Eggs

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Chapter 7

• Eggs

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Composition of eggs
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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)

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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

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Composition of Eggs -egg white (albumen)

• Proteins (contn)
• 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)

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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)

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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)

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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

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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

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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

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Functionality of Eggs

• Coagulation
• Emulsification
• Foaming

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Functionality of EggsCoagulation or Gelation
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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.

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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 ?

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Functionality of Eggs -coagulation

• Sugar decreases the rate of heat denaturation
  increases the coagulation temperature
• Salts promote coagulation

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Functionality of Eggs
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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

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Functionality of EggsFoaming
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Functionality of Eggs - foaming

• A colloidal suspension bubbles surrounded by egg
  albumen (protein)
• globulins have greater foaming ability
• ovomucin stabilizes the foam

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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

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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

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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

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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

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Functionality of Eggs
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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

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Functionality of Eggs
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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

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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

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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)

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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

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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)

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Proverbs 1215

• The Way of a Fool
• Seems right to Him
• BUT a Wise Man
• Listens to Advice