Water Activity (Aw) in Food Science

Questions and Answers

Caking

It increases

Around 0.3 aw

0.60-0.70 aw Signup and view all the answers

By dehydrating the product, using edible films and coatings, and additives involved in water binding Signup and view all the answers

They are involved in water binding Signup and view all the answers

Water activity affects microbial growth Signup and view all the answers

It determines the texture Signup and view all the answers

Maillard Browning, Lipid Oxidation, Hydrolysis, Nutrient Degradation, and Enzymatic Reactions Signup and view all the answers

To prevent mold growth Signup and view all the answers

Study Notes

Water content alone is not a reliable indicator of perishability.
Aw is a measure of the intensity of water associated with non-aqueous constituents.
Bound water is less able to support degradative activities like microbial growth or hydrolytic chemical reactions.

Aw is an equilibrium property of water at a given temperature and moisture content.
Aw = p/po, where p is the partial pressure of water vapor at the surface of the product, and po is the saturation pressure or the partial pressure of water vapor above pure water at the same temperature.
Aw = RVP (relative vapor pressure) = ERH/100, where ERH is the equilibrium relative humidity.

Water activity is temperature-dependent.
Temperature changes water activity due to changes in water binding, dissociation of water, solubility of solutes in water, or the state of the matrix.
The effect of temperature on water activity is product-specific, with some products increasing water activity with increasing temperature, while others decrease aw with increasing temperature.

Moisture content is a quantitative measure of the amount of water in a product.
Empirical measurement with no standard, with primary methods including loss on drying and titration.

Water activity affects microbial growth, with aw values below 0.80 generally inhibiting microbial growth.
Cheese and Cracker System experiment: aw values increased/decreased with moisture content changes.

MSI measures the change in free energy of water in a food material.
Constructed using resorption (or adsorption) method, where a completely dry food material is incubated in controlled humidity chambers at constant temperature.
MSI shapes and positions depend on the composition of the food material and phase states of the components.

MSI relates to chemical and physical changes, microbial spoilage, and stability of foods.
Change in the monolayer moisture content with temperature affects the stability of foods.

Constitutional water: an integral part of non-aqueous constituents, experiencing phase changes and becoming hygroscopic (e.g., sorbitol and sucrose).
Other water states: non-hygroscopic (e.g., mannitol), or coupled states in foods at different water content levels.

Caking is a water activity, time, and temperature-dependent process, affecting powder flow and stability.
Water activity and food stability are closely related.

Reaction rate increases as water activity increases from the monolayer value.
Common reactions related to chemical stability include Maillard browning, lipid oxidation, hydrolysis, nutrient degradation, and enzymatic reactions.

Methods include dehydration, edible films and coatings, and additives/ingredients involved in water binding (e.g., humectants, sugars, and salt).
Water activity affects moisture migration, product formulation, microbial growth, texture, and chemical stability.