Chapter 7
Water:
The Universal Solvent
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Objectives
• Describe how the structure of a water
molecule affects water’s physical
characteristics.
• Demonstrate a function of water in food
preparation.
• Explain how the water content of food
affects how the food will react during
preparation and storage processes.
continued
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Objectives
• Identify four functions of water in the
body.
• List common contaminants in water.
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Water
• Water is
– the only substance found in abundance in the
solid, liquid, and gaseous state
– the main component of many foods
– a nutrient necessary to sustain life
• Nutritionally, water
– helps control body temperature
– transports nutrients and waste products
– provides the solution for metabolic reactions
continued
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Water
• Water also
– influences the texture, appearance, and taste
of food
– is an important heat medium in cooking
– is an important solvent for cleaning and
sanitation
– is critical in food preservation
– determines the likelihood of food spoilage by
its presence or absence
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Types of Covalent Bonds
• Water (H2O) has 2 hydrogen atoms and one
oxygen atom
– held together by covalent bonds
• A nonpolar covalent bond is electrically
neutral since electrons are shared equally
by the atoms in the molecule
• Water has a polar covalent bond, or an
unequal sharing of electrons
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Hydrogen Bonds
• The positive hydrogen end of one water
molecule is drawn to the negative oxygen
ends of other water molecules
– This forms a hydrogen bond that is
intermolecular, or between molecules
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Surface Tension
• Hydrogen bonds in water create a greater
surface tension than most compounds,
allowing water to
– cling to something else as well as itself
– have a higher melting and boiling point than
other compounds
– freeze faster than it thaws
– form a crystalline structure in the solid state
continued
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Surface Tension
• Hydrogen bonding
helps to dissolve polar
substances, making
water a great solvent
– Sugars, starches, and
proteins form hydrogen
bonds with water
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Pressure, Temperature, and
Phase Changes
• Atmospheric pressure impacts the
boiling and freezing points
– Water boils at lower temperatures at high
altitudes and at higher temperatures at low
altitudes
– High altitude baking considerations such as
increasing the amount of flour, water content,
and oven temperature need to be considered
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Impact of Impurities in Water
• Water is not usually found in pure form
because it is such a great solvent
• An impurity in water may change its
– physical and chemical characteristics
– flavor and color
– boiling and freezing points
– hydrogen bonding
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Functions of Water in Food
Preparation
• Water transfers heat energy into food
– Water boils at a constant temperature
– Steam is as hot as boiling water when not
under pressure, but is hotter under pressure
• Steam
– leaves food more flavorful and nutritious than
boiling
– leavens baked goods
continued
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Functions of Water in Food
Preparation
• Gas-in-water solutions
– Carbon dioxide is the gas solute dissolved in
water when making carbonated beverages
– Oxygen also dissolves in water and is partially
responsible for the taste of water
• Liquid-in-water solutions
– Alcoholic beverages, vinegars and fruit juice
concentrates are examples
continued
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Functions of Water in Food
Preparation
• Solid-in-water solutions
– If a solid is dissolved in water, the chemical
properties will be different than pure water
– Salt and sugar lower the freezing point and
increase the boiling point of water
– Tea and coffee are flavor compounds dissolved
in water
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Water Content in Foods
• Water is a major part of most foods
– Fruits and vegetables are over 70% water
– Bread is 36% water
– Popcorn is 4% water
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continued
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Water Content in Foods
• Water becomes part of the structure of
food in 3 ways
1. Free water
– is easily separated from food tissue
– often contains dissolved compounds
– boils and freezes easily
– readily evaporates when foods are dried
continued
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Water Content in Foods
2. Bound water
– is tied to the structure of larger molecules
– does not easily freeze or boil
– chemically reacts as part of the larger molecule
3. A hydrate
– is any compound loosely bound with water
– must be boiled to be free of water, known as
anhydrous
continued
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Water Content in Foods
• The water type impacts perishability
– Water bound to other compounds is not
available to support food spoilage
– Water in carrots is mostly bound to starch
molecules, while in milk, it’s mostly free
– Both are 88% water, but carrots are much less
perishable
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continued
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Water Content in Foods
• Water activity (Aw) takes into account the
water available to support enzyme activity
and microorganism growth
– It is measured in values from 0 to 1
– The higher the number is, the more perishable
the food will be
– Canned foods are much more perishable than
dried
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Functions of Water in the
Body
• The 4 main functions of water in the body
are to
– maintain body temperature
– transport nutrients and waste products
– serve as a reactant in metabolism
– become part of body tissue
• The water you drink and the water found in
foods you eat help you stay hydrated
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A Safe Water Supply
• Rainwater that enters lakes and rivers may
be filtered to become drinking water
• A contaminant or pollutant is anything
that makes a substance like water impure
or unsafe, such as
– human and animal wastes
– chemicals and factory waste
– garbage
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Common Pollutants
• Biological contaminants
– Large numbers of bacteria, protozoa, viruses,
and organic waste deplete oxygen from rivers,
lakes, and water supplies
• Chemical contaminants
– Metal ions such as calcium or magnesium
cause hard water
– Acid rain changes the pH of water
continued
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Common Pollutants
• Physical contaminants
– Garbage and litter such as cans, bottles, and
plastics harbor bacteria, cause physical harm,
and break down into toxins that enter the
water supply
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Recap
• The structure of water gives it many
unique characteristics and functions in
the human body and in food production
• In food preparation, water acts as a
– heat medium
– leavening agent in baked goods when in
the gaseous phase
– solvent of gases, liquids, and solids
continued
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Recap
• Water becomes part of the structure of
food in the form of
– free water
– bound water
– a hydrate
• Foods with higher water activity (AW)
better support enzyme activity and
microorganism growth
continued
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Recap
• Water is necessary in the body to
– maintain body temperature
– transport nutrients
– serve as a reactant in metabolism
– become part of body tissues
• Common contaminants in water are
– biological pollutants such as bacteria
– chemical contaminants such as metal ions
– physical contaminants such as litter
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