a rapidly absorbed and easily administered dosage form.
Freeze-dried pharmaceutical products are produced as lyophilized powders for reconstitution in vials, and more recently in prefilled syringes for self-administration by a person.
Examples of lyophilized pharmaceutical drugs include:
- Vancomycin, an intravenous antibiotic for treatment of complicated skin infections, bloodstream infections, endocarditis, bone and joint infections, and meningitis.[21]
- Activase, an intravenous "blood clot buster" used for treatment of ischemic stroke.[22]
- Carmustine, a chemotherapy drug used for treatment of glioblastoma, brainstem glioma, and other brain tumors.[23]
Biological products
Examples of lyophilized biological products include:
Lyophilized biologics can be pressed into pellets and tablets for anhydrous and high-density, solid-state storage of biological products.[27]
In bioseparations, freeze-drying can be used also as a late-stage purification procedure, because it can effectively remove solvents. Furthermore, it is capable of concentrating substances with low molecular weights that are too small to be removed by a filtration membrane. Freeze-drying is a relatively expensive process. The equipment is about three times as expensive as the equipment used for other separation processes, and the high energy demands lead to high energy costs. Furthermore, freeze-drying also has a long process time, because the addition of too much heat to the material can cause melting or structural deformations. Therefore, freeze-drying is often reserved for materials that are heat-sensitive, such as proteins, enzymes, microorganisms, and blood plasma. The low operating temperature of the process leads to minimal damage of these heat-sensitive products.
- Many vaccines such as live measles virus vaccine, typhoid vaccine, and meningococcal polysaccharide vaccine groups A and C combined.
- Therapeutic proteins including antihemophilic factor VIII
Live material
Some live cell cultures can be freeze-dried, stored for an extended period, and then reconstituted into a live, functional state. An excipient, more specifically a cryoprotectant, may be required.[28]
Even if the cell is damaged beyond resuscitation, it is preserved.[31] This can be helpful for later research too: although the type strain culture for Vampirovibrio chlorellavorus could not been resuscitated, it contained enough DNA for its genome to be sequenced.[32]
- Prokaryotes and yeast are relatively easy to freeze-dry and then resuscitate.[28]
- In bacteriology freeze-drying is used to conserve special strains.
- Dry powders of
Technological industry
In chemical synthesis, products are often freeze-dried to make them more stable, or easier to dissolve in water for subsequent use.
In nanotechnology, freeze-drying is used for nanotube purification to avoid aggregation due to capillary forces during regular thermal vaporization drying.
Food
The primary purpose of freeze drying within the food industry is to extend the shelf-life of the food while maintaining the quality.[1] Freeze-drying is known to result in the highest quality of solid foods of all drying techniques because structural integrity is maintained along with preservation of flavors.[1] Because freeze drying is expensive, it is used mainly with high-value products.[4] Examples of high-value freeze-dried products are seasonal fruits and vegetables because of their limited availability, and foods used for military rations, astronauts/cosmonauts, and/or hikers.[4]
Water-based drinks such as coffee and tea are also freeze-dried. Compared to heat-based drying, freeze-drying preserves more volatile aroma compounds.[2] Freeze-drying is also used to make instant soup bricks.[33]
NASA and military rations
Because of its light weight per volume of reconstituted food, freeze-dried products are popular and convenient for hikers, as military rations, or astronaut meals.[1] A greater amount of dried food can be carried compared to the same weight of wet food. In replacement of wet food, freeze dried food can easily be rehydrated with water if desired and shelf-life of the dried product is longer than fresh/wet product making it ideal for long trips taken by hikers, military personnel, or astronauts. The development of freeze drying increased meal and snack variety to include items like shrimp cocktail, chicken and vegetables, butterscotch pudding, and apple sauce.[13]
Coffee
Coffee contains flavor and aroma qualities that are created due to the Maillard reaction during roasting.[35] An instant coffee can be produced by freeze-drying a water extract of roasted beans.[2] Compared to other drying methods like room temperature drying, hot-air drying, and solar drying, Robusta coffee beans that were freeze-dried contained higher amounts of essential amino acids like leucine, lysine, and phenylalanine.[35] Also, a few non-essential amino acids that significantly contributed to taste were preserved.[35]
Fruits
With conventional dehydration, berries can degrade in quality as their structure is delicate and contains high levels of moisture. Strawberries were found to have the highest quality when freeze dried; retaining color, flavor, and ability to be re-hydrated.[36]
Insects
Freeze-drying is used extensively to preserve insects for the purposes of consumption. Whole freeze-dried insects are sold as exotic pet food, bird feed, fish bait, and increasingly for human consumption.[37][38] Powdered freeze-dried insects are used as a protein base in animal feeds, and in some markets, as a nutritional supplement for human use.[38][37] Farmed insects are generally used for all of the aforementioned purposes versus harvesting wild insects, except in the case of grasshoppers which are often harvested out of field crops.[37]
Taxidermy
Freeze-drying is among the methods used to preserve animals in the field of taxidermy. When animals are preserved in this manner they are called "freeze-dried taxidermy" or "freeze-dried mounts". Freeze-drying is commonly used to preserve crustaceans, fish, amphibians, reptiles, insects, and smaller mammals.[39] Freeze-drying is also used as a means to memorialize pets after death. Rather than opting for a traditional skin mount when choosing to preserve their pet via taxidermy, many owners opt for freeze-drying because it is less invasive upon the pet's body.[40]
Other uses
Organizations such as the Document Conservation Laboratory at the United States National Archives and Records Administration (NARA) have done studies on freeze-drying as a recovery method of water-damaged books and documents.[41] While recovery is possible, restoration quality depends on the material of the documents. If a document is made of a variety of materials, which have different absorption properties, expansion will occur at a non-uniform rate, which could lead to deformations. Water can also cause mold to grow or make inks bleed. In these cases, freeze-drying may not be an effective restoration method.
Advanced ceramics processes sometimes use freeze-drying to create a formable powder from a sprayed slurry mist. Freeze-drying creates softer particles with a more homogeneous chemical composition than traditional hot spray drying, but it is also more expensive.
