Crystallization and matrix formation - Freezing and thatwing - Antifreeze proteins

4 important questions on Crystallization and matrix formation - Freezing and thatwing - Antifreeze proteins

What are antifreeze proteins and how does it work?

Proteins that inhibit the growth of ice crystals, by adsorbing on the ice-water interface. The molecules are folded such that they resemble ice crystals, not just in geometry but also in polarity. The proteins adhere to any ice surface, inhibiting the attachment of new water molecules, and hence effecting stopping the growth of the ice crystals.
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What is the main difference between using cryoprotectants and antifreeze proteins?

When cryoprotectants are used, the metabolism is stopped, it will only revive when they are thawed. When using antifreeze proteins, the metabolism still functions.
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What is the difference between using cryostabilizers and antifreeze proteins?

You need much less of the antifreeze proteins, 3-4 times less than when using a cryostabiliser.
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When using antifreeze proteins, the driving force to crystallize is still present, there is only kinetic inhibition. What does this mean?

  • If sufficient nuclei are present (lowering T too much) --> not sufficient antifreeze proteins present --> crystallisation will still happen
  • Only crystal growth is inhibited. Other collapse processes, such as oxidation, or enzymatic browning may still take place, since the matrix in this case is certainly in the rubbery (WLF kinetics) zone. Hence it will be susceptible to collapse phenomena.
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