8/1/2012
Welcome!
• Presenters:
– Patti Rambo, Director, The Curriculum Center for Family and
Consumer Sciences, Texas Tech University, Lubbock, TX
– Leslie Thompson, Ph.D., Chair and Professor, Department of
Animal and Food Sciences International Center for Food, Texas
Tech University, Lubbock, TX
– Sandra Duke, Family and Consumer Sciences Education Graduate
Research Assistant, Texas Tech University, Lubbock, TX
Molecular Motion
8/1/2012
Molecular Motion
TEKS (14) The student explains how food
provides energy. The student is expected
to:
• (A) discuss molecular motion and
temperature
• (D) compare various temperatures on
rates of reaction
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Molecular Motion
• Objective: Student will demonstrate and
explain the effect temperature has on
molecular motion.
8/1/2012
Molecular Motion
• Color Changing Milk Experiment
– One cup of milk on plate
– Place food coloring in milk
– Place a drop of food coloring
•
Variables
– Hot milk
– Cold Milk
•
8/1/2012
Hypothesis?
Molecular Motion
Brownian Motion
• Random movement of atoms and
molecules suspended in a liquid or gas
• Motion is caused by collisions with
molecules of the surrounding medium
• Heat energy determines how fast
molecules move
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Molecular Motion
Kinetic Theory
• Matter is composed of small particles - atoms
and molecules
• Particles of matter are in constant vigorous
motion
• Helps explain:
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8/1/2012
Transfer of heat
Relationship between temperature, pressure and
volume of gases
Molecular Motion
Diffusion
• Spontaneous spreading out of something
• Random in nature
• Matter moves constantly!
8/1/2012
Foaming and Whipped
Cream
8/1/2012
Foaming and Whipped Cream
TEKS (19) The student understands
coagulation and coalescence process
associated with milk protein and cheese.
The student is expected to:
(F) Identify the factors that affect the
ability of cream to form a foam.
8/1/2012
Foaming and Whipped Cream
Objective: Students will demonstrate and
explain the effects temperature and
agitation have on foams formed from
cream
8/1/2012
Foaming and Whipped Cream
Whipped Cream Experiment
• Half-cup whipping cream (or other dairy
product of varying fat content)
• Place in screw cap plastic container
• Shake container vigorously
• Check consistency of foam approximately
every 2 min
• Continue agitation until foam breaks and
butter forms
8/1/2012
Foaming and Whipped Cream
Potential variables
•
Fat content of dairy product (evaporated milk 7.25%
fat, half and half 10 to 18%, light cream 18 to 30%,
light whipping cream 30 to 36%, heavy whipping cream
>36%)
•
Temperature of heavy whipping cream
•
Time of agitation
•
Age of whipping cream
•
Addition of sugar (when added, gradual addition or
dump method)
8/1/2012
Foaming and Whipped Cream
Foam: Dispersion consisting of a continuous
liquid phase and a discontinuous gas
phase
Examples:
Ice cream, angel food cake, meringues,
whipped toppings, soufflés
8/1/2012
Foaming and Whipped Cream
• Foams are formed when whipping or
agitation unfolds (denatures) proteins
creating a stable network that traps air
• Agitation unfolds proteins and
incorporates air
• Fat in whipping cream helps stabilize the
foam
8/1/2012
Foaming and Whipped Cream
The most stable dairy foams are produced
at lower temperatures.
8/1/2012
Egg Foams
8/1/2012
Egg Foams
TEKS (4) The student analyzes the role of
acids and bases in the food sciences. The
student is expected to:
• (E) Discuss ways pH is related to the
properties of food, its safety and its
freshness
8/1/2012
Egg Foams
TEKS (18) The student describes the
properties of proteins and amino acids.
The student is expected to:
• (F) List factors that affect the stability of
egg foam
8/1/2012
Egg Foams
Objective: The student will assess how pH
affects the physical properties of eggs.
