Water: Properties and Importance in Food Science

Importance and Properties of Water in Food Science

• Water is essential for all life and makes up most of the liquid in organisms.
• Many organisms live in liquid water or in environments dominated by it.
• Water (moisture) is an inorganic liquid chemical that is colorless, odorless, tasteless, and makes up most of the earth's hydrosphere and fluids in living organisms
• Nearly 75% of the Earth's surface is covered by water.
• Uses for water include drinking, cooking, personal washing, cleaning, sanitation, agriculture, livestock, landscaping, and recreation.

Water Characteristics and Properties

• Removing water from food or binding it with salts and sugars inhibits microorganism growth, which aids in preservation and extends shelf life.
• Water acts as a solvent or dispersing medium for various foods like milk and juices.
• Water can be dispersed in emulsions, like butter, margarine, and mayo.
• Water appears transparent, colorless, tasteless, and odorless; thick layers appear greenish-blue.
• Pure water is a poor conductor of heat and electricity.
• Intermolecular hydrogen bonding among water molecules leads to high melting and boiling points.
• Low ion content of water ensures purity and avoids interference with chemical reactions.
• Deionized water is used in food and beverage productions.
• Poor electrical and thermal conductance in food impacts heating efficiency, texture, preservation, and quality
• Pure water conducts electricity poorly, but dissolved ions increase its conductivity.
• Salt brining adds salt to increase water conductivity, improving moisture retention and flavor.

Water Structure

• Water's formula is H2O
• Two hydrogen atoms bond to an oxygen atom; this results in a bent shape.
• Oxygen atoms are electron-seeking (electronegative) compared to hydrogen.
• The oxygen atom in water has a partial negative charge.
• The hydrogen atoms in water have a partial positive charge.
• The distance between hydrogen and oxygen nuclei in water is 0.0957 nm.
• The angle between hydrogen atoms in water is 104.5°.
• Polarity allows water molecules to form hydrogen bonds.
• Water is a dipolar molecule with positive and negative poles positioned opposite each other.

Hydrogen Bonding

• Hydrogen bonds are strong and form between a polar hydrogen and another heavy atom (carbon, nitrogen, oxygen, or sulfur) in biological molecules.
• In the gas phase, hydrogen bonds between two water molecules have a strength of 22.7 kJ/mole.
• Hydrogen bond strength in liquids and solids heavily depends on the geometry and surrounding molecules.
• Hydrogen bonds in food processing affect the texture, stability, solubility, and overall quality of food products.
• When eggs are heated, hydrogen bonds in egg proteins break and reform, leading to coagulation.
• Starch and gluten interact with water via hydrogen bonds, which is related to softness and staleness in bread.
• Pectin molecules in jellies and jams form a network through hydrogen bonding, trapping water and creating a firm texture.

Water Anomalies

• Anomalous properties of water are unusual physical/chemical behaviors that differentiate it from other substances.
• Anomalies arise due to hydrogen bonding between water molecules:
  • Density Anomaly (ice is less dense than water)
  • High Boiling and Melting Points
  • High Specific Heat Capacity
  • High Surface Tension
  • High Latent Heat of Vaporization
  • Good Solvent (Universal)

Specific Heat Capacity

• Water's high specific heat: it can absorb or release large heat amounts with small temperature changes.
• Water absorption/retention impacts texture, stability, and quality.
• Water helps regulate temperature in food products and prevents rapid temperature fluctuations.
• The high specific heat is due to hydrogen bonds between water molecules.
• Most of the added heat energy is used to break bonds rather than raise the temperature.
• Water's ability to store and transfer heat efficiently is important, because:
  • Large bodies of water absorb heat during the day and release it at night, helping to moderate temperature changes in climate regulation.
  • Biological stability, water maintains stable temperatures in living organisms and prevents sudden temperature swings.
  • Water heats and cools slowly, making it useful in cooking, heating, and cooling.

Cohesion and Adhesion

• Cohesion is the tendency of water molecules to stay together in a puddle.
• Adhesion is the tendency of water molecules to stay connected to other surfaces, e.g. glass.

