What is water activity?
Water activity defines the energy status of water in a substance or a system. It describes the amount of water available for hydration of materials.Water Activity is measured in Aw units in the scale from 0 to 1, When Aw – 1, all of the water is available for hydration (as in distilled water), When Aw – 0, there is no water available at all.The determination of Water activity is important in the production process and in the quality assurance process. First, it influences the product chemical, enzymatic and microbiological stability. Second, it influences the protein and vitamin content, shelf life, storage, packaging, solubility, texture, color, taste and nutritional value.While PH, temperature and some other factor will determine how fast the bacteria will grow, water activity may be the most important factor in controlling spoilage. Most bacteria, for example, do not grow at water activities below 0.91, and most molds cease to grow at water activities below 0.80.
By measuring water activity, it is possible to predict which microorganisms will and will not be potential sources of spoilage, as seen in the following table:
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