5. Preservation by dehydration

5.1 Principle

The preservation of cells over long periods by dehydration implies high and extreme levels of dehydration (water activity level between 0.2 and 0.1). Indeed, when water concentration is not sufficiently low, certain cellular enzymes are still active and can participate in cell degradation. Enzymes such as proteases and oxidases operate down to water activities of 0.45.

This level of dehydration is not sufficient, however, as non-enzymatic oxidation and Maillard reactions can still occur at this level. It is therefore necessary to dehydrate the cells to levels that lead to the formation of a highly viscous amorphous state known as the "glassy state" (figure