Foams and emulsions

Question 1

Similarities between foams and emulsions:

Answer 1

Mix system: oil on the top an water on the bottom with proteins in the solution. We shake, stir and the homogenize. The aim is to get the oil or the air dispersed in particles.

Question 2

Depending on the conditions:

Answer 2

• Stable
• No sufficient protein, make bigger bubbles–> coalescence.
• Depending on the pH or ionic strength we can get flocculation.

Question 3

To achieve a full adsorbed layer, depends on ?

Answer 3

1. This depends in how much oil you put in a system.
2. How much the concentration of the protein it is. Critical concentration for the minimum droplet size depends on adsorption rate, which in turn depends on charge and hydrophobicity.

Question 4

Understanding foams and emulsions:

• Function
• Underlying mechanism
• Molecular properties

Answer 4

• Function: foam/ emulsion (droplet/bubble size, foam/emulsion stability).
• Underlying mechanism: bubbles (drainage rate rupture) interface (adsorption kinetics, surface pressure).
• Molecular properties: solution: concentration, I, pH, type of protein, charge, hydrophobicity.

Question 5

What will happen with the foam and emulsion properties of ovalbumin if we apply a mild heat treatment ?

Answer 5

The protein unfolds, this will change the hydrophobicity. There for the adsorption kinetics (surface pressure vs. time) should be faster and more similar to B-lactoglobulin.
Foam formation will be better, foam stability higher. For the emulsion, the curve d3,2 vs. concentration will move to that of B-lactoglobulin.

Question 6

Adsorption kinetics of proteins depends on :

Answer 6

1. Hydrophobicity

2. Charge