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• 1 Prior knowledge - Physics

• 1.1 Interactions in Food Systems

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• What colloidal interaction can occur in food systems?

  • Electrostatic repulsion and attraction
    
  • Van der Waals interaction
  • Hydrogen bonds
  • Hydrophobic interactions
  • Salt bridges
  • Steric repulsions and bridging interactions
  • Depletion interaction

• What is the DLVO theory?

  The total interaction is the repulsive interaction + attractive interaction. The repulsive interaction are electrostatic repulsions, dependent pH and salt content. The attractive interaction are van der Waals interactions, independent on pH and salt content.

• What salt concentrations are needed for a secondary minimum?

  High salt concentrations

• What happens to the DLVO potential when adding salt?

  • Low amount of salt --> DLVO potential attractive, primary minimum 
    
  • Higher salt --> range of the repulsion is reduced. Van der  Waals (attractive) contribution to the DLVO potential becomes more important, secondary minimum (very weak attraction)
  • Even higher salt --> repulsion weaker, DLVO potential dominated by attractive van der Waals potential, primary minimum

• When are hydrogen bonds formed?

  A slightly negatively charged oxygen atom and a slightly positively charged hydrogen atom.

• How do inter- and intramolecular hydrogen bonds influence structure and solubility?

  Inter --> between different molecules. Water molecules are able to form a hydration layer around colloidal particles that carry hydrophilic groups. Additional short-ranged repulsive interaction between hydrophilic groups. 
  
  Intra --> form between 2 groups of the same molecule, e.g. Double helix of DNA
  
  
  Hydrogen bonds --> solubility higher 

• What is the hydrophobic effect?

  When a non-polar molecule is introduced in water, the water molecules next to the apolar molecule are not able to partake fully in the network of hydrogen bonds. This is an unfavourable situation. In order to minimise the contact between the water molecules and the apolar residues of the molecules, the apolar molecules tend to cluster.

• Why are hydrophobic interactions important in food?

  They are responsible for the structure of globular proteins, as the hydrophobic interactions keep the more hydrophobic protein groups within the core of the globular proteins.

• How are hydrogen bonds and hydrophobic interactions dependent on temperature?

  
  Temperature higherHydrogen bonds --> weaker
  Hydrophobic interactions --> stronger

• When are salt bridges formed?

  Multi-valent ions may form weak bonds between different macromolecules that carry a charge that is opposite of sign.