Abstract: In order to develop a new fish species for producing surimi products, surimi from Clarias gariepinus was obtained by chopping the fish meat with added cryoprotectant after cooling it in an ice bath instead of the traditional process involving rinsing and dehydration. The effects of transglutaminase (TGase) combined with different concentrations of CaCl2 on the gel properties of unwashed surimi were examined by measuring texture characteristics, gel strength, water-holding capacity, protein covalent crosslinking, microstructure and dynamic rheology characteristics. The results showed that adding TGase could effectively enhance the gel properties of surimi. When the concentration of TGase was 0.4%, the gel properties of surimi were significantly changed with increasing Ca2+ concentration from 20 to 80 mmol/kg. Ca2+ at low concentration of 20 mmol/kg could activate TGase when they coexisted, enhancing gel strength (3 261.97 g·mm), elasticity (0.92), cohesiveness (0.81), resilience (0.47) and water retention (76.32%). In addition, it shortened the relaxation time T22, increased the elastic modulus G’, and made the microstructure more compact with less cavities. However, high Ca2+ concentration (40–80 mmol/kg) decreased the gel strength and elasticity, increased hardness and T22, and decreased water-holding capacity and the degree of protein covalent crosslinking. Therefore, adding 0.4% TGase and 20 mmol/kg CaCl2 could effectively improve the gel properties of surimi.

Key words: Clarias gariepinus; surimi; transglutaminase; calcium ion; gel properties