Structure function relation

Question 1

What is the link between what we know about the protein and what we want to know about the protein?

Answer 1

What we need to know about the protein –> molecular properties.

Question 2

Proteins isolates from a similar source do not have the same composition and functionality. TRUE OR FALSE?

Answer 2

TRUE

Question 3

Say three molecular properties, base on … and affected by…

Answer 3

• Charge: based on polar charged AA, affected by pH, chemical modification (Maillard).
• Hydrophobicity: based on hydrophobic AA, affected by unfolding(temperature, SDS, urea) hydrolysis.
• Polarity: based on polar charged/ non charged AA, does not have any parameters that affects the polarity.
• Disulfide bridges: based on cysteine that can make bridges within the protein and also links between different types of proteins and thereby make a gel. Affected by alkaline pH and temperature.

Question 4

Link between technical properties and molecular properties: and give three examples.

Answer 4

Identify underlying mechanism.
Examples:
1. Function: solubility, Underlying mechanism: interaction with water/with other proteins, Molecular properties: hydrophobicity, charge. Food: beverages.
2. Function :emulsification/foaming, Underlying mechanism: adsorption kinetics, stabilisation of the interface, Molecular properties: charge, hydrophobicity, Food: ice cream, salad dressings.
3. Function: gelation, Underlying mechanism: unfolding, aggregation , Molecular properties: size, charge, hydrophobicity, structure, disulfide bridges, Food: meat products, pasta, candy.

Question 5

Difference in foam ability of B-lactoglobulin and ovalbumin: EXAMPLE explain.

Answer 5

• Function: B-lactoglobulin makes a good foam and ovalbumin no.
• Underlying mechanism: we see the surface pressure for beta-lactoglobulin increases very quickly as a function of time and ovalbumin does not.
• Molecular properties: most of the properties are similar, but there is a very big difference in the hydrophobic exposure groups. B-lactoglobulin has a higher hydrophobicity, that is reflected in the fast adsorption kinetics that is reflected in a better foaming ability.

Question 6

EXAMPLE: foam stability of heated lysozyme. Explain.

Answer 6

Function: The longer heated lysozyme makes a much more stable foam.
Underlying mechanism: measure the surface pressure, you see that all the samples have a similar kinetics of adsorption and also reach the same final surface pressure. In many cases the underlying mechanism is still unclear.

Question 7

Describe which techno-functional properties are mostly affected by heating of a protein and explain which molecular properties are responsible for this.

Answer 7

Molecular properties: hydrophobicity, size, disulfide bridges and structure.
Techno-functional properties: solubility, viscosity, gelation, emulsification/foaming , fat and flavour binding.

Question 8

Methods to increase the exposed hydrophobicity? For globular proteins.

Answer 8

• Covalent coupling of fatty acids ( succinylation and lipophilization).
• By (partial) unfolding–> (partial) hydrolysis

Question 9

Methods to increase the total electrostatic repulsion between proteins?

Answer 9

1- pH, closer to pI less total net charge, less repulsion.
2- Higher ionic strength (salt concentration) will result in less repulsion.
3- Maillard reaction will result in loss of the free amino groups (positively charged at pH 7), so consequently will lead to increased total net charge.