Serine protease inhibitors from squid ovary: extraction and its effect on proteolysis and gel properties of surimi.

Serine protease inhibitors from squid ovary (SOSPI) were extracted using different extraction media and conditions. Optimal condition included 0.45 M NaCl for 1 h. After heat treatment at 70 °C for 10 min, the highest specific activity was obtained. Based on Sephadex G-75 gel filtration and activity staining, the major SOSPIs were present as monomer with molecular weight of 9.10 and 10.27 kDa. Impact of SOSPI on autolysis of bigeye snapper surimi was studied. Myosin heavy chain was more retained with coincidentally lower trichloroacetic acid-soluble peptide content as the level of SOSPI increased. When SOSPI at various levels (0.5-3%) was added into surimi, the highest breaking force of both kamaboko and modori gels containing 1% SOSPI was obtained. However, SOSPI had no effect on deformation of kamaboko gel but slightly increased the deformation of modori gel. SOSPI increased water holding capacity of both kamaboko and modori gels in a dose dependent manner, as indicated by the lowered expressible moisture content. SOSPI had no effect on the whiteness of both gels. Thus SOSPI can be used as the protein additive in surimi for increasing breaking force.