Water Activity Theory; Moisture Content; Water Activity - Decagon Devices pawkit Operator's Manual

Pawkit User Manual

3. Water Activity Theory

3. Water Activity Theory
Water is a major component of foods, pharmaceuticals, and
cosmetics. Water influences the texture, appearance, taste
and spoilage of these products. There are two basic types of
water analysis: moisture content and water activity.

Moisture Content

The meaning of the term moisture content is familiar to
most people. It implies a quantitative analysis to determine
the total amount of water present in a sample. Primary
methods for determining moisture content are loss on dry-
ing and Karl Fisher titration, but secondary methods such as
infrared and NMR are also used. Moisture content determi-
nation is essential in meeting product nutritional labeling
regulations, specifying recipes and monitoring processes.
However, moisture content alone is not a reliable indicator
for predicting microbial responses and chemical reactions in
materials. The limitations of moisture content measurement
are attributed to differences in the intensity with which
water associates with other components.

Water Activity

a
Water activity ( ) is a measurement of the energy status of
w
the water in a system. It indicates how tightly water is
bound, structurally or chemically, within a substance. Water
activity is the relative humidity of air in equilibrium with a
sample in a sealed measurement chamber. The concept of
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