Lyophilization/freeze drying is a method of extracting the water from Biological samples,foods and other products so that foods or products remain stable and are easier to store at room temperature. Biological materials should be dried to stabilize them for storage, preservation and shipping. In many cases this drying can cause damage and some loss of cellular or protein activity. Lyophilization significantly reduces damage to biological samples.
Process of Lyophilization
The process of lyophilization requires sterile conditions and special equipment.
First a sample is frozen, and then the pressure of the surrounding environment is reduced. This reduction in pressure allows the water to sublimate: the direct transformation of a substance from solid to gas phase, without the application of heat. A variety of industries use lyophilization for long-term storage and shipping of samples because it helps with sample stability and purity. Despite the involved process, pharmaceutical, biotechnology, agricultural, and many high-tech industries employ lyophilization as a standard practice because heat can adversely affect samples.
Advantages of Lyophilization
Products go through freeze drying process, will have great advantages compare other drying method even its original type, Think about freeze dried products packages no need refrigeration, only 3% to 10% weight but nutritional or ingredients contain same with original, shelf life up to 20 years, could quick rehydration by add water or solvent if need. So whether in pharmaceutical, food, chemical, fruit, milk, pet food area, freeze drying machines are popular.
1, Structure, Texture, Appearance
The freezing stage form and decide dried products shape.
Frozen products drying in low temperature, water inside (solid phase) removed by sublimation/vapor(ice absorb energy and turn to gas, skip water phase), raw material drying from surface layer till to bottom layer.By this, will not damage their physical structure, texture, no shrink.
Its very different with other drying method principle of water boiling which drying from bottom part to surface part, that dried products will bulge light or heavy as per temperature set, dried products have shrink and taste like leather.
2, Nutrition, taste, color
Freeze dried products tend to retain most of their nutritional quality, taste etc. this is also because the low temperature drying avoid damage to heat sensitive products such as enzymes, flavours, proteins and vitamins.
We could understand the differences between freeze dried products and original form is water.
3, Drying Pre-treatment
Except high sugar or high fat products need special treatment (for example: honey). Most freeze drying process or raw material no need special treatment, because freezing drying itself is a kind of concentration, no need additives to increase the taste.
4, Transport and storage
Freeze drying process could control dried products moisture to 2%,you also could adjust by drying time. Very light weight compare fresh form, easy handle and transport, After proper packing, they could transport and storage in room temperature without any critical requirement.
Equipment used for Lyophilization –Lyophilizer
A lyophilizer consists of
- A vacuum chamber containing product shelves which are capable of cooling and heating containers and their contents.
- A vacuum pump, a refrigeration unit, which is associated controls are connected to the vacuum chamber.
Samples are generally placed in containers such as glass vials that are placed on the shelves within the vacuum chamber.
Cooling elements within the shelves freeze the product. Once the product is frozen, the vacuum pump evacuates the chamber and the product is heated. Heat is transferred by thermal conduction from the shelf, through the vial, and ultimately into the product.
Comparison with Liquid-Phase drying
Lyophilization avoid denaturation that is caused by heating the product, by maintaining it frozen throughout drying. This is the most obvious advantage over liquid-phase drying which cause the denaturation of proteins and other products.
Equally important is that in liquid-phase drying there is an undesirable shrinkage and concentration of active constituents that causes damage as well as a movement of these constituents to the surface of evaporation, where they form a dense, impermeable skin that inhibits drying, and later, rehydration. Such effects can be avoided by spray drying, but this requires brief exposure to temperatures around 100 degree C.