Freezing and freeze-drying

Abstract

Freezing of biological materials is commonly carried out to delay biochemical and chemical changes resulting in loss of activity. However, the physicochemical background of freezing is not well understood. Freeze-drying is generally aimed at preserving biological materials and bioactive components for long periods of time without the need for frozen storage. Freeze-drying relies on proper freezing and process control based on an understanding of the frozen state properties of biological materials. Such properties relate to unfrozen water and its distribution across carbohydrates, proteins and other components. Here, novel methods for deriving accurate protein hydration levels and unfrozen water content are discussed. The role of water and carbohydrate distribution in preserving the viability of micro-organisms in freezing and freeze-drying is also discussed, as this is a significant factor affecting the success of freezing and freeze-drying processes in the production of starter cultures and the preservation of probiotic bacteria.