Download Scientific Principles: Chemical Properties

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Goals & Objectives
• To explain the Periodic Table of the
Elements
• To identify and explain how chemical
symbols, formulas and equations are
used in food science
• To discuss elements, compounds,
mixtures and formulas
• To compare elements and compounds
• To analyze chemical and physical
changes in food
• To examine the occurrence of
specific chemical reactions
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Main Menu
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Basic Chemistry
Principles
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Atoms
• Are the basic unit of matter
• Consist of a dense, central
nucleus composed of protons and
neutrons
• Are surrounded
by a cloud of
electrons
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Components of Atoms
• Include:
– neutrons- large
particles with no
net charge located
in the nucleus
– protons- large,
positively charged
particles located
in the nucleus
– electrons- small, negatively charged
particles located in atomic orbitals
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Elements
• Are pure substances consisting
of one type of atom
• Cannot be broken down or
changed into another substance
• Combine with other elements to
form compounds
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Compounds
• Are substances composed of
two or more elements in
specific ratios and bonded
together through chemical
forces
– Example: Carbon dioxide is
always composed of one carbon
atom and two oxygen atoms
• Are classified as either
covalent or ionic in foods
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Covalent Compounds
• Are also known as molecular
compounds
• Occur between the non-metal
elements
• Share the electrons from each
atom
• Are molecules
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Ionic Compounds
• Occur between metals and nonmetals
• Are held together by ionic bonds
– electrons are donated from one atom
to another giving one atom an
overall negative charge and the
other atom an overall positive
charge
• Contain atoms in which the total
number of electrons is not equal
to the number of protons
• Can consist of one element or
multiple elements such as NaCl
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Ions
• Are either positively or
negatively charged
• Can be a single atom
(monatomic ion)or multiple
atoms (polyatomic ion)
– ions of many elements and
compounds exist such as hydrogen,
sodium, ammonium and sulfate
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Pure Substances
• Can be formed from elements
or compounds
• Consist of only one
component with definite
physical and chemical
properties
• Have the same composition
throughout
– E x a m p l e : O2 o r p u r e w a t e r
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Mixtures
• Are substances held together by
physical forces
– this means individual molecules are near
each other without altering their
chemical structure
• Can be homogeneous or heterogeneous
Homogeneous: mixtures which are the same
throughout, with identical properties throughout
the mixture
Heterogeneous: mixtures which have different
properties when sampled from different areas
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Mixtures & Pure Substances
Example
• Tap water contains molecules
which are not water molecules,
making it a
mixture
• Distilled
water contains
only water molecules making it
a pure substance
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Bonds
• Between atoms influence the
molecule’s properties
• Are classified as:
– hydrogen
– covalent
– ionic
– polar
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Bonds
• Example of this difference are
hydrogen and covalent bonds
– In a covalent bond, each atom
equally shares the combined
electrons; this type of bond is
harder to break than a hydrogen
bond.
– Hydrogen bonds are commonly found
between water molecules and
proteins. The bond is the main
reason for the properties of water
and instrumental in the
‘unzipping’ of DNA. This bond is
only about five to ten percent of
the strength of a covalent bond.
