Frozen drying , also known as lyophilized or cryodessication , is a low-temperature dehydration process that involves freezing the product, lowering the pressure, then removing the ice with sublimation. This is different from dehydration by most conventional methods that evaporate water using heat.
Freeze drying produces high quality products because of the low temperature used in processing. The original shape of the product is maintained and the quality of the rehydration product is very good. The main applications of frozen drying include biology (eg bacteria and yeast), biomedicine (eg surgical transplant), and food processing (eg coffee).
Video Freeze-drying
Histori
The first application of the frozen drying process is in the Andes where the Indigenous people will take lowland tubers to high altitude and let them freeze. The potato is mashed to facilitate the loss of water but when allowed to freeze at night and exposed for days, mash will lose water while the nutrients are maintained through lyophilization process. This results in a product called chuÃÆ' Â ± o which is a long shelf-life food eaten well past seasonal availability and is also kept for emergency rations, if necessary.
Frozen drying as an industrial process began in the early 1890s by Richard Altmann who devised a method to freeze dry tissue (either plant or animal), but was almost unnoticed until the 1930s. In 1909, Shackell independently created a vacuum chamber using an electric pump. However, there is no further data on documented freeze drying until Tival in 1927 and Elser in 1934 has patented a freeze-drying system with increasing freezing and condenser steps.
Significant turning points for frozen drying occurred during World War II because blood plasma and penicillin were needed to treat injuries in the field due to lack of cooling and simultaneous transport, much of a pampering serum supply before reaching the intended recipient. The freeze-drying process was developed as a commercial technique that allows blood plasma and penicillin to be chemically stable and viable without being cooled. In the 1950s-60s, frozen drying began to be seen for its multi-purpose applications for both pharmaceutical and food processing.
Initial use in food
Frozen drying products became a major commodity for astronauts and military food rations. What started for astronaut crews as tube food and freeze-dried snacks that are difficult to rehydrate, they can now enjoy warm warm food while in outer space by increasing the ease for rehydration of free dry foods with water. As technology and food processing are increasing, NASA looks for ways to provide a complete nutrition profile, reduce the crumbs and bacteria and the toxins that produce the disease. The complete nutrition profile is enhanced by the addition of algae-based vegetable oils to add polyunsaturated fatty acids. Polyunsaturated fatty acids are beneficial in mental and vision development, and as they remain stable after space travel can provide astronauts with additional benefits. The problem of crumbs is solved by adding a layer of gelatin to the food to lock and prevent crumbs. Bacteria and toxins that produce disease are reduced by quality control and development of the Critical Hazard Analysis Analysis Plan (HACCP), which is widely used today to evaluate food ingredients before, during and after processing. With this combination of three things, NASA can provide safe and healthy food for their crew while in space in a freeze-dried food source.
Military rations also come a long way from being served pork and corn that are pampered to be seasoned with mushroom sauce. How rations are selected and developed is based on acceptance, nutrition, health, production, cost and sanitation. Also, the additional requirement that the ration should have a minimum shelf life of 3 years, can be sent by air, consumption in the environment around the world, and provide a complete nutrition profile. Newly improved tray ratio (T Ration) by increasing acceptable items and providing high quality food while in the field. Frozen-frozen coffee is also included by replacing the spill-dry coffee in the fast food category.
Maps Freeze-drying
Frozen drying stage
There are four stages in the complete freeze-drying process: pretreatment, freezing, primary drying, and secondary drying.
Pretreatment
Pretreatment includes any method that treats the product before freezing. This may include product focusing, formulation revisions (ie, adding components to improve stability, maintaining appearance, and/or improving processing), lowering high-pressure steam solvents, or increasing surface area. Pieces of food are often treated with IQF to make it flow freely before freezing. In many instances, the decision to pretreat a product is based on the theoretical knowledge of freeze drying and its requirements, or demanded by cycle time or product quality considerations.
Freezing and softening
During the freezing stage, the material is cooled below its triple point, the lowest temperature at which the solid, liquid and gas phases of the material can co-exist. This ensures that sublimation rather than smelting will occur in the following steps. To facilitate faster and more efficient freeze drying, larger ice crystals are preferred. Ã, large ice crystals form a network within the product that encourages faster removal of moisture during sublimation. Ã, To produce larger crystals, the product must be frozen slowly or can spin up and down at a temperature in a process called Ã,nenealing. Frozen phase is the most important in the whole process of freeze drying, because the freezing method can affect the speed of reconstitution, the duration of the freeze-drying cycle, the stability of the product and the appropriate crystallization.
