Introduction - Effects of heating and processing

8 important questions on Introduction - Effects of heating and processing

What are reasons to heat protein preparations?

- Inactivation of bacteria (and spores) and enzymes (endogenous enzymes: proteases, polyphenol -oxidases, protease inhibitors)
- Product modification; e.g. increased gelling properties

What are the effects of heating on protein preparations?

- Chemical modifications
  • Maillard reactions (more in dry state)
  • Cross-link reactions
    • disulfide bridge shuffling
    • formation of LAL/LAN
  • Dephosphorylation (caseins)
- Physical changes
  • Denaturation (globular proteins)
  • Dissocation (micellar proteins)
  • Precipitation of Ca-phosphate (caseins)

What happens to globular proteins (whey proteins) when they are heated?

It can result in aggregation. This is caused by unfolding, the hydrophobic patches become more exposed, there is an increase in hydrophobic attraction between the proteins. The aggregates can be soluble or insoluble.

What happens to micellar proteins (caseins) when they are heated?

Dissociation. First all the hydrophobic tails are put together in the middle of the micelle and all the hydrophilic groups are on the outside. By dissociation they become loose. When cooled down, the process can be reversed and the micelle can be restored.

What is the effect of heating on a casein macro-micelle?

It can disrupt the structure (small micelles of alpha s1, beta caseins and other caseins that are clustered together with calcium phosphate that binds the micelles together, on the outside the k-caseins), which results in dissociation of the complexes. This causes loose complexes in the solvent. Calcium phosphate looses interaction with the caseins. When you cool down, the calcium phosphate will partially precipitate, the micelles will reform but don't have the same structures as before the heat treatment (irreversible process).

What are 2 techniques to measure protein unfolding (whey protein)?

  1. Differential scanning calorimetry (DSC)
  2. Precipitation at pI

How does precipitation at iso-electric point work?

Look at the solubility, or transmittance, turbidity of samples.
  • A high solubility is observed for whey proteins at all pH values. At pI a small dip, but still proteins are quite soluble and have a high transmittance.
  • Heating for 1 min, around pI much lower solubility. Heating longer even lower values.
  • Solubility at pI can be used to quantify the amount of remaining native proteins.

What happens with proteins in spray drying?

While heating the sample (small droplets), we evaporate water. This costs energy, so it cools down the droplets and cools down the product. Water content in droplets decreases, water content in sample decreases, the denaturation temperature is increased.

Don't need to have denaturation during spray drying, because you make sure the water activity is lower when the temperature of the product becomes higher.

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