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Periodic Table
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Periodic Table
• Was created by Russian
Chemist Dmitri Mendeleev in
1869
• Displays all of the known
elements
• Arranges all of the
elements based on
certain properties
• Provides a framework
to classify, organize
and compare chemical
behavior
• Can be used in all
fields of science
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Periodic Table
• Uses a unique chemical symbol
to identify each element
• Arranges elements from left
to right and top to bottom in
order of increasing atomic
number
– the order generally coincides
with increasing atomic mass
• Has rows called periods and
columns called groups
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Chemical Symbol
• Is a shortened version of the name
of an element
• Represents an element in chemical
formulas
• Uses only one or two letters to
represent an elements
– for example, Hydrogen, Nitrogen and
Oxygen are represented by H, N and O
– if two elements have the same first
letter, two letters comprise the
symbol
• for example, Calcium and Chlorine both
start with a “c” but are represented by Ca
and Cl
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Atomic Number
• Is the number of protons in an
atom
• Defines the element
– for example:
• all carbon atoms have six protons so its
atomic number is six
• all oxygen atoms have eight protons so
its atomic number is eight
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Atomic Mass
• Is the average mass of an the
protons and neutrons present in
an element
• Is measured in atomic mass
units (amu)
– Atomic mass units measure the
approximate mass of one proton or
neutron
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Periods
• Are the rows of the Periodic Table
• Contain elements which have the same
number of atomic
orbitals for its
electrons
• Are given a
period number
– there are seven
periods in the Periodic Table
Atomic orbitals: shell which holds electrons
Period number: the highest unexcited energy
level for an electron in the element
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Groups
• Are the columns of the Periodic Table
and are also known as families
• Contain elements which share common
properties
• Are elements which
have the same number
of electrons in their
outer orbital
– the outer electrons
are called valence
electrons
• Have Roman numerals
listed above each
group in the
Periodic Table to indicate
how many valence electrons are present
• for example, group VA will have five
valence electrons
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Valence Electrons
• Are the electrons located in
the outermost occupied shell
in an atom
• Participate in chemical
bonding
• Determine the properties and
chemical reactivity of the
element
• Aid in dividing the elements
into representative elements
and nonrepresentative elements
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Major Families of Elements
• Alkali Metals
– are located in Group One
– are very reactive
– include the following elements:
•
•
•
•
•
•
Lithium (Li)
Sodium (Na)
Potassium (K)
Rubidium (Rb)
Cesium (Cs)
Francium (Fr)
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Major Families of Elements
• Alkaline Earth Metals
– are located in Group Two
– are the second most reactive group
of elements
– include the following elements:
•
•
•
•
•
•
Beryllium (Be)
Magnesium (Mg)
Calcium (Ca)
Strontium (Sr)
Barium (Ba)
Radium (Ra)
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Major Families of Elements
• Transition Metals
– are located in the middle portion of
the periodic table
– are very hard
– have high melting and boiling points
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Major Families of Elements
• Halogens
– are very reactive
– can be found in Group 17
– include the following elements:
•
•
•
•
•
Fluorine (F)
Chlorine (Cl)
Bromine (Br)
Iodine (I)
Astatine (At)
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Major Families of Elements
• Noble Gases
– can also be called inert gases
– are located in Group 18 which is
also called Group Zero
– are not reactive
– include the following elements:
•
•
•
•
•
•
Helium (He)
Neon (Ne)
Argon (Ar)
Krypton (Kr)
Xenon (Xe)
Radon (Rn)
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Major Families of Elements
• Lanthanide Series
– consist of 15 elements
– can be found naturally occurring on
Earth
– has one radioactive element
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Major Families of Elements
• Actinide Series
– consist of 15 elements
– are all radioactive compounds
– include some elements which are not
found in nature
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Chemical
Formulas &
Reactions
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Chemical Formulas
• Are a combination of elemental
symbols and subscript numbers
that are used to show the
composition of a compound
• Represent compounds
– for example, the chemical formula
f o r a l u m i n u m o x i d e i s Al2O3
• this means there are two aluminum
atoms and three oxygen atoms
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Ionic Compounds
• Are composed of cations and
anions
• Are held together by the strong
attraction of the positive and
negative charges of the ions
• Are neutral compounds
• Are formed between metals and
nonmetals
– for example: sodium chloride or
table salt (NaCl)
Cation: ion with a positive charge
Anion: ion with a negative charge
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Chemical Formulas
• Have a charge sum of zero
– the positive and negative charges
cancel each other out
• for example: if a bond was formed
between Mg+2 and Cl– to equal out the charges it would take 2
Cl- and 1 Mg+2
– so the chemical formula would be MgCl2
Hint: Always use the charges when writing a
chemical formula.
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Chemical Formulas
• Polyatomic ion example
– a bond is made between lithium
Li+1 and sulfate S O 4 - 2
• to equal out the charges it would
take two L i + 1 and 1 S O 4 - 2
• so the chemical formula would be
L i 2S O 4
Hint: When working with polyatomic ions, DO NOT
break it up or change the numbers in the ion.
