Water is the foundation of life and food. Its unique molecular structure gives it extraordinary properties that shape how foods behave. From cooking to preservation, water's physical and chemical traits are key to understanding food science.

Water's polarity, hydrogen bonding, and thermal properties affect how it interacts with food components. Its role as a solvent and pH influencer impacts food texture, stability, and safety. These properties are crucial for food processing and storage.

Molecular Properties

Polarity and Hydrogen Bonding

• Water is a polar molecule due to the unequal sharing of electrons between oxygen and hydrogen atoms
  • Oxygen atom has a partial negative charge while hydrogen atoms have a partial positive charge
• Polarity allows water molecules to form hydrogen bonds with each other
  • Hydrogen bonding occurs when the positively charged hydrogen atom of one water molecule is attracted to the negatively charged oxygen atom of another water molecule
• Hydrogen bonding gives water many of its unique properties such as high surface tension, cohesion, and adhesion
  • Cohesion refers to the attraction between water molecules, allowing them to stick together (droplet formation)
  • Adhesion is the attraction between water molecules and other substances (capillary action in plants)

Surface Tension and Density Anomaly

• Surface tension is the tendency of water molecules to be attracted to each other at the surface, creating a thin "skin" on the surface
  • Results from the strong cohesive forces between water molecules due to hydrogen bonding
  • Allows insects to walk on water and enables the formation of bubbles and droplets
• Water exhibits a density anomaly, where it reaches its maximum density at 4°C (39.2°F)
  • As water cools from 4°C to 0°C, it expands and becomes less dense
  • This unique property allows ice to float on liquid water, providing insulation for aquatic life in frozen water bodies

Thermal Properties

Specific Heat Capacity

• Water has a high specific heat capacity, meaning it requires a large amount of energy to increase its temperature
  • Specific heat capacity is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius
• The high specific heat capacity of water allows it to absorb and release large amounts of heat energy without significant temperature changes
  • Helps regulate temperature in living organisms and the environment (oceans moderating climate)
  • Useful in food processing, such as cooking and pasteurization, where stable temperatures are required

Latent Heat

• Latent heat is the energy absorbed or released by a substance during a phase change without a change in temperature
  • Latent heat of fusion is the energy required to convert a solid to a liquid at its melting point (ice to water at 0°C)
  • Latent heat of vaporization is the energy required to convert a liquid to a gas at its boiling point (water to steam at 100°C)
• Water has high latent heat values, requiring significant energy for phase changes
  • Helps regulate temperature during phase changes, such as evaporative cooling (sweating) in living organisms
  • Utilized in food processing techniques like freeze-drying and evaporation to remove water from foods

Chemical Properties

Solvent Properties

• Water is an excellent solvent for many substances due to its polarity and ability to form hydrogen bonds
  • Polar and ionic compounds (salt, sugar) readily dissolve in water, forming aqueous solutions
  • Hydrophilic substances (starches, proteins) interact favorably with water and can be dispersed or solubilized
• Water's solvent properties play a crucial role in various food systems
  • Dissolution of ingredients, such as sugar and salt, in food formulations
  • Extraction of bioactive compounds (polyphenols) and flavors from plant materials (tea, coffee)
  • Dispersion of hydrocolloids (gums, starches) to create desired textures and stabilize emulsions

pH

• Water undergoes self-ionization, forming hydronium ions (H3O+) and hydroxide ions (OH-)
  • The concentration of these ions determines the pH of an aqueous solution
  • pH is a measure of the acidity or alkalinity of a solution, with a scale ranging from 0 (highly acidic) to 14 (highly alkaline), and 7 being neutral
• The pH of water and aqueous solutions in food systems influences various properties and reactions
  • Enzyme activity and protein stability are pH-dependent, with optimal ranges for specific enzymes and proteins
  • pH affects the solubility, color, and stability of pigments (anthocyanins) and other compounds in foods
  • Control of pH is essential in food preservation, as it can inhibit microbial growth and ensure product safety (acidification of canned foods)