Emulsions in food systems

Question 1

Stability of emulsions: what can change the electrostatic interactions of the emulsions ?

Answer 1

1. pH: emulsions are okay because they are repeled by electrostatic repulsions. If we change the pH we see that the emulsions close to the pI becomes flocculated. This results in creaming and this is called destabilization. If you away from the pI , the systems becomes stable again. If i change the pH, i change the charge of the protein, next to pI no repulsion.
2. Ionic strength: if you add sodium chloride NaCl, to an emulsion at pH 7, we see destabilization. High ionic strength i do not have repulsion and i have flocculation.

Question 2

EMULSIONS FLOCCULATION:

Answer 2

Protein stabilised emulsions flocculate at the iso-electric point of the protein. The oil droplets starts to cluster together, at some point these larger clusters will cream to the top of the emulsion , leading to phase separation.

Question 3

Stabilisation of emulsions can be also stabilised by:

1. Electrostatic repulsion.
2. …………………………………….:

Answer 3

2. Steric repulsion: modification by oligosaccharides. Interaction with polysaccharides. At high ionic strength the system becomes stable against flocculation . The larger the oligosaccharide, the more distance between particles, and more stable against flocculation.

Question 4

Effect of charged polysaccharides on emulsion stability. Comparison of emulsions stabilised by: FIGURE 56.
Pure protein – Whey protein isolate (WPI)
Polysaccharide – Gum arabic (GA)
Algae soluble protein isolate (ASPI)

Answer 4

• Gum arabic does not have a pH dependet flocculation. No see a zero charge point.
  *ASPI, protein isolate that have similar behavior than the gum arabic. No see a zero charge point.
  *WPI: ph=pI, flocculation, we can se that the charge goes through zero around the isoelectric point.
  LOOK COMPOSITION: Non-protein compounds can have very significant effects on functionality

Question 5

A large variation in emulsion droplet size for 32 whey protein concentrates is observed. Describe and discuss 2 differences in the sample properties and how they would be induced in the product.

Answer 5

A large variation in emulsion droplet size for 32 whey protein concentrates is observed. Describe and discuss 2 differences in the sample properties and how they would be induced in the product.

1. During isolation different amounts of lipids (surfactants) remained in the product.
2. Different ratios of whey proteins are present.
3. The products were subjected to different heat treatments (pasteurisation / sterilisation / etc.), resulting in different states of unfolding / aggregation.
4. The samples were spray dried under different conditions, resulting in particles in the solution.