Water and Water Activity in Foods

Flashcards covering key vocabulary related to water, its properties, and its role in food science.

Water Activity

The measure of available/free water in a food matrix that can support microbial growth.

Chemical Properties of Water

Water has two hydrogen atoms bonded to one oxygen atom, creating a polar molecule with a permanent dipole.

Hydrogen Bonds

Weak attractions between the partial positive and negative charges of polar molecules, significant in water's unique characteristics.

Density of Water

Mass of water per unit volume; decreases with temperature increase due to slight volume increase.

Vapor Pressure

The pressure that gaseous molecules exert on the surface of a liquid, influenced by temperature and solutes.

Solubility

The ability of a substance (solute) to dissolve in a solvent (e.g., increasing temperature enhances solubility of solutes).

Free Water

Water molecules that are not bound to solutes, essential for microbial growth and chemical reactions.

Moisture Content

Total amount of water in a food, including both free and bound water.

Boiling Point Elevation

The increase in boiling point temperature caused by the addition of solutes, which requires more temperature to reach vapor pressure.

Ice's Lower Density

Ice has a lower density than liquid water due to its crystalline structure formed by stable hydrogen bonds.

Halophilic

Organisms that thrive in high salt concentrations.

Xerophilic

Organisms that thrive in dry environments with limited water availability.

Osmophilic

Organisms adapted to high osmotic pressures, typically found in environments with high solute concentrations.

Millard Browning Reactions

Chemical reactions that increase with higher concentrations of reactants as water activity decreases.

Physical Preservation Techniques

Methods such as drying, salting, syruping, and freezing that reduce water activity to preserve food.

Equilibrium Relative Humidity

The relative humidity measurement used to calculate water activity in food samples.