Effect of Varying Residual Moisture Content on the Viability of Lyophilized Algae

Abstract

IT has long been recognized that the ability of cells to resist heat, cold, and desiccation is somehow related to the degree of hydration of the protoplasm. Active protoplasm in normal vegetative cells is usually composed of about 90 per cent water by weight¹. Specialized reproductive structures such as spores and seeds, which show increased hardiness in regard to heat or desiccation, may consist of only 5–10 per cent water by weight². It is important, however, to consider not only the total water content of biological material but also the water activity. Water molecules which are attracted and held by ions, polar molecules and hydrophilic colloids are spoken of collec tively as bound water. This water, which will not freeze regardless of how low the temperature is taken, shows greatly reduced activity and is generally assumed to be incapable of acting as a solvent³. There is no clear-cut distinction between such bound water and free water; one can only differentiate them by definition or by reference to results of specific analytical procedures. This bound water is considered by some investigators to be important in the spatial configuration of macromolecules and, during dehydrating conditions, to protect the cellular proteins from denaturation^4,5.