Influence of Ammonium Salt on the Formation of Pressure-induced Gel from Walleye Pollack Surimi

To investigate the effect of ammonium ion on the quality of pressure-induced gel, walleye pollack surimi was ground with NaCl, or NaCl containing a small amount of (NH4)2 SO4 or NH4Cl. The salt-ground meat was then treated under 300 MPa at 0°C for 10 min followed by storage at 5°C for 120 hours, and breaking strength and breaking strain together with subunit composition of myofibrillar protein were evaluated. Transglutaminase activities and ε-(γ-glutamyl) lysine contents were also measured. The results obtained were as follows: (1) Transglutaminase activity of the salt-ground meat was mostly inactivated by the pressure-treatment, (2) The rates of formation of cross-linked myosin heavy chain (60% of total protein) and of ε-(γ-glutamyl) lysine (2.7mg/g) in the pressure-induced gel were virtually identical with those in the setting gel from the same surimi, (3) The breaking strength of the pressure-induced gel reached more than twice that of the setting gel, (4) Addition of ammonium salts to the salt-ground meat largely suppressed the formation of cross-linked myosin heavy chain and of ε-(γ-glutamyl) lysine, while the breaking strength of the pressure-induced gel remained at half the level of that of the gel formed without ammonium salts. These results suggested that intermolecular hydrophobic interaction between myofibrillar proteins, which was formed through the pressure-treatment, might contribute to the production of an elastic gel.