Freeze Drying Usage Areas
Freeze drying is less damaging to the material than other dehydration methods that use higher temperatures. Heat sensitive nutrient factors are lost less in the process than in processes with heat treatment for drying purposes. Freeze drying generally does not cause shrinkage or hardening of the material being dried. Additionally, flavors, fragrances, and nutritional content often remain unchanged, making the process popular for food preservation. However, water is not the only chemical capable of sublimation, and the loss of other volatile compounds such as acetic acid (vinegar) and alcohols can have undesirable consequences.
Freeze-dried products can be rehydrated (reconstituted) much more quickly and easily as the process leaves microscopic pores. Pores are formed by ice crystals that sublimate, leaving voids or pores in their place. This is especially important when it comes to pharmaceutical uses. Freeze drying can also be used to extend the shelf life of some drugs for many years.
Freeze Drying of Food
The primary purpose of freeze drying in the food industry is to extend the shelf life of food while maintaining its quality. Freeze drying is known to result in the highest food quality of all drying techniques. Because structural integrity is preserved along with the preservation of aromas. Since freeze drying is expensive, it is mainly used for high value products. Examples of high-value freeze-dried products are seasonal fruits and vegetables due to their limited availability, coffee and military rations, food for astronauts, cosmonauts or hikers.
Fruits
With conventional dehydration, the quality of the fruit may deteriorate, as their structure is very delicate and contains a high level of moisture. Strawberries were found to be of the highest quality when freeze-dried; retains color, flavor and ability to rehydrate.
Pharmaceuticals and Biotechnology
Freeze-drying is often used to increase the shelf life of products such as biologics and other injectables. By removing water from the material and capping the material in a glass bottle, the material can be easily stored, transported and then reconstituted to its original form for injection. Another example from the pharmaceutical industry is freeze drying is used to produce tablets or wafers, the advantage of which is less excipients and also a dosage form that is quickly absorbed and easily administered.
Freeze-dried pharmaceutical products are produced as lyophilized powders for reconstitution in bottles and more recently in prefilled syringes for self-administration by a patient.
Examples of lyophilized biological products include many vaccines such as live measles virus vaccine, typhoid vaccine, and combined meningococcal polysaccharide vaccine groups A and C. Other freeze-dried biologics include antihemophilic factor VIII, interferon alpha, the anti-blood clot drug streptokinase, and wasp venom allergenic extract.
Cell extracts that support cell-free biotechnology applications such as point-of-care diagnostics and biomanufacturing are also freeze-dried to increase stability under room temperature storage.
Dry powders of probiotics are usually produced by freeze-drying live microorganisms such as lactic acid bacteria and bifidobacteria in bulk.
Coffee
Coffee contains flavor and aroma qualities due to the Maillard reaction during roasting and can be preserved by freeze drying. Compared to other drying methods such as room temperature drying, hot air drying and sun drying, freeze-dried Robusta coffee beans contain higher amounts of essential amino acids such as leucine, lysine and phenylalanine. It retains several non-essential amino acids that contribute significantly to flavor.
insects
Freeze drying is widely used to preserve insects for consumption. All of the freeze-dried insects are sold as exotic pet food, bird food, fish food, and increasingly for human consumption. Powdered freeze-dried insects are used as a protein base in animal feed and as a nutritional supplement for human use in some markets. Farm-raised insects are used for all the above-mentioned purposes against collecting wild insects, except in the case of grasshoppers, which are usually harvested from field crops.
Technology Industry
In chemical synthesis, products are freeze-dried to make them more stable or more easily dissolved in water for subsequent use.
In bioseparations, freeze drying can also be used as a late stage purification procedure as it can effectively remove solvents. It also has the ability to concentrate substances with molecular weights too small to be removed by a filtration membrane.
Freeze drying is a relatively expensive process. The equipment is about three times more expensive than equipment used for other separation processes, and high energy demands lead to high energy costs. Freeze drying also has a long processing time because adding too much heat to the material can cause melting or structural deformations. Therefore, freeze drying is generally reserved for heat sensitive materials such as proteins, enzymes. Microorganisms and blood plasma, the low operating temperature of the process causes minimal damage to these heat sensitive products.
In nanotechnology, freeze drying is used for nanotube purification to prevent aggregation caused by capillary forces during normal thermal evaporation drying.
NASA and Military Supplies
Because of its light weight per volume of reconstituted food, freeze-dried products are popular and suitable for hikers as military rations or astronaut meals. A larger amount of dried food can be transported compared to the same weight of wet food. Freeze-dried food instead of wet food can be easily rehydrated with water if desired, and the dried product has a longer shelf life than fresh or wet food, making it ideal for long journeys by hikers, military personnel or astronauts.