The amorphous material has no eutectic point, but they have a critical point, below the product should be maintained to prevent melting or collapse during primary and secondary drainage.
Structurally sensitive items
In the case of items in which preservation of structures is necessary, such as food or objects with living cells previously, large ice crystals will damage cell walls that can produce worse texture and loss of nutritional content. In this case, freezing is done quickly, to quickly lower the material down the eutectic point, thus avoiding the formation of large ice crystals. Typically, temperatures are frozen between -50 Â ° C and -80 Â ° C (-58 Â ° F and -112 Â ° F).
Main drain
During the primary drying phase, the pressure is lowered (to a range of several millibars), and sufficient heat is supplied to the material for ice to be sublime. The amount of heat required can be calculated by sublimation sublimation using sublimation of sublimation molecules. In this initial drying phase, about 95% of the water in the material is sublimated. This phase may be slow (it can be several days in the industry), because, if too much heat is added, the material structure can be changed.
In this phase, the pressure is controlled through the application of a partial vacuum. Vacuum accelerates sublimation, making it useful as a deliberate drying process. Furthermore, cold condenser chambers and/or condenser plates provide surface (s) for moisture to re-solidify.
It is important to note that, within this range of pressure, heat is carried mainly by conduction or radiation; the effects of convection can be neglected, due to low air density.
Secondary drying
The secondary drying phase aims to remove frozen water molecules, since ice has been removed in the primary drying phase. Part of this freeze-drying process is governed by the adsorption isotherm of the material. In this phase, the temperature is raised higher than the main drying phase, and can even be above 0 ° C, to break the physico-chemical interactions that have formed between water molecules and frozen materials. Usually pressure is also lowered at this stage to encourage desorption (usually within the range of microbars, or pascal fractions). However, there are products that benefit from increased pressure as well.
After the freeze drying process is complete, the vacuum is usually solved with an inert gas, such as nitrogen, before the material is sealed.
At the end of the operation, the final residual water content in the product is very low, about 1% to 4%.
Application freeze drying
Frozen drying causes less damage to the substance than other dehydration methods using higher temperatures. The heat-sensitive nutrient factors are lost less in the process than those that incorporate heat treatment for drying purposes. Freeze drying usually does not cause shrinkage or toughness of the material being drained. In addition, taste, odor, and nutritional content are generally 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 alcohol can produce undesirable results.
The dry-frozen product can be rehydrated (remodeled) much more quickly and easily because the process leaves microscopic pores. The pores are created by ice crystals that sublime, leaving a crack or pore in their place. This is very important when it comes to pharmaceutical use. Frozen drying can also be used to increase the shelf life of some medicines over the years.
Pharmaceuticals and biotechnology
Pharmaceutical companies often use frozen drying to increase the shelf life of products, such as live, biological, and other injectable vaccines. By removing water from the material and sealing the material in a glass bottle, the material can be easily stored, shipped, and then rearranged to its original form for injection. Another example of the pharmaceutical industry is the use of frozen drying to produce tablets or wafers, the advantage is that fewer excipients and dosage forms are quickly absorbed and easily administered.
Dry-frozen pharmaceutical products are produced as lyophilized powders for reconstitution in vials and more recently in syringes that are recharged for self-sufficiency by a patient.
Examples of lyophilized biological products include many vaccines such as Measles Live Virus Vaccine, Typhoid Vaccine, Meningococcal Polysaccharide A and C Combined Vaccine Groups. Other freeze-dried biological products include Antihemophilic Factor VIII, Interferon alfa, anti-clotting drug Streptokinase and Wasp Venom Allergenic Extract.
Many biopharmaceutical products based on therapeutic proteins such as monoclonal antibodies require lyophilization for stability. Examples of lyophilized biopharmaceuticals include blockbuster drugs such as Etanercept (Enbrel by Amgen), Infliximab (Remicade by Janssen Biotech), Rituximab and Trastuzumab (Herceptin by Genentech).
Frozen drying is also used in the manufacture of raw materials for pharmaceutical products. Active Pharmaceutical Ingredient Products (APIs) are lyophilized to achieve chemical stability under room temperature storage. Bulk Lucophilization APIs are usually done using trays instead of glass bottles.
Dry powder probiotics are often produced by mass bulk drying of living microorganisms such as Lactic acid bacteria and Bifidobacteria.