8/1/2012
Egg Foams
• As shell eggs age they loose water and CO2
• This cause the loss of the carbonate buffer
• As the buffer is lost the pH of the egg increases
• As pH of albumen increases the thick albumen
becomes thinner
• As the albumen thins it foams more easily but
is much less stable
8/1/2012
Egg Foams
• As eggs are stored the pH increases from
about 7.2 to 9.5
• pH changes affect foamabilty and foam
stability
• Ovomucin is the primary protein in eggs
responsible for foaming and foam
stability
8/1/2012
Egg Foams
• Freshly laid eggs are USDA Quality Grade
AA
• As eggs are stored the quality grade
decreases from AA A
B
• Foam stability decreases as quality grade
decreases
8/1/2012
Egg Foams
• Lipids interfere with egg foaming and
foam volume
• Factors such as temperature, age of the
egg, presence of sugars, presence and
types of lipids, pH and other ingredients
affect foam volume and stability
8/1/2012
Curds and Whey
8/1/2012
Curds and Whey
TEKS (6) The student studies the chemical
properties of food. The student is
expected to:
• (H) Analyze the occurrence of specific
chemical reactions
• (I) Analyze chemical and physical changes
in food
8/1/2012
Curds and Whey
Objective: The student will generate a
physical change of a substance from a
liquid state to a solid state
8/1/2012
Curds and Whey
The two major milk proteins are casein and whey.
When milk is acidified to a pH of 4.6 casein
becomes insoluble precipitating out of solution
forming curds.
Whey proteins remain soluble (do not denature) at
low pH and are found in the liquid that is
separated from the solid curds.
8/1/2012
Curds and Whey
• Casein exist in milk in the form of soluble
micelles.
• Casein consists of three primary forms
– Alpha, beta and kappa
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•
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Some portions of the micelle are
hydrophillic others are hydrophobic.
Colloidal CaPO4 is within the micelle.
Curds and Whey
• When pH is 4.6 or lower
• Colloidal CaPO4 within the micelle is
disrupted and micelle structure changes
• The micelle is no longer soluble
• The casein proteins then aggregate
forming a gel
8/1/2012
Curds and Whey
• Cheese making - rennet (chymosin and
pepsin, two enzymes) is used
• Kappa casein is cleaved from the casein
molecule
• Micelles are destabilized losing solubility
• Casein proteins aggregate forming a gel
(curds)
8/1/2012
Chemical Leavening
8/1/2012
Chemical Leavening
TEKS (6) The student studies the chemical
properties of food. The student is
expected to:
• (H) Analyze the occurrence of specific
chemical reactions
• (I) Analyze chemical and physical changes
in food
8/1/2012
(10) The student discusses how leavening agents are used in
baking. The student is expected to:
•
•
•
•
8/1/2012
(A) describe the purpose of leavening agents in baked
goods.
(B) Identify and describe major leavening agents.
(C) explain why baking soda is used with an acid in
baked goods
(F) discuss how air and steam act as leavening agents
Chemical Leavening
Objective: The student will assess the
effectiveness of various types of
leavening systems.
8/1/2012
Chemical Leavening
Chemical leavening systems consist of a
leavening agent (produces CO2 gas) and a
leavening acid (provides H+ ions that
cause the release of CO2)
8/1/2012
Chemical Leavening
• Common leavening agent
– Sodium bicarbonate or “baking soda”
(NaHCO3)
•
Common leavening acids
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Acetic acid (vinegar)
Lactic acid
Sodium aluminum sulfate
Monocalcium phosphate
Chemical Leavening
• Baking powder contains
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Sodium bicarbonate (leavening agent)
Sodium aluminum sulfate (leavening acid)
Monocalcium phosphate (leavening acid)
“Double acting” baking powder
Chemical Leavening
Leavening reaction in an aqueous system:
HCO3- + H+
H2CO3
H2O + CO2
Equilibrium is pH-dependent
8/1/2012
Chemical Leavening
Carbonic acid-bicarbonate equilibrium
H2CO3
HCO3- + H+ pKa = 6.35
Thus, below pH 6.35 bicarbonate is converted to
carbonic acid which in an aqueous system can
produce CO2 and water.
