Water Activity Control Using Pairs of Salt Hydrates

3 Water Activity Control Using Pairs of Salt Hydrates 

An alternative method for water activity control is based on the fact that salt hydrates containing different numbers of water molecules are interconverted at fixed water activities [15]. The first salt hydrate used was Na2C03- 10H2O. This is converted to Na2C03-7H20 at a water activity of 0.74 at 24 °C. The salt hydrates act as a buffer of the water activity. As long as both salt hydrates are present, the water activity remains at 0.74. If another water activity is desired, another pair of salt hydrates should be chosen. The salt hydrates can be added directly to the organic reaction mixture. One should be careful that the salt hydrates do not interfere with the enzyme or the enzymatic reaction. 

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