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VHTM > Egg > Flashcards

Egg Flashcards

1
Q

What are the types of proteins?

A
  1. Simple

2. Conjugated/complex proteins: composed of simple protein and non-protein material

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2
Q

What are the types of simple proteins?

A
  1. Globular = somewhat rounded in shape
    - Ovalbumin in egg whites
    - Lactalbumin and lactoglobulin in milk
    - Gliadin and glutenin in wheat
  2. Fibrous = coiled or extended in shape
    - Collagen and elastin in connective tissue of meat
    - Myosin in the muscle of meat
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3
Q

What are the types of complex proteins?

A
  1. Phosphoproteins (protein + phosphoric acid)
    - Casein proteins in milk
  2. Glycoproteins (protein + carbohydrate)
    - Ovomucin in eggs
  3. Lipoproteins (protein + fatty substance)
    - Lipoproteins in egg yolks and in whipping cream
  4. Chromoproteins (protein + coloured material)
    - Myoglobin in the muscle of meat
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4
Q

What is the protein structure?

A
  1. Primary: amino acids linked by peptide bonds (linkage/covalent bond) to form polypeptide chains
    - Very strong bonds and cannot be broken by normal cooking methods
  2. Secondary: spring-like coiling of polypeptide chain, usually into an alpha helix
    - Eg. simple fibrous proteins
  3. Tertiary: helix folds back on itself to form globular structure
    - Eg. simple globular proteins
  4. Quaternary: globular proteins combine with each other or non-protein substance
    - Eg. conjugated/complex proteins
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5
Q

What is the isoelectric point?

A
  • Carboxyl group donates H+
  • Amino group accepts H+ ions
  • The point where amino acid (a protein molecule) no longer has electrical charge
  • The like charges of protein are no longer repelling each other, which makes them unstable
  • Protein molecules are then attracted to each other and form hydrogen bonds with each other to create larger molecules
  • Proteins cannot stay in colloidal dispersion because like charges no longer repel as the proteins grow in size
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6
Q

What are the factors affecting proteins?

A
  1. pH - least stable at IEP
  2. Temperature
    - Partially increases due to cooking
    - Decreases (freezing)
  3. Mechanical action
    - Eg. beating of egg white
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7
Q

What do the factors affecting proteins result in?

A

Denaturation

Possibly coagulation, or over-coagulation

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8
Q

What is denaturation?

A

Change from the naturally ordered configuration (shape) of a protein molecule to a more randomly structured molecule

Hydrogen bonds are broken but NOT peptide bonds

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9
Q

What is coagulation?

A
  • New hydrogen bonds at new locations among polypeptide chain (within protein molecule)
  • Not reforming the original hydrogen bonds
  • Cause is the same or different from cause of denaturation
  • Most common cause is heat (continuing heat, initially would cause denaturation)
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10
Q

What is over-coagulation?

A

Result due to prolonged exposure to:

  • pH change (normally a decrease in pH)
  • Heat (too high or too long)
  • Mechanical action (least likely)
  • Polypeptide chains compress together and squeeze out water because excess hydrogen bonds form
  • Syneresis occurs in a GEL
  • Curdling occurs in a SOL (cannot happen in starch because proteins are having excessive hydrogen bonds)
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11
Q

What are the functional properties of eggs?

A
  1. Thickeners - SOL forms
  2. Gelling agents - GEL forms
  3. Foaming agents - egg whites only
  4. Emulsifiers - lecithin in egg yolks only
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12
Q

What are the factors affecting coagulation of egg proteins?

A
  1. Temperature
    - Egg white proteins: coagulation is 62-65 C, overcoagulation is 70 C
    - Egg yolk proteins: coagulation is 65-70 C, overcoagulation is 75 C
  2. Amount (quantity) of egg proteins
    - Diluting egg solution with water, milk, or fruit juices in recipes keep egg proteins further apart
    - Higher temperature needed for denaturation and coagulation because they are further apart
    - A dilute solution results in a less thick SOL or a less firm GEL
  3. Sugar
    - Forms hydrogen bonds with egg proteins resulting in a slower rate of denaturation and coagulation
    - Results in an increase in coagulation
    - Decrease SOL thickness or GEL firmness
    - Sugar reduces bonding between the actual egg proteins
    - Helps protect against over-coagulation of
    egg proteins
    - Less chance of curdling in a SOL
    - Less chance of syneresis in a GEL
  4. Acids
    - Contributes H+ ions which neutralize negative charges around egg protein molecules
    - Stablizing factor in eggs is the negative charges repeling
    - Egg proteins reach IEP and denature and coagulate faster
    - Results in decrease in denaturation and coagulation temperatures (unstable)
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13
Q

How do you prevent over-coagulation?

A

Generally preventing over-heating is a good method

  • Use double boiler (top of stove)
  • Use oven poaching (in the oven)
  • Keep temperatures higher or equal to boiling temperature (100 C)
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14
Q

What occurs during the storage of eggs?