Dried food supplies
The main goal of frozen drying in the food industry is to extend the shelf life of food while maintaining quality. Frozen drying is known to produce the highest quality of food among all drying techniques because structural integrity is maintained along with the preservation of flavors. Due to costly freeze drying, it is mainly used with high value products. Examples of high-value dry-frozen products are seasonal fruits and vegetables due to the limited availability, coffee, and food used for military rations and/or pedestrians.
NASA and Military Rations
Due to its light weight per volume of dissolved food, the freeze-dried product is popular and convenient for pedestrians, as a military ration, or astronaut food. A large amount of dry food can be done compared to the same wet foods. In lieu of wet food, frozen dried foods can easily be rehydrated with water if desired and shelf life of dried products longer than fresh/wet products making it ideal for long journeys taken by pedestrians, military or astronauts. The development of frozen drying increases the variety of foods and snacks to include items such as shrimp cocktail, chicken and vegetables, butterscotch pudding, and applesauce.
Coffee
Coffee contains the flavor and aroma of quality created by Maillard's reaction during roasting and can be preserved by frozen drying. Compared to other drying methods such as room temperature drying, hot air drying and solar drying, the frozen-dried Robusta coffee beans contain more essential amino acids such as leucine, lysine, and phenylalanine. Also some non-essential amino acids that significantly contribute to the taste are maintained.
Fruits
Freeze drying can be beneficial for fruit as it can make it available throughout the year and can retain their flavor and color, making it more similar to fresh fruit than other dehydration methods. With conventional dehydration, the fruit can degrade the quality because the structure is very smooth and contains high water content. Strawberries were found to have the highest quality when frozen dry; maintaining the color, taste and ability to be re-hydrated. In addition the dried-free fruit can powder to make it more soluble and act as the base for food products, as well as being a natural source of antioxidants and dyes.
Technology industry
In chemical synthesis, the product is often frozen dry to make it more stable, or more soluble in water for later use.
In bioseparation, frozen drying can be used also as a final-stage purification procedure, as it can effectively remove solvents. Furthermore, it is able to concentrate substances of low molecular weight that are too small to be removed by the filtering membrane. Freeze drying is a relatively expensive process. The equipment is about three times more expensive than the equipment used for other separation processes, and high energy demands cause high energy costs. Furthermore, frozen drying also has a long processing time, because the addition of too much heat to the material can cause melting or structural deformation. Therefore, freeze drying is often reserved for heat-sensitive materials, such as proteins, enzymes, microorganisms, and blood plasma. The low operating temperature of the process causes minimal damage from this heat-sensitive product.
In nanotechnology, freeze drying is used for purification of nanotubes to avoid aggregation due to capillary force during ordinary thermal evaporation drying.
Other uses
Organizations such as the Document Conservation Laboratory at the National Archives and Archives of the United States (NARA) have conducted studies on frozen drying as a method of recovering damaged books and documents. While recovery is possible, the quality of recovery depends on the document material. If the document is made of various materials, which have different absorption properties, the expansion will occur at a non-uniform level, which may cause deformation. Water can also cause mold to grow or make ink bleed. In this case, frozen drying may not be an effective recovery method.
In freezing bacteriology is used to conserve special strains.
In high altitudes, low temperatures and pressures can sometimes produce natural mummies by frozen drying processes.
The advanced ceramic process sometimes uses frozen drying to make a powder that can be formed from a sprayed slurry mist. Frozen drying creates softer particles with a more homogeneous chemical composition than traditional hot spray drying, but also more expensive.
The new form of pre-freezing burial-drying bodies with liquid nitrogen has been developed by the Swedish company Promessa Organic AB, which puts it forward as an eco-friendly alternative to traditional coffins and cremation cemeteries.
The advantages of freeze drying
Freeze drying is seen as the optimal choice method for dehydration due to quality preservation, which means the characteristics of food products such as aroma, rehydration, bioactivity, noticeably higher than dry foods from other techniques.
Extension-life slide
Shelf-life extensions are the result of low processing temperatures along with rapid water transitions through sublimation. Under these processing conditions, the deterioration reaction, including nonenzymic browning, enzymatic browning, protein denaturation, is minimized. When the product is successfully dried, packaged properly, and placed in ideal storage conditions, the food has a shelf life of more than 12 months.
Rehydration
If the dry product can not be easily or completely re-hydrated, it is considered to have a lower quality. Since the final dry product is porous frozen, complete rehydration may occur in the diet. This signifies a greater product quality and makes it ideal for instant food.
Effects on nutrition and sensory quality
Due to the low processing temperatures and minimization of the deterioration reaction, nutrients are maintained and the colors are maintained. The freeze-dried fruit retains its original shape and has a distinctive texture, crisp texture.
