Food Chemistry: Properties of Water

Water is the main component in lots of foods. Water is a big deal for food quality! Understanding its properties and how it behaves is super important.

Water changes its physical properties based on temperature. It can exist as a solid (ice), a liquid (water), and a gas (vapor).

Ice is water in its frozen state, forming a rigid lattice structure with a fixed shape.

A water molecule is made of one oxygen atom and two hydrogen atoms. It has a bent shape with an angle between the hydrogen bonds.

Oxygen in a water molecule has 6 electrons. It uses sp3 hybrid orbitals to hold these electrons. These orbitals extend outward like the corners of a pyramid (tetrahedron).

The oxygen in a water molecule has a stronger pull on the electrons than the hydrogen atoms. This makes the O-H bond slightly ionic.

In a water molecule, the two O-H covalent bonds have a bond angle of 104.5 degrees. This angle is the reason water's shape is bent.

Water molecules have two pairs of electrons that don't form bonds with hydrogen atoms. These non-bonding electrons contribute to water's special characteristics.

Water molecules that are chemically bonded to a substance.

A primary method for determining moisture content in a sample involving heating the sample and measuring the weight loss.

A type of loss on drying method where a sample is heated in a forced-air oven to evaporate moisture.

A type of Loss on Drying method where the sample is heated in a vacuum oven to remove moisture.

A method for determining moisture content by distilling the sample with a solvent, separating the water, and measuring its volume.

Type of distillation where the sample is heated directly in a solvent, and the water vapor is collected and measured.

Type of distillation where the sample is refluxed with a solvent, and the water vapor is collected and measured.

A widely used chemical reaction method for moisture determination involving titrating a sample with Karl Fischer reagent.

A method for determining water content in food that involves reacting the water in the sample with iodine and sulfur dioxide, and measuring the amount of iodine consumed.

The volume of Karl Fisher reagent (KFR) required to react with a specific weight of water.

A method for calculating the water content of a sample using the volume of KFR needed to titrate the sample and the KFR moisture equivalence.

A method for determining moisture content in foods based on the amount of water lost through evaporation when the food is heated.

A method for measuring moisture content based on the electrical properties of water.

A method for determining moisture content based on the density of the food sample.

A method for determining moisture content based on the refractive index of the food sample.

The arrangement of water molecules in ice allows for more space between them compared to liquid water due to the formation of hydrogen bonds.

Water molecules are held together by weak bonds called hydrogen bonds. These bonds form constantly, break, and reform, creating a dynamic structure that allows for some movement.

The presence of dissolved salts or molecules with polar or hydrophobic groups can disrupt the hydrogen-bonded structure of water. This disrupts the dynamic equilibrium of water molecules.

The ease of water removal from food depends on how it's bound. Water in food exists in three forms: free, adsorbed, and water of hydration.

Free water behaves like normal water, acting as a solvent for salts and a dispersing agent for colloids.

Adsorbed water is bound tightly to proteins, cell walls, or in the protoplasm. It doesn't act as a solvent.

Water of hydration is chemically bound to molecules in the food. This type of water is very difficult to remove.

The moisture content of food can influence which measurement method is most appropriate. It can also help determine the required accuracy of the measurement.

Each water molecule forms four hydrogen bonds with neighboring water molecules. These bonds are formed between the oxygen atom's lone pairs (acting as acceptors) and the hydrogen atoms of other water molecules (acting as donors).

The arrangement of hydrogen bonds in water creates a three-dimensional network, contributing to its unique physical properties.

The polarity of water molecules is strengthened by the hydrogen bonds that extend across multiple molecules. This results in a larger dipole moment for the entire network and a high dielectric constant.

Protons can rapidly transfer between water molecules along the hydrogen bond network. This process forms the hydrated hydronium ion (H3O+).

The arrangement and bonding of water molecules in ice and liquid water differ significantly due to the influence of hydrogen bonds.

The coordination number in ice is 4, meaning each water molecule is directly bonded to four others. Liquid water has a higher coordination number due to closer packing and a different bond angle.

The oxygen-oxygen distance in ice is 0.276 nm due to the open, structured lattice. The covalent O-H bond distance is 0.101 nm, while the hydrogen bonded O-H distance is 0.175 nm.

The smaller bond angle in liquid water allows for a more compact structure, increasing coordination number and leading to higher density compared to ice.

The relationship between water activity (aw) and the equilibrium moisture content of a food at constant temperature and pressure.

A measure of the free water available for microbial growth and chemical reactions in food. It ranges from 0 (completely dry) to 1 (pure water).

A process that aims to reduce water content in a food, often to improve shelf life and prevent spoilage.

A process where a food is soaked in a concentrated sugar or salt solution to draw out moisture and increase the concentration of the solute.

A preservation method that involves lowering water activity to inhibit microbial growth.

A process that removes water from a food product, typically by heating or applying vacuum to increase the rate of evaporation.

The process of freezing a food product to inhibit microbial growth by lowering the temperature below the freezing point of water.

A method of increasing the fat content of a food, which can indirectly lower water activity by displacing water.