Chapter 7
Eggs
Composition of eggs
% W ater Pro tein Fat CHO
W h o le 100 7 4,6 1 2, 1 11,2 1, 2
W h ite 58 8 8,0 1 0, 1 0,2 0,8
Yolk 31 4 8,0 1 6,4 32,9 2,0
Composition of Eggs -
egg white (albumen)
? Water (~88%)
? CHO (~1%)
?mainly glucose,may cause brown
discoloration in dried eggs and hard cooked
eggs (Millard reaction)
? Fat (trace)
Composition of Eggs -
egg white (albumen)
? Proteins (~11%),most are glycoproteins
?Three primary proteins,
? ovalbumin (54%) Structure of Baked Products
ovotransferrin (12%),Binds metal,Discoloration
ovomucoid (11%) Protease Inhibitor
? ovomucin (1.5%),A Fibrous Protein,
contributes to the thickness of the white (4 x
more abundant than in yolk),contributes to
the stability of egg white foam
Composition of Eggs -
egg white (albumen)
? Proteins (cont’n)
?globulins (8%),including lysozyme,are
important for foaming
?lysozyme,ability to hydrolyze a
polysaccharide in the cell wall of some
bacteria to prevent bacterial spoilage
? others,ovoinhibitor,ovoflavoprotein,
ovomicroglobulin,avidin (binds biotin,but is
heat sensitive)
Composition of Eggs -
egg yolk
? Proteins (16.4%),
? plasma (78%),livetin & LDL (protein
content ~ 10%)
? granular fraction,phosvitin (16%,
carrier of Fe),lipovitellins (70%) & LDL
(12%)
? Water (48%)
Composition of Eggs -
egg yolk
?Lipids (32 to 34%)
? triglycerol (66%)
? phospholipid (28%) including lecithin
? (has remarkable emulsifying ability)
? cholesterol (3%,or 250 mg)
?The color of yolk depends on the
presence of carotenoids.
? xanthophylls not carotene
(Lutein and zeaxanthin)
Egg Quality
? Commercial grading of eggs according
to the USDA standards
? External quality,shell characteristics,
shape,soundness,cleanliness,& color
? Interior quality,size of the air cell,
firmness of the white,& the yolk
(distinct or flattened during aging)
? Evaluated by candling
Egg quality during storage
? The size of the air cell increases
? water evaporates from the egg through shell
? The egg white becomes thinner
? ovomucin undergoes degradation
? pH of white increases (from ~ 8 to ~9)
? due to the loss of CO2 through the pores
Egg quality during storage
?The yolk enlarges and the membrane weakens
(water moves from white to yolk,viscosity decreases,
yolk becomes flatter and spreads farther)
? Deterioration of odor & flavor
? Increased storage temperature accelerates loss of
quality
Functionality of Eggs
?Coagulation
?Emulsification
?Foaming
Functionality of Eggs:
Coagulation or Gelation
Protein Coagulation
? Denaturation,Relaxation of the tertiary
structure to the secondary structure,
accompanied by decreasing solubility of a
protein
? Precipitation of protein as molecules
aggregate (often as a result of energy
input,such as heating or beating)
? Process that results in a loss of solubility
or a change from a fluid state to a solid
state,(Gelation is also used to describe
the process.