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Chemical Formulas
• Covalent or molecular compound
example
– prefixes give the number of each
element present in a molecule
• carbon dioxide = C O 2
• dinitrogen monoxide = N 2 O
• dichloride heptoxide = C l 2 O 7
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Prefix Help Chart
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Chemical Reactions
• Occur when a chemical change
occurs
• Begin with one
compound and
turn it into
another
• Can include ions,
molecules or pure atoms
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Chemical Reaction Rate
• Is the speed at which the
reaction occurs
– a lower reaction rate means the
molecules combine at a lower speed
than a reaction with a higher rate
• Can be influenced by the
collision theory
– states that the more collisions in
a system, the more likely
combinations of molecules will
happen
• the higher the number of collisions,
the faster the reaction will occur
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Factors Affecting Reaction
Rate
• Include the following:
– concentration
– temperature
– pressure
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Concentration
• Increases the rate of reaction
if there is more of a
substance in a system
– there is a greater chance for the
molecules to collide
• Decreases the rate of reaction
if there is less of a
substance in a system
– there is a decreased chance for
the molecules to collide
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Temperature
• Increases the rate of
reaction if the
temperature is increased
– the atoms or molecules will
move more and are more
likely to collide
• Decreases the rate of
reaction if the
temperature is decreased
– the atoms or molecules move
slower and collide less
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Pressure
• Increases the rate of
reaction when pressure is
increased
– increases the number of
collisions between the atoms
or molecules
• Decreases the rate of
reaction when the pressure
is decreased
– the atoms or molecules will
not hit each other as often
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Reaction Rate
• Can be any of the following:
– forward rate
• the rate of the forward reaction
when reactants become products
– reverse rate
• the rate of the reverse reaction
when products become reactants
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Reaction Rates
• Net rate
– the forward rate minus the reverse
rate
• Average rate
– the speed of the entire reaction
from start to finish
• Instantaneous rate
– the speed of the reaction at one
moment in time
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Chemical Reactions
• Happen in several steps
– the rate for each step should be
measured
• the rate-limiting step is the slowest
step in the reaction and can determine
the overall rate of reaction
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Stoichiometry
• Is the study of the amounts of
substances involved in reactions
• Helps you to figure out how much
of a compound you need or how
much you started out with
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Stoichiometry Example
• To make sodium chloride (NaCl), you
start out with two ions Na+ and Cl- and
end up with the ionic compound NaCl
• When you look at the chemical formula,
you see that it takes one atom of sodium
to combine with one item of chlorine
• Stoichiometry aids us in determining the
amounts of substances needed to fulfill
the requirements of the reaction
• Stoichiometry tells us that if you have
100 atoms of sodium and only one atom of
chlorine you can only make one molecule
of sodium chloride.
100 Na + + 1 Cl
NaCl + 99 Na +
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Stoichiometry Example
• Let’s say you are mixing two hydrogen
gas molecules ( H 2 ) and one oxygen
gas molecule ( O 2 ) and add a spark
to it.
• You would have this equation:
2H2 + O2
• In order to make water you need two
hydrogen atoms for each oxygen to get
the H2O chemical formula
• Therefore the chemical reaction will
yield two H 2 O
2H2 + O2
2 H 2O
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Equilibrium
• Occurs when two reactants
combine to make a product and
the products then break apart
and turn back into the
reactants
– the reactants combining is a
forward reaction and the
products breaking apart is a
reverse reaction
• Exists when the forward
reactions equal the rate of
the reverse reaction
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Catalysts
• Increase reaction rate
• Lower the amount of energy
needed for a reaction to occur
• Aid a reaction in reaching its
activation energy
Activation Energy: the energy required
to make a reaction happen
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Inhibitors
• Decrease rate of reaction
• Have the ability to stop a
reaction from occurring
• Help to control the rate of
reactions
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Food Chemistry
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Food Chemistry
• Is a systematic evaluation and
understanding of water,
carbohydrates, lipids, proteins,
minerals and vitamins as they
