Water

Question 1

Importance of water in food

Answer 1

Affects texture (dry and brittle vs. moist and soft)

Enables enzyme activity and chemical reactions to occur (acts as a solvent)

Supports growth of microorganisms

Allows large molecules like polysaccharides and proteins to move about and interact

Conducts heat within food

Question 2

Structure of water

Answer 2

Polar

Covalent bonds between H and O but Hydrogen bonds between water molecules

Question 3

Freezing point

Answer 3

To depress the freezing point, add a soluble substance (sugar) or an ionizing substance (salt)

Question 4

Boiling point

Answer 4

Boiling point decreases as atmospheric pressure decreases

Food processing plants use partial vacuum to lower pressure and boiling point

Question 5

Flow

Answer 5

Water molecules are small, liquid water is thin

Food gets thicker as ingredients are added

• Flow eventually flow stops
• Food becomes brittle and crispy (glass)

Question 6

Surface tension

Answer 6

Affinity of water molecules in the liquid state for each other above all else

Inward pull of molecules on surface

No affinity for air or molecules on solid surface

Important for mixing powders with water

Question 7

Dissolving

Answer 7

Sugar, salt, etc. is torn out of its crystal structure and surrounded by water molecules

Water also dissolves many proteins, carbohydrates, and minerals, but not lipids

Heat increases the effect (water molecules move faster)

Question 8

pH

Answer 8

Acids taste sour/tart and bases taste bitter

pH changes kill microbes by affecting their proteins

Changes in pH affect proteins (they stick together), carbohydrates (can disintegrate), and minerals (how they dissolve)

Most foods are either acidic or neutral

Question 9

Water hardness or softness

Answer 9

Hard water contains a combination of Ca and Mg carbonate, Ca and Mg sulfate

Boiling precipitates Ca and Mg bicarbonates
-Temporarily hard water
Boiling does not precipitate Ca or Mg sulfate
-Permanently hard water
Interactions between salts and food components
-Tannins in tea and coffee
-Pectins in dried legumes

Question 10

Forms of water in food

Answer 10

Solvent water
-Free water
Absorbed water
-Thin film
Water of hydration
-Chemical component of sugars, salts, protein gels
Bound water
-Unavailable as a solvent
-Not free water
-Entrapped by matrix

Question 11

Water activity (aw)

Answer 11

Measures energy status of water within a system

Uses for aw data

• Control microbial growth
• Predict affects of temperature
• Control moisture migration
• Control rates of reactions
• Avoid caking or clumping
• Tailor packaging