Functionality of Eggs -
coagulation
?egg white begins to thicken at
~62oC,yolk at ~65oC,72oC Firm
? The gel firmness depends on time &
temperature of heating
? Gel hardness dependents on the pH
and the concentration of protein
? increased pH or protein will increase gel
hardness
? diluted protein will increase coagulation
temperature ∟
Functionality of Eggs -
coagulation
? Sugar decreases the rate of heat
denaturation & increases the
coagulation temperature
? Salts promote coagulation
Functionality of Eggs
Functionality of Eggs -
emulsification
? Formation of emulsion
? mechanical agitation makes it
insoluble and stiff or stable
? emulsifying agent (Lecithin)
? Egg Yolk is an oil-in-water
emulsion
Functionality of Eggs:
Foaming
Functionality of Eggs -
foaming
? A colloidal suspension,bubbles
surrounded by egg albumen (protein)
? globulins have greater foaming
ability
? ovomucin stabilizes the foam
Functionality of Eggs -
factors affecting foaming
? Method,time and temperature of
beating
? as beating time increases,volume and
stability of the foam 1st increases then
decreases
? maximum stability is reached before
maximum volume
? room temperature vs refrigerator
temperature
Functionality of Eggs -
factors affecting foaming
? Characteristics of the egg white
? thin white vs thick white
? stored eggs vs fresh eggs
? pH
? acids or acid salts increases foam
stability but delays foam formation
Functionality of Eggs -
factors affecting foaming
? Water
? water increases the foam volume but
decreases its stability
? fat
? oil reduces foam volume
? sodium chloride
? reduces the foam stability,increases
whipping time
Functionality of Eggs -
factors affecting foaming
? Sucrose
? delays foam formation (so beat then add)
? produces a more stable foam
? egg yolk
? decreases the foam volume
? additives
? surfactants and stabilizers may reduce
whipping time,increase foam volume
Functionality of Eggs
Functionality of Eggs -
factors affecting foaming
? Method,time and temperature of
beating
? characteristics of the egg white
? pH
? water and fat
? sodium chloride
? sucrose
? egg yolk
? additives
Functionality of Eggs
Processed Eggs
? Frozen eggs
? egg whites perform well after freezing &
thawing
? add 10% (w/w) of sugar or salt to yolks
before freezing to control the gelation
of frozen yolk
? To prevent,syneresis” in frozen cooked
egg products:
? addition of gums
? addition of citric acid
? addition of salt
Processed Eggs
? Egg substitutes
? use of egg white together with a yolk-
like mixture containing no cholesterol
? fortify with fat-soluble nutrients
? addition of carotenoid for giving the
yolk color
? addition of carboxymethyl-cellulose
(CMC) reduces weeping
? aroma and flavor are not as good as
fresh eggs
Processed Eggs
? Dried eggs (spray drying)
? products,whole-egg solids,yolk solids,
fortified whole-egg solids and whites
? growth of microorganisms is inhibited
? coagulation is not affected
? foaming potential is reduced
? add whipping agents (surface active)
Processed Eggs
? All liquid eggs should be
pasteurized (61C for 3.5 min) to
kill salmonella and other potential
pathogens.
? Ultrapaseurized liquid whole eggs
? retain functional properties of fresh
shell eggs
? are aseptically packaged
Functionality of Eggs,
Summary
? coloring agent (carotenoids in yolk)
? emulsifier
?mayonnaise,hollandaise sauce,cream puff
? thickening agent (coagulation)
? baked (gel) or stirred (sol) custards,
? foaming
? meringues,foam cakes (angel,sponge,
and chiffon)
Proverbs 12:15
The Way of a Fool
Seems right to Him
BUT a Wise Man
Listens to Advice
Eggs
Composition of eggs
% W ater Pro tein Fat CHO
W h o le 100 7 4,6 1 2, 1 11,2 1, 2
W h ite 58 8 8,0 1 0, 1 0,2 0,8
Yolk 31 4 8,0 1 6,4 32,9 2,0
Composition of Eggs -
egg white (albumen)
? Water (~88%)
? CHO (~1%)
?mainly glucose,may cause brown
discoloration in dried eggs and hard cooked
eggs (Millard reaction)
? Fat (trace)
Composition of Eggs -
egg white (albumen)
? Proteins (~11%),most are glycoproteins
?Three primary proteins,
? ovalbumin (54%) Structure of Baked Products
ovotransferrin (12%),Binds metal,Discoloration
ovomucoid (11%) Protease Inhibitor
? ovomucin (1.5%),A Fibrous Protein,
contributes to the thickness of the white (4 x
more abundant than in yolk),contributes to
the stability of egg white foam
Composition of Eggs -
egg white (albumen)
? Proteins (cont’n)
?globulins (8%),including lysozyme,are
important for foaming
?lysozyme,ability to hydrolyze a
polysaccharide in the cell wall of some
bacteria to prevent bacterial spoilage
? others,ovoinhibitor,ovoflavoprotein,
ovomicroglobulin,avidin (binds biotin,but is
heat sensitive)
Composition of Eggs -
egg yolk
? Proteins (16.4%),
? plasma (78%),livetin & LDL (protein
content ~ 10%)
? granular fraction,phosvitin (16%,
carrier of Fe),lipovitellins (70%) & LDL
(12%)
? Water (48%)
Composition of Eggs -
egg yolk
?Lipids (32 to 34%)
? triglycerol (66%)
? phospholipid (28%) including lecithin
? (has remarkable emulsifying ability)
? cholesterol (3%,or 250 mg)
?The color of yolk depends on the
presence of carotenoids.