Lack of frozen drying
Microbial Growth
Because the main method of microbial decontamination for freeze drying is the process of low temperature dehydration, the decomposing organisms and pathogens that are resistant to this condition can remain in the product. Although microbial growth is hampered by low humidity conditions, it can still survive in food products. An example of this is the hepatitis A outbreak that occurred in the United States in 2016, linked to frozen strawberries. If the product is not packaged properly and/or stored, the product can absorb moisture, allowing pathogens that were once retarded to start reproducing as well.
Cost
The frozen drying cost is about 5 times more than the conventional drying method, making it not an ideal choice if the product value does not increase after it is processed. However, costs also vary depending on the product, packaging materials, processing capacity, etc. Also, the highest energy costs for sublimation are compared to freezing, vacuum and condensation steps.
Silicon Oil Leakage
Silicone oil is a common fluid used to heat or cool racks in a freeze-dryer. A sustained heat/cold cycle can cause leakage in silicone oil in weak areas that connect shelves and hoses. This can contaminate products that cause major losses to food products. Therefore, to avoid this problem, the mass spectrometer is used to identify steam released by silicone oil to take immediate corrective action and prevent product contamination.
Frozen dryer equipment and type
There are many types of freeze-dryers available, however, they usually contain several important components. These are vacuum chambers, racks, condenser processes, rack-fluid systems, cooling systems, vacuum systems and control systems.
Important component functions
Chamber
This space is very smooth and contains insulation, internally. It is made with stainless steel and contains several shelves to hold the product. Hydraulic or electric motors are installed to ensure air-tight doors when closed.
Condenser process
The condenser process consists of a coil or a cooling plate which can be external or internal to the chamber. During the drying process, the condenser traps water. To improve efficiency, condenser temperatures must be 20 Â ° C less than the product during primary drying and have a liquefying mechanism to ensure that the maximum amount of water vapor in the air is condensed.
Shelf fluid
The amount of heat energy required during the primary and secondary drying phases is governed by an external heat exchanger. Normally, silicone oil is circulated around the system with the pump.
Cooling system
This system serves to cool the rack and condenser process by using a liquid compressor or nitrogen, which will supply the energy needed to freeze the product.
Vacuum system
During the drying process, a vacuum of 50-100 microbones is applied, by a vacuum system, to remove the solvent. A two-level rotary vacuum pump is used, however, if it is a large space then it needs some pumps. This system compresses the gas that can not be condensed through the condenser.
System control
Finally, the control system regulates controlled values ​​for shelf temperature, pressure and time dependent on the product and/or process. The frozen dryer may last for several hours or days depending on the product.
Contact Freeze Dryers
Contact the frozen dryer using food contact (conduction) with heating elements to supply sublimation energy. This type of frozen dryer is a simple basic model to prepare for sample analysis. One of the main ways of contacting frozen dryer heat is with platforms like shelves that contact samples. Shelves play a major role because they behave like a heat exchanger at different times from the freeze-drying process. They are connected to a silicon oil system that will dissipate heat energy during freezing and provide energy during drying time.
In addition, the rack-fluid system works to provide a specific temperature to the rack during drying by pumping liquids (usually silicone oil) at low pressure. The disadvantage of this type of freeze dryer is that heat is simply transferred from the heating element to the sample side which directly touches the heater. This problem can be minimized by maximizing the surface area of ​​the sample that touches the heating element by using a striped tray, slightly compressing the sample between two solid heat plates above and below, or compressing with hot mesh from the top and bottom.
Radiant Freezer
The radiation freeze dryer uses infrared radiation to heat the sample in the tray. This type of heating allows a simple flat tray to use as an infrared source can be placed on top of a flat tray to radiate down into the product. Infrared radiation heating allows very uniform heating of the product surface, but has a very small capacity for penetration so it is used mainly with very shallow trays and homogeneous sample matrices.
Microwave-freeze frozen dryer
The freeze of microwave freezer utilizes microwaves to allow deeper penetration into the sample to speed up the sublimation process and warm up in freeze drying. This method can be very complicated to set and run because microwaves can create an electric field capable of causing the gas in the sample space to be plasma. This plasma has the potential to burn the sample, so maintaining the appropriate microwave power for the vacuum level is a must. The level of sublimation in a product may affect the microwave impedance, in which the power of the microwave must be altered properly.
See also
- Freeze-dried and NASA food
- List of dried foods
- Supercritical drying
References
External links
- FDA Guide for Lyophilization of Parenterals Examination
Source of the article : Wikipedia
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