8/1/2012
Browning Reactions:
Maillard Reaction,
Caramelization,
and
Enzymatic Browning
8/1/2012
Browning Reactions - The Maillard Reaction (nonEnzymatic), Caramelization and Enzymatic
Browning
TEKS (6) The student studies the chemical property
of foods. The student is expected to:
• (H) analyze the specific occurrence of specific
chemical reactions.
• (I) analyze chemical and physical changes in
foods.
8/1/2012
Browning Reactions - The Maillard Reaction (nonEnzymatic), Caramelization and Enzymatic
Browning
TEKS (8) Student understands the functions of
enzymes. The student is expected to:
• (A) describe how enzymes act as catalysts.
• (D) identify factors that affect enzyme activity.
• (E) explain how enzyme reactions are involved
in food preparation.
8/1/2012
Browning Reactions - The Maillard Reaction
(non-Enzymatic), Caramelization and
Enzymatic Browning
TEKS (18) The student describes the
properties of proteins and amino acids.
The student is expected to:
• (C) explain what happens during
denaturation of protein and how the
process occurs.
8/1/2012
Browning Reactions - The Maillard Reaction
(Non-Enzymatic), Caramelization and
Enzymatic Browning
Objective: The student will summarize the
browning reactions.
8/1/2012
The Maillard Reaction (Non-Enzymatic)
Substrates:
Amino acids
+ Reducing sugars
Products:
Brown pigments + Flavor and odor compounds
Reaction is favored by:
•
higher pH’s (add baking soda)
•
intermediate water activity
8/1/2012
The Maillard Reaction (Non-Enzymatic)
“In other words”
Amino acids
(Amine groups)
-NH2
8/1/2012
+
Reducing sugars
(Carbonyl groups)
H
|
- C = O or – C = O
|
|
Amadori rearrangement
N-substituted glycosylamine
ketosamines
aldehydes + ketones
(flavor and odor compounds)
+ Melanodin pigments
(Brown pigments)
8/1/2012
•
Responsible for browning and flavor in:
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8/1/2012
Roasted coffee
Cooked meat
Sautéed onions
•
Sugars vary in their reactivity (most to least
reactive):
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Five-carbon sugars – xylose, arabinose
Six-carbon aldoses – glucose, galactose
Six- carbon ketoses – fructose
Reducing disaccharides – lactose, maltose
Non-reducing disaccharide – sucrose (non-reactive)
Caramelization
Heating and dehydration of sugars to produce brown
pigments and flavor compounds
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•
8/1/2012
Sucrose melts (160°C) and undergoes pyrolysis
Sucrose (C12)
Glucose (C6) + Fructose (C6)
Simple sugars condensation and undergo
dehydration forming large brown polymers
Caramelization
•
Examples of large brown polymers that form as
reaction progresses:
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Caramelan (C24)
Caramelen (C36)
Caramelin (C125)
Caramelization
Flavor compounds:
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•
•
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8/1/2012
Diacetyl ( 2,3-butanedione) important flavor
compound, produced during the first stages of
caramelization. Diacetyl produces a buttery or
butterscotch flavor
Esters and lactones - sweet rum-like flavor
Furans - nutty flavor
Maltol - toasty flavor
Caramelization
•
Reaction is responsible for flavor and aroma of:
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8/1/2012
Caramel candy
Syrups
Enzymatic Browning
Reaction catalyzed by the enzyme polyphenol
oxidase
Polyphenol
oxidase
+ O2
Phenols
8/1/2012
Melanin
Pigments
Enzymatic Browning
Responsible for browning in:
• Sliced bananas, apples, avocados, potatoes
• Dried fruit and vegetables
• Shrimp, crab, lobster
8/1/2012
Enzymatic Browning
Control reaction by:
• Denaturing enzyme
• Excluding oxygen
8/1/2012
Enzymatic Browning
Enzyme denaturation:
• Unfolding of protein structure
• Enzyme looses activity when denatured
8/1/2012
Enzymatic Browning
Enzyme denaturation caused by:
• pH extremes (add acids)
• Heat (blanching)
• Mechanical denaturation (whipping, beating,
kneading)
• Many others
8/1/2012
Have fun with the science of
food!
8/1/2012