? xanthophylls not carotene
(Lutein and zeaxanthin)
Egg Quality
? Commercial grading of eggs according
to the USDA standards
? External quality,shell characteristics,
shape,soundness,cleanliness,& color
? Interior quality,size of the air cell,
firmness of the white,& the yolk
(distinct or flattened during aging)
? Evaluated by candling
Egg quality during storage
? The size of the air cell increases
? water evaporates from the egg through shell
? The egg white becomes thinner
? ovomucin undergoes degradation
? pH of white increases (from ~ 8 to ~9)
? due to the loss of CO2 through the pores
Egg quality during storage
?The yolk enlarges and the membrane weakens
(water moves from white to yolk,viscosity decreases,
yolk becomes flatter and spreads farther)
? Deterioration of odor & flavor
? Increased storage temperature accelerates loss of
quality
Functionality of Eggs
?Coagulation
?Emulsification
?Foaming
Functionality of Eggs:
Coagulation or Gelation
Protein Coagulation
? Denaturation,Relaxation of the tertiary
structure to the secondary structure,
accompanied by decreasing solubility of a
protein
? Precipitation of protein as molecules
aggregate (often as a result of energy
input,such as heating or beating)
? Process that results in a loss of solubility
or a change from a fluid state to a solid
state,(Gelation is also used to describe
the process.
Functionality of Eggs -
coagulation
?egg white begins to thicken at
~62oC,yolk at ~65oC,72oC Firm
? The gel firmness depends on time &
temperature of heating
? Gel hardness dependents on the pH
and the concentration of protein
? increased pH or protein will increase gel
hardness
? diluted protein will increase coagulation
temperature ∟
Functionality of Eggs -
coagulation
? Sugar decreases the rate of heat
denaturation & increases the
coagulation temperature
? Salts promote coagulation
Functionality of Eggs
Functionality of Eggs -
emulsification
? Formation of emulsion
? mechanical agitation makes it
insoluble and stiff or stable
? emulsifying agent (Lecithin)
? Egg Yolk is an oil-in-water
emulsion
Functionality of Eggs:
Foaming
Functionality of Eggs -
foaming
? A colloidal suspension,bubbles
surrounded by egg albumen (protein)
? globulins have greater foaming
ability
? ovomucin stabilizes the foam
Functionality of Eggs -
factors affecting foaming
? Method,time and temperature of
beating
? as beating time increases,volume and
stability of the foam 1st increases then
decreases
? maximum stability is reached before
maximum volume
? room temperature vs refrigerator
temperature
Functionality of Eggs -
factors affecting foaming
? Characteristics of the egg white
? thin white vs thick white
? stored eggs vs fresh eggs
? pH
? acids or acid salts increases foam
stability but delays foam formation
Functionality of Eggs -
factors affecting foaming
? Water
? water increases the foam volume but
decreases its stability
? fat
? oil reduces foam volume
? sodium chloride
? reduces the foam stability,increases
whipping time
Functionality of Eggs -
factors affecting foaming
? Sucrose
? delays foam formation (so beat then add)
? produces a more stable foam
? egg yolk
? decreases the foam volume
? additives
? surfactants and stabilizers may reduce
whipping time,increase foam volume
Functionality of Eggs
Functionality of Eggs -
factors affecting foaming
? Method,time and temperature of
beating
? characteristics of the egg white
? pH
? water and fat
? sodium chloride
? sucrose
? egg yolk
? additives
Functionality of Eggs
Processed Eggs
? Frozen eggs
? egg whites perform well after freezing &
thawing
? add 10% (w/w) of sugar or salt to yolks
before freezing to control the gelation
of frozen yolk
? To prevent,syneresis” in frozen cooked
egg products:
? addition of gums
? addition of citric acid
? addition of salt
Processed Eggs
? Egg substitutes
? use of egg white together with a yolk-
like mixture containing no cholesterol
? fortify with fat-soluble nutrients
? addition of carotenoid for giving the
yolk color
? addition of carboxymethyl-cellulose
(CMC) reduces weeping
? aroma and flavor are not as good as
fresh eggs
Processed Eggs
? Dried eggs (spray drying)
? products,whole-egg solids,yolk solids,
fortified whole-egg solids and whites
? growth of microorganisms is inhibited
? coagulation is not affected
? foaming potential is reduced
? add whipping agents (surface active)
Processed Eggs
? All liquid eggs should be
pasteurized (61C for 3.5 min) to
kill salmonella and other potential
pathogens.
? Ultrapaseurized liquid whole eggs
? retain functional properties of fresh
shell eggs
? are aseptically packaged
Functionality of Eggs,
Summary
? coloring agent (carotenoids in yolk)
? emulsifier
?mayonnaise,hollandaise sauce,cream puff
? thickening agent (coagulation)
? baked (gel) or stirred (sol) custards,
? foaming
? meringues,foam cakes (angel,sponge,
and chiffon)
Proverbs 12:15
The Way of a Fool
Seems right to Him
BUT a Wise Man
Listens to Advice
