Dehydration Effect
Native protein is stabilized by the folding of hydrophobic chains
into the protein molecules and is held together by many other
forces, including hydrogen bonding, dipole–dipole interactions,
electrostatic interactions, and disulfite linkages (Benjakul and
Bauer 2000). The formation of ice during freezing removeswater
from the protein molecules, thus disrupting the hydrogen bonding
network between the native proteins and water molecules
and exposing the hydrophobic or hydrophilic sites of the protein
molecules (Shenouda 1980). The exposed hydrophobic or hydrophilic
sites of the protein molecules interact with each other
to form hydrophobic–hydrophobic and hydrophilic–hydrophilic
bonds, either within the protein molecules, resulting in deconformation
of the native three-dimensional structure of protein, or
between adjacent protein molecules, causing protein–protein interactions
and resulting in aggregation (Shenouda 1980). Xiong
(1997) proposed that protein aggregates to maintain its lowest
free energy as water forms ice, thus resulting in protein denaturation.
Matsumoto (1979) suggested that redistribution of
water during freezing allows protein molecules to move closer
together and aggregate through intermolecular interactions. Lim
and Haard (1984) found that the loss of protein solubility as a
result of protein denaturation in Greenland halibut during frozen
storage was mostly due to the noncovalent, hydrophobic interactions
in protein molecules. Buttkus (1970) proposed that the
formation of intermolecular S–S bonds is the major cause of
protein denaturation.
Solute Concentration Effect
As ice forms, the concentration of mineral salts and soluble
organic substances in the unfrozen matrix increases. As a result