Protein modifications - Heating: Changes in protein tertiary or quarternary structure

5 important questions on Protein modifications - Heating: Changes in protein tertiary or quarternary structure

Caseins cannot unfold, as they do not have a secondary or tertiary structure, however the native structure of the casein macro-micelle can be disrupted by heating, how do you call this and what happens then?

Dissocation. The calcium and phosphates that were present tin the micelles can release, as well as the individual molecules in the micelles. Some re-assocation (in the form of micelles) takes place after the heat is removed and the sample is cooled down.

The total extent of aggregation of globular proteins depends a lot on the conditions, such as?

  • Concentration. In highly diluted systems, the proteins will not meet each other frequently. Whereas in concentrated systems the collision frequency is much higher.
  • Electrostatic repulsion influences type of aggregates formed. Changing the pH of the solution, towards the pI --> aggregation can also occur when they are in their globular state, without unfolding.

What is the denaturation temperature?

The temperature at which 50% of the proteins are unfolded and 50% are in the native state. The proteins should be heated at least close or above this temperature to get significant effects of protein denaturation.
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What happens during spray-drying of proteins?

Done at high air temperatures, little or no protein denaturation takes place. Has to do with the balance between the denaturation temperature and the temperature of the sample. During spray drying, the protein solution is sprayed into a thin mist, where the water in each droplet evaporates in the hot air of the spray-dryer.
  1. Evaporation of water effectively cools down the droplet, slightly delaying the increase of temperature in the droplet
  2. As the water evaporates, the water activity in the droplet goes down, which results in an increase of denaturation temperature of the proteins

Why are there particle that do not dissolve after spray-drying of proteins?

Parts of the powder may be more 'heat damaged' than others. A certain percentage of the powder remains present as large aggregates, or even particle shells (of collapses powder particles). These can be removed by filtration or centrifugation since their size is much larger than that of the protein itself.

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