Surface Tension

• Surface tension is the tendency of a liquid's surface to resist external force due to cohesive forces.
• Molecules at the surface strongly attract, creating an "elastic" layer.
• Water has a high surface tension compared to most liquids.
• High surface tension helps stabilize emulsions.
• Food emulsifiers can reduce surface tension and create smooth mixtures, e.g. lecithin in egg yolks.
• Droplet formation happens from water forming beads because the molecules cling together.
• Insects walk on water because surface tension supports their weight.
• Capillary action is when high surface tension helps liquids rise in narrow tubes, also for plant water transport.

Water Activity and Food Stability

• Triple Point defines the equilibrium between ice, liquid water, and vapor, thus influencing food stability.
• Water activity (aw) determines food spoilage.
  • Low water activity in dried foods and honey prevents bacterial growth.
  • High water activity in fresh meat and dairy makes food more perishable.
• Controlling water content in processed foods extends shelf life.
• Correct packaging prevents moisture absorption, which reduces spoilage.

Phase Diagram and Triple Points

• Water’s phase transitions (solid-liquid-gas) play a critical role regarding food science and affecting food preservation, texture, cooking processes, and food safety.
• Freezing and preservation (solid to liquid): Water turns to ice at 0°C (32°F) at 1 atm.
• Freezing slows down microbial growth and enzymatic reactions, preserving food.
• Supercooling effect: sometimes water in food remains liquid below 0°C until it finds nucleation point to crystallize
• Frozen foods (vegetables, meats, seafood) maintain quality and reduce spoilage.
• Slow freezing leads to large ice crystals and grainy texture; Rapid freezing produces smoother textures.
• Cryopreservation of food samples at ~-196°C helps maintain food structures.

Types of Water

• Types of water include monolayer, capillary, and loosely bound
• Langmuir or monolayer water have an aw between 0 and 0.2
• Monolayer defines the amount of water that is strongly adsorbed to specific sites
• Capillary water has an aw between 0.3 and 0.8
• Capillary water is held in narrow channels between food components because of capillary forces
• Loosely-bound water has an aw between 0.8 and 1.0
• Molds and yeast start to grow when aw is between 0.7-0.8
• Bacterial growth starts at an aw of 0.8

Water Content

• Lettuce has 95% water content, cabbage has 92%

Structure of ice

• Ice has a lower density than liquid water, so ice floats on water.
• Ice in solid is more densely packed than in liquid.
• A given mass of ice occupies more volume than water due to H-bonding arrangement.
• Water's density is greatest at about 4 °C (39.2 °F).
• Ice is more buoyant so it forms at the surface of water bodies and freezes downward.
• Lakes and rivers don't freeze completely, and liquid water becomes winter refuge for aquatic life.
• Ice is a tetrahedral lattice where each water makes H-bonds to four other waters.
• The 2-2 H-bonding symmetry is an important feature of water
• The combined angle of H-O-H is 109.58, with the tendency of waters to repel each other electrostatically
• Ice floats on water and is essential for frozen food storage.
• Prevents complete freezing of liquid foods, preserving texture and consistency.
• Water has the highest density at 4C, as Brownian motion slows down and distance between water molecules starts to reduce

Polarity

• Polar liquids dissolve other polar liquids.
• Polar liquids will not mix with non-polar substances (oil doesn't mix with water).
• Hydrophobic substances repel water.
• Hydrophilic substances attract water.
• Water is known as the "universal solvent" because so many substances dissolve in it.
• Water dissolves many substances due to the high polarity of water molecule.

Capillary Action

• Capillary action: Water rises through a thin column
• Capillary action is from a combination of adhesion that attracts water molecules and from cohesion.
• Glass tubes and plant roots are good examples of capillary action.

Water role in food preservation

• Freezing: Convers liquid water to ice, which prevents microbial growth
• Dehydration: Removal of water as a vapor to inhibit spoilage
• Freeze-drying: Preserves food by sublimating frozen water
• Understanding water's physical properties is critical to food stability and preservation.

Implications for food chemistry

• Regulation in cooking prevents overheating; because foods with high water resist change.
• A steaming effect; steam carries large amount of heat, which enables gentle cooking.
• Evaporative cooling: When water evaporates, it cools the surface to prevent overheating.
• Moisture Retention & Preservation; dehydration controls the moisture loss and drying.
• Freezing & Storage Stability; foods high in water take longer to freeze/thaw due to heat retention.
• texture improves the juice by retaining moisture for baked and fried. Crisp vs soft
• High moisture level is how crisp or soft the item will stay