undergo chemical interactions
during harvest, processing,
storage and distribution
• Is the study of chemical
processes and interactions of
all biological and nonbiological
components of food
• Encompasses the chemical makeup
of food
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Food Chemistry
• Is based upon the following
components of food:
– water
– carbohydrates
– lipids
– proteins
– enzymes
– vitamins
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Water
• Is a major component of food
• Is an excellent location for
bacterial growth and food
spoilage to occur
• Can be measured by obtaining
the water activity of a food
• Must be controlled in foods
to aid in food preservation
• Is controlled in foods by
dehydration, freezing and
refrigeration
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Water
• Is important in cooking and
food preparation
• Uses include:
– removing debris and the washing
of foods
– a substance in which to cook
food
– a solvent to disperse and
dissolve flavor additions
– adding moisture to foods
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Water
• Can be either hard or soft
– hard water
• any water containing an appreciable
quantity of dissolved minerals
– soft water
• any water in which the only
positively charged ion is sodium
Fun Fact: Rain water is considered “soft” until it
reaches the ground where it picks up minerals
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Hard Water
• Commonly has high levels of
calcium and magnesium
• Can cause build up on fixtures
such as faucets and shower
heads
• Decreases the effectiveness of
soaps and laundry detergents
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Hard Water
• Found in almost 85 percent
of American communities
• Can be corrected by adding
a water softener
– Sodium or potassium ions are
bonded to resin beads. Hard
water runs over the beads and
the minerals in the water
cling to the beads, releasing
the sodium and potassium ions
into the water
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Soft Water
• Does not contain any dissolved
minerals
• Increases the life expectancy
of plumbing systems and
appliances which use water
• Decreases:
– soapy residue on clothes
– mineral deposits on bathroom and
kitchen fixtures
– amount of soap and detergents
used
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Water
• Is found in three states:
– liquid
– gas
– solid
• Can be transformed from a solid by
the heat of fusion and from a
liquid to a gas by the heat of
vaporization
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Heat of Fusion
• Is the amount of energy required to
transform a substance from a solid
to a liquid
• Is measured in Joules or calories
• For water is 334 Joules per gram or
79.7 calories per gram
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Heat of Vaporization
• Is the amount of energy required
to transform a substance from a
liquid to a gas at the boiling
point of the substance
• Is measured in Joules or calories
• For water is 2260 Joules per gram
or 539 calories per gram
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Heat of Vaporization
• For water, is greater than
the heat of fusion
– Water has many unique chemical
properties. For more
information see:
The United States Geological Survey
Water Science for Schools
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Carbohydrates
• Are organic compounds which
consist of carbon, hydrogen
and oxygen
• Are classified as
monosaccharides,
disaccharides,
oligosaccharides and
polysaccharides
• Complete numerous functions
such as providing energy
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Carbohydrates
• Can be used as thickening
agents, sweeteners and for
texture in foods
• Form pastes when a mixture of
ground starch and water is
heated
– Heat is necessary for paste
formation
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Paste Formation
• Begins when the starch
granule swells with the
intake of water
• Proceeds when the granule
absorbs the maximum amount
of water and releases
amylose
• Completes when the starch
granule implodes
• Increases the viscosity of a
mixture
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Paste Formation
• Necessary for the creation of
such foods as:
– breakfast cereals
– pastas
– sauces
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Lipids
• Are a group of naturally
occurring molecules such
as:
– fats and oils
– waxes
– sterols
– monoglycerides
– diglycerides
– phospholipids
• Are naturally hydrophobic
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Lipids
• Are commonly referred to as
fats
• Come from both animal and
plant sources
• Provide tastes and textures
to foods
• Have a wide range of cooking
temperatures
• Can be used as a cooking
medium when melted at high
temperatures
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Lipids
• Are important in food
preparation
• Provide a pleasant mouth feel
and flavor to foods
• Provide the highest amount of
useable calories per gram
Fun Fact: Mouth feel is the sum of a food’s
physical and chemical reactions in the mouth.
Texture is the actual physical feeling of a food in
the mouth.
