Freezing Technology

5.1.1.6 Freeze Denaturation-I

Unfolding of molecules due to secondary reaction between the reactive groups of different proteins and other components of fish muscle, leading to cross linking and formation of aggregates

• The proteins lose part of their solubility and reduced enzyme activity
• As a result of these changes significant deterioration of the functional properties of the fish meat may occur
• It is manifested by a decrease in water retention, gel forming ability and lipid emulsifying capacity worsening of texture and the increased dryness of fish meat
• Fish that are stored for longer period becomes tough, chewy, rubber and fibrous
• Causative factors comprise the denaturing are

1. Catalytic effect of ice and inorganic salts

2. The binding of fatty acid

3. Lipid oxidation products

• Cross linking induced by formaldehyde generated in the muscle of some fish (Gadoid) results in the formation of new covalent bonds in denatured products
• Ice crystals disturb the hydrophobic interaction in protein. Increase in concentration of salt in unfrozen food and water decrease the hydration of protein as the concentrated inorganic ions compete for the water molecules
• They participate in freeze denaturation of protein by catalyzing the hydrolysis and auto oxidation of lipids
• Free fatty acid decrease the solubility of myofibrillar protein and contribute to the formation of aggregates by binding to proteins due to hydrophobic interaction
• Oxidised fatty acid and secondary products of autoxidation especially aldehydes are much more damaging to protein solubility as they are able to form covalent bonds with reactive protein groups.

TMAO —>TMA + formaldehyde (HCHO)

So aldehydes is very reactive compound bind to some groups in protein side chain and form intra and intermolecular methylene bridges. By removing water soluble substrates and enzyme system responsible for the degradation of TMAO the undesirable protein changes can effectively be reduced.