Chapter 7: Water: The Universal Solvent Flashcards
In what states can water be found in?
Solid, liquid, and gaseous
What are the 3 nutritional functions of water?
1) Helps control body temperature
2) Transports nutrients and waste products
3) Provides the solution for metabolic reactions
What are the 5 food science functions of water?
1) Influences the texture, appearance, and taste of food
2) Important heat medium in cooking
3) Important solvent for cleaning and sanitation
4) Critical for food preservation
5) Determines the likelihood of food spoilage by its presence or absence
Water is held up by what type of bond?
Polar covalent bond
Define nonpolar covalent bonds.
Electrically neutral since electrons are shared equally by the atoms.
Define polar covalent bonds.
Unequal sharing of electrons, which creates a dipole moment.
Define a hydrogen bond.
Weak bond resulting from an electrostatic attraction between a proton in one molecule and an electronegative atom in the other.
Are hydrogen bonds intramolecular or intermolecular?
Intermolecular
How are hydrogen bonds connected in a water molecule?
Positive H end of one H2O molecule is drawn to the negative oxygen ends of other H2O molecules
What do H-bonds create for surface tension?
H-bonds in H2O create a high surface tension
What are the 4 things surface tension allows?
1) Clings to something else
2) Have a higher melting and boiling point
3) Freezes faster than it thaws
4) Forms a crystalline structure in a solid state (ice)
Why is H2O a great solvent?
H-bonding helps to dissolve polar substances
What can form H-bonds with H2O?
Sugars, starches, and proteins (polar molecules)
How does higher altitude affect boiling point?
H2O boils at a lower temperature, decreasing atmospheric pressure
How does lower altitude affect boiling point?
H2O boils at a higher temperature, increasing atmospheric pressure
What are some higher altitude baking considerations?
- Higher amounts of flour
- Higher water content
- Oven temperature needs to be considered
Why is H2O not usually found in its pure form?
Since it is such a great solvent
What are the 4 things impurities change?
- Physical and chemical characteristics
- Flavour and colour
- Boiling point and freezing point
- Hydrogen bonding
What temperature does H2O boil at? Is it constant?
100oC, yes
What is the temperature of steam?
As hot as boiling water if not under pressure
What is the temperature of steam if under pressure?
Hotter than boiling water
What are the 2 things steam does in food preparation?
1) Leaves food more flavourful and nutritious than boiling
2) Leavens baked goods
What are the 2 functions of gas-in-water solutions in food preparation?
- CO2 is the gas solute dissolved in H2O when making carbonated beverages
- Oxygen also dissolves in H2O and is partially responsible for the taste of H2O
What is the function of liquid-in-water solutions in food preparation?
Alcoholic beverages, vinegars, fruit juice concentrates
What changes when a solid it dissolved in water?
Chemical properties
What happens when salt or sugar is dissolved in water?
Lower the freezing point and increase the boiling point of water
What are tea and coffee?
Flavour compounds dissolved in H2O
What are the 3 ways water becomes a structure of food?
1) Free Water
2) Bound Water (Water Activity)
3) Hydrate
What affects perishability?
Water type: H2O bound to other compounds is not available to support food spoiling
Explain why ice floats in water.
H2O has greater space when frozen than liquid, due to repelling of like charges.
Ice = less dense than water, so they float
How does a pressure cooker work?
Steam builds, pressure builds, water needs more energy, higher temperature to boil, which will cause foods to cook faster
Why does hot tap water contain more impurities than cold?
Heat causes impurities from pipes to dissolve into water
Why do we add salt to boiling water?
It will raise the boiling point, gives pasta desired firm texture
Why does it take slightly longer to cook foods in steam than boiling water?
Steam is a poor conductor of heat (if not under pressure)
Why does steam cook faster if under pressure?
Boiling point increases under pressure -> steam has higher T
How can steam be used as a leavening agent?
Popovers
What is the ideal brewing temperature for teas and coffees?
Just below the boiling point
What type of water are grapefruits?
Free water
What type of water is found in protein and starch molecules inside fruits, meats and vegetables?
Bound water
What type of water is found in plant and animal tissues inside the cells?
Hydrate
What is an anhydrous compound?
Compounds that have water driven off, free of water
Define Water Activity (Aw). How is it measured?
Takes into account the water available to support enzyme activity and microorganism growth
The higher the water activity (0-1), the more perishable the food will be
Name the 4 bodily functions of water.
1) Maintain body temperature
2) Transport nutrients and waste products
3) Serve as a reactant in metabolism
4) Become part of body tissue
How do we get drinking water?
Rainwater that enters lakes and rivers may be filtered to become drinking water.
Define contaminants.
Anything that makes a substance like water impure or unsafe.
What kind of bacterias, viruses or hormones can you get from contaminants?
Salmonella, E-coli, antibiotics, estrogen, garbage
Name the 3 classes of common pollutants.
1) Biological contaminants
2) Chemical contaminants
3) Physical contaminants.
Give examples of biological contaminants.
bacterias, protozoa, viruses, organic waste
Give examples of chemical contaminants.
metal ions, antibiotic compounds, endocrine disruptors, acid rain
Give examples of physical contaminants.
garbage and litter