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Lipids
• Can:
– prevent foods from sticking to
cookware
– create fluffy and moist or flaky
baked goods
– transfer heat to food
– thicken or emulsify sauces
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Lipids
• Are available for cooking in
liquid and solid forms
• Must be observed closely while
using as temperature can have a
negative effect
• Have different smoke points
• Possess properties which can be
altered by light, temperature
and usage
Smoke Point: temperature at which cooking fats and
oils begin to smoke, emit odors and chemical
structures break down
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Temperature
• Melts solid fat when
increased
• Inconsistences over time
can cause chemical changes
in the fat resulting in
smell, taste and texture
changes
• At high degrees, degrades
cooking fats over time
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Temperature
• Can cause the fat in food
products to separate from
the food
– example: cheddar cheese cooked
for a long period of time at a
high temperature will release
fat, become tough and rubbery,
then crumble
• Ranges for each cooking fat
is different, so make sure
you keep this in mind when
choosing a cooking fat
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Proteins
• Are organic compounds made
of amino acids arranged in a
linear chain and folded into
a globular form
• Are essential for growth and
survival
• Can be found in legumes,
meat, poultry and seafood
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Proteins
• Are used in cooking for
texture, taste, appearance
and nutritional content
• In food preparation can be
used:
– as a base for a food product
– as binding agent
– to alter the texture of a food
product
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Proteins
• Are denatured in the cooking
process
• Can be used as emulsifiers
– egg yolks are used to bind oil
and water in mayonnaise
• Found in wheat are
responsible for the texture
of baked goods and pastas
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Proteins
• Must be present for the Maillard
reaction to take place
• Can be isolated from legumes, such
as soybeans, and added to other
protein sources, such as chicken,
to change the texture and
nutritional content of the final
product
Maillard Reaction: the coagulation of denatured
proteins with sugars resulting in a distinct flavor
and browned color; seen in caramelized onions and
dairy based caramels
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Enzymes
• Are proteins which serve
as catalysts used in
converting processes from
one substance to another
• Reduce the time and energy
required to complete a
chemical process
• Are used in baking,
brewing, dairy production
and fruit juices
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Vitamins
• Are nutrients required in
small amounts for essential
metabolic reactions in the
body
• Are either water or fat
soluble
• Can prevent disease
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Physical Changes
• Are any changes not involving a
change in a substance’s chemical
identity
• Occur when objects undergo a change
which does not change their chemical
nature
• Involves a change in physical
properties
– physical properties include the
following:
•
•
•
•
•
•
•
texture
shape
size
color
volume
mass
weight
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Common Physical Changes in
Food
• Include the following:
– cutting
– mashing
– boiling
– melting
– freezing
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Freezing
• Involves storing a food below the
freezing point of water
– safest temperature of freezer
storage is below 0°F
• Results in water transforming from
a liquid state to a solid state
• Can have adverse effects on food
quality
– texture change, especially if food
is not frozen quickly
– altered color
– freezer burn if exposed to air
– increased food preparation time to
account for defrosting time
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Chemical Changes
• Occur when bonds are broken
and new bonds are formed
between different atoms
• Take place in everyday food
production
• Include the following common
food reactions:
– Nonenzymatic browning
– leavening
– fermentation
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Nonenzymatic Browning
• Is browning caused by heat
degradation of sugars or by the
reaction between reducing sugars
and a free amino group
• Is commonly found in foods
• Increases when there is a rise in
temperature and an increase in pH
above 6.8
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Leavening
• Gives breads, cakes, muffins,
pancakes and other foods the
ability to rise and increase in
volume
• Occurs mainly during cooking
• Involves a water or gas
expanding for rising to occur
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Leavening
• Agents include:
– baking powder
– baking soda
– baker’s ammonia
– potassium bicarbonate
– yeast
– sourdough starter
91
Baking Powder
• A combination of baking soda,
cream of tartar and cornstarch
• Comes in several types
– single action- chemical reaction
occurs when the powder comes in
contact with moisture
– double action- chemical reaction
occurs in two stages:
• first when the powder is moistened
• second proceeds when heated
– phosphate- reacts when the powder
encounters moisture
92
Baking Powder
• Ingredients all play a
different role
– cream of tartar is the acid salt
in the baking powder and reacts
with the baking soda in the
presence of moisture
– cream of tartar/baking soda
reaction produces carbon dioxide
– cornstarch absorbs any excess
moisture which may enter the
reaction
93
Baking Powder
• Can drastically affect the
taste of a baked good
– makes food bitter and coarse
textured if over used
• Is best used in foods which
are not overly acidic
• Will lose effectiveness with
age due to moisture
interaction
94
Fermentation
• Is the conversion of
carbohydrates to alcohols and
carbon dioxide or organic
acids using yeasts or bacteria
under anaerobic conditions
• Implies the action of
microorganisms is desirable
• Is used in preservation
techniques to create lactic
acid in sour foods or for use
in pickling foods
95
Resources
“Chemical Properties”.Elmhurst College. Virtual Chembook.”
(2003). Retrieved from:
http://www.elmhurst.edu/~chm/vchembook.html
“Physical and Chemical Properties”. Class notes. Indiana
University Northwest. (2010). Retrieved from:
http://www.iun.edu/~cpanhd/C101webnotes/matter-andenergy/properties.html
“What is Food Chemistry?”. (2010). Deb Dommel. Retrieved from:
http://www.math.unl.edu/~jump/Center1/Labs/WhatisFoodChemist
ry.pdf
“Food Chemistry: Principles and Applications”. (2000).
Genevieve Christen & J. Scott Smith.
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Acknowledgements
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Maggie Bigham
Project
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Megan Mitchell
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