Egg proteins

Question 1

List the egg proteins. [5]

Answer 1

• Ovalbumin
• Ovotransferrin
• Ovomucoid
• Lipovitellin
• HEWL

Question 2

Describe the distribution of egg proteins in an egg.

Answer 2

• Yolk contains more fat and protein than the albumen.

Question 3

Describe the egg white proteins.

Answer 3

• Lysozyme & Avidin (pI > 10) → Positively charged at pH 7
• Other Egg White Proteins (pI < 7) → Negatively charged at pH 7

Question 4

Of the egg white proteins, which are allergens?

Answer 4

Ovomucoid is the main allergen; ovalbumin is a major allergen

Note they are glycosylated except for lysozyme.

Question 5

Lysozyme is glycosylated.
True or False?

Answer 5

False.

Question 6

Lysozyme is not glycosylated.
True or False?

Answer 6

True.

Question 7

Describe ovalbumin.

Answer 7

• 58% of total protein
• Major allergen
• N-glycosylated: Asn-X-Thr/Ser
• 6 Cys - 1 disulfide
• SerP 87; SerP 350

Question 8

Describe ovotransferrin.

Answer 8

• 13% of total protein
• 30 Cys; 15 disulfides
• Binds Fe^3+; Mn^3+; or Cu^2+
• Stabilized Tm ~84 degrees C
• Without metals Tm ~63 degrees C

Question 9

Describe ovomucoid.

Answer 9

• Three domains; 186 aa total
• 18 Cys; 9 disulfides
• 5-6 glycosylation sites: Asn-X-Thr/Ser
• Primary egg allergen

Question 10

Describe lysozyme.

Answer 10

• First (useful) enzyme structure (1965)
• Cleaves peptidoglycan
• Antimicrobial activity
• 4 disulfide bonds
• In humans: saliva; tears; milk; mucus

Question 11

Rare mutations in human lysozyme lead to […]

Answer 11

Protein misfolding disease

Question 12

Describe the composition of the egg yolk.

Answer 12

Question 13

Describe high-density lipoproteins found in eggs.

Answer 13

• Globular structure
• 80% protein and 20% lipid (phospholipids and TAGs)

Egg yolk.

Question 14

What are the main three functions that egg proteins provide in food systems?

Answer 14

• Gelation (albumen; albumen + yolk)
• Foaming (albumen)
• Emulsification (mainly yolk = phospholipids; lipoprotein)

Question 15

Describe how egg proteins contribute to foaming.

Answer 15

• Calcium binding: stabilizes ovotransferrin; limits denaturation
  
  • Update: silver bowl works - ovotransferrin doesn’t bind Ag
  • New idea: metals stabilize -SH groups; prevent cross-linking

Question 16

Describe the differences in egg foam after various methods and beating times.

Answer 16

✅ Low pH (acidic stabilizers like cream of tartar, lemon juice) →
* Keeps -SH protonated, delaying disulfide bond formation, preventing overcoagulation, but making the foam initially weaker.

✅ Higher pH →
* -SH deprotonates (-S⁻), allowing disulfide bonds to form, strengthening the foam structure.

✅ Copper bowls stabilize egg foams →
* React with ovotransferrin (conalbumin) to strengthen the foam.
* Bind -SH groups, preventing premature disulfide bonds, leading to a finer, stronger foam.
* Mimics acid stabilizers but provides better control and delays overbeating.

✅ Stainless steel bowls are neutral →
* Do not stabilize foams, so acid stabilizers are required for better structure.

Keeping SH protonated prevents disulfide bond formation, leading to a less stable foam with weaker protein interactions.

Question 17

Describe recombinant egg white proteins.

Answer 17

• Animal free egg white protein

Question 18

Can ‘plant-based eggs’ be successful?

Answer 18

• Flavour may be okay - functionality is not!