ABSTRACT
Among existing dehydration methods, freeze-drying is well known to produce highquality (with respect to organoleptic and nutritional criteria) food products. It also has unique benefits for stabilization and preservation of biological activity of pharmaceutical products. Freeze-drying is restricted in food industries to high
added-value products such as coffee, ingredients (fruits, vegetables, aromatics herbs, etc.), and starter cultures (direct inoculation with lactic acid bacteria), whereas its main field of application is pharmaceutical protein stabilization. The freeze-dried product has a very high and rapid hydration capacity and structure, appearance and product activity are preserved for a long time (several months to several years) at temperatures close to room temperature. However, freeze-drying, as a batch process, remains an expensive and time-consuming process. Freeze-drying is based on three main mechanisms: freezing to crystallize majority of water content of the product, sublimation of the solid water, usually associated to primary drying, and desorption of unfreezable residual water during the secondary drying to achieve a stable dried state. Referring to a schematic representation of the freeze-drying equipment (Figure 20.1), energy consumption is mainly due to sublimation step, vacuum (pressure below 100 Pa), and condensation for vapor recovery (cold trap temperature below 508C).