A
  • Fresh egg broken onto flat plate stands up in rounded form due to viscosity of
    thick portion of egg white
  • As eggs age/deteriorate, amount of thin egg white increases
  • Lose moisture which cause air cell between two membranes to enlarge
  • Lose carbon dioxide which causes egg white to become alkaline, and thin out
  • Egg yolk absorbs water from egg white and yolk membrane stretches
  • When broken onto plate, deteriorated egg yolk flattens and whole egg
    spreads
  • Chalazae disintegrates and doesn’t hold yolk in place at the center
  • Eggs should be refrigerated to retain quality for 2 weeks
  • Kept in original carton to prevent moisture loss and absorption of
    odours
  • Porous shell allows absorption of strong odours (onions, apples, citrus
    fruits, cabbage, cheese)
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15
Q

What is the composition of egg yolk?

A
  • ½ water and ½ solid
  • Solids are 1/3 protein and 2/3 fat
  • Yolk contains lecithin for emulsifying properties
  • Contains cholesterol
  • No carbohydrate
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16
Q

What is the composition of egg white?

A
  • Contain more water and are less concentrated than yolk
  • Protein is main constituent
  • Proteins called albumins account for 80% of protein
  • Egg white can be called egg albumin
  • Readily coagulated by heat
  • Almost no fat or carbohydrate
  • Mineral and vitamin content is lower than yolk
17
Q

What is egg white foam?

A

Colloidal dispersion in which air bubbles (dispersed phase) are trapped in a liquid (continuous phase)

18
Q

What does beating egg whites do?

A
  • Incorporates air bubbles into the liquid portion of egg whites
  • Denatures egg white proteins which collect on surface of egg white bubble
  • Stabilizes foam (longer time before foam collapses)
19
Q

What does baking egg white foam do?

A

Causes egg proteins to coagulate to make form permanent (will never collapse over time)

20
Q

What are the factors affecting egg white foam quality (volume and stability)?

A
  • Age of eggs
  • Temperature
  • Length of beating
  • Sugar
  • Acid
  • Fat
21
Q

How does age of eggs affect egg white foam quality?

A
  • Fresh eggs produce higher foam
  • Eggs greater than 10 days old produce lower volume
  • Maximum volume comes from eggs that are 2-3 days old
22
Q

How does temperature of eggs affect egg white foam quality?

A

Room temperature (15-25 C) produces largest volume of egg white foam

23
Q

How does length of beating affect egg white foam quality?

A
  • Under beating means too few egg white proteins are denatured = less stable foam which collapses faster
  • Overbeating causes the denatured proteins to be less flexible and the air cells begin to break = lower foam volume, less stable
24
Q

How does sugar affect egg white foam quality?

A
  • Forms hydrogen bonds with egg white proteins, interfering with denaturation
  • If sugar is added at the start of beating, the time required to create foam increases and foam volume will be reduced
  • If sugar added at soft peak stage, you will get a more stable foam (stiff) to prevent over-coagulation
25
Q

How does acid affect egg white foam quality?

A
  • Eg. lemon juice, vinegar, or dry acid salt like cream of tartar
  • Creates more stable, larger volume and stiffer foams
  • H+ neutralize negative charges around egg white protein molecules
  • Egg white proteins reach IEP and denature faster
  • The more denatured proteins, the more stable the foam
  • Always added at beginning of beating so foam forms faster
26
Q

How does fat affect egg white foam quality? What should you do?

A
  • Delays or prevents foam formation
  • 0.1% of egg yolk prevents foam formation
  • Egg yolk solids contain 67% fat
  • Lipoproteins in egg yolks form complex with egg white proteins preventing denaturation
  • Use glass or metal bowl, not plastic/silicone to beat egg whites (fat adheres to plastic so if you’ve baked with it before it stays)
27
Q

What is the emulsifier in egg?

A
  • Lecithin in egg yolks is an emulsifier
  • Lecithin has hydrophilic and hydrophobic ends to bond to water/fat
  • Keeps immiscible liquids from separation
28
Q

Explain the cause of the grey-green colour in hard-boiled and scrambled eggs.

A
  • Hydrogen sulfide (H₂S) in egg white combines with iron in egg yolk
  • Forms ferrous sulfide (FeS₂) which has a grey-green colour

Hard boiled:
- Slow cooling after cooking, pressure of heat allows contact between egg white and yolk (allows hydrogen sulfide and iron to react)

Scrambled:

  • Keep eggs hot for too long after cooking/after proteins have coagulated allows compounds to move around
  • Iron in yolk and hydrogen sulfide in white come into contact while still warm for long period of time
29
Q

Explain the solution to prevent the grey-green colour in hard-boiled and scrambled eggs.

A

Hard boiled:

  • Cool rapidly in cold water
  • Reduces pressure on outside of egg drawing hydrogen sulfide in egg white from yolk
  • Crack eggs to remove shell to remove pressure

Scrambled:
- Prepare in small batches, limiting heating time, minimize heat

The longer the egg proteins are heated after coagulation, the more grey-green ring and also over-coagulation will occur (tough texture due to over-coagulation of proteins)

30
Q

Can you freeze and thaw egg whites/egg yolks?

A

Whites:

  • Raw, yes
  • Cooked, no (tough and rubbery)

Yolks:

  • Raw, no (proteins denature = thick and gummy)
  • Cooked, yes
  • If you add sugar or salt to raw yolk before freezing, it is fine because proteins are protected

VHTM (12 decks)

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