Lyophilization, also known as freeze-drying, is a process used for preserving biological material by removing the water from the sample, which involves first freezing the sample and then drying it, under a vacuum, at very low temperatures. Lyophilized samples may be stored much longer than untreated samples.
Components of a 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.
Advantages of the Lyophilization
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.
