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Introduction to Freeze Drying 3: Why Freeze Dry? As a method of preservation, freezing alone has three major disadvantages: the high cost of maintaining frozen stocks, the problems associated with transportation of frozen materials, and the potential risk of total loss of the product in the event of a freezing plant failure. Conventional drying methods traditionally used high temperatures but this causes physical and/or chemical changes to the product. For bio-products such as enzymes and hormones this means a reduction in biological activity, and for foodstuffs this means changes in sensory qualities. With freeze-drying, heat-sensitive drugs and biologicals can be dried at low temperatures. The avoidance of high temperatures helps to reduce the extent of decomposition or loss of activity in biological products, and also circumvents the alteration of taste and sensory qualities in foods. Freeze-dried products have a very high surface area, which enables them to be reconstituted quickly and easily with the re-introduction of the solvent (usually water). This is particularly valuable in the case of emergency vaccines and antibodies, which need to be solubilised and administered as quickly as possible. Foods benefit from being freeze dried as their sensory qualities such as colour, size, smell and taste are only minimally affected in comparison to other drying processes. Freeze drying is also more compatible with the production of particle-low pharmaceuticals, in comparison to dry powder filling. Solutions can be sterile filtered immediately before being transferred to vials and freeze-dried. In short, freeze-drying offers a range of advantages to alternative methods in addition to simple stabilisation.
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