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Measurement of Water Activity in Foods: A Review
1Department of Microbiology, University of the Orange Free State, P.O. Box 339, Bloemfontein 9300, South Africa.
Journal of Food Protection
|March 1, 2019
Summary
This review examines methods for measuring water activity in foods, based on colligative properties. Specialized apparatus offers faster, wider-range measurements with good accuracy, while simple methods like water sorption isotherms are precise but slower.
Area of Science:
- Food Science
- Analytical Chemistry
Background:
- Water activity is a critical factor in food stability and safety.
- Numerous methods exist to measure water activity, utilizing colligative properties of solutions.
Purpose of the Study:
- To review and categorize methods for measuring water activity in foods.
- To compare the precision, accuracy, and limitations of different measurement techniques.
Main Methods:
- Review of literature on food water activity measurement techniques.
- Categorization of methods based on apparatus complexity (simple vs. specialized).
- Analysis of methods based on freezing point depression and equilibrium relative humidity.
Main Results:
- Water sorption isotherm method offers best precision/accuracy among simple apparatus methods but has limitations.
- Specialized apparatus methods (electric hygrometer, dew point hygrometer, vapor pressure manometer) provide faster results over a wider range.
- Some methods are unsuitable for foods with volatiles or high microbial loads.
Conclusions:
- Method selection depends on required precision, speed, sample type, and available equipment.
- Specialized instruments are generally superior for rapid and broad-range water activity determination in foods.
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