Effect of pH on the gelation of walleye pollack surimi and carp actomyosinpastes

The effect of pH on thermal gelation and transglutaminase (TGase; EC2.3.2.1 3)induced suwari (setting) of surimi and actomyosin pastes was investigated . A strong and elastic gel was produced from walleye pollack surimi paste a t pH 7.0 in the presence of Ca2+ using a two-step heating method. In contra st, walleye pollack actomyosin paste formed a weak gel under the same condi tions as a result of the low concentration of endogenous TGase. In the pres ence of EGTA [ethyleneglycol bis(2-aminoethylether) tetraacetic acid], weak gels were formed at pH values of 7.0 and 6.0. Non-proteolytic modori (gel weakening) occurred extensively in the course of actomyosin gelation, but n ot in surimi gelation. Maximum TGase-induced myosin heavy chain cross-linki ng was observed at a slightly higher pH of 7.5 than at the optimal pH of en dogenous TGase activity; the difference being derived from different substr ates. Gelation of carp actomyosin paste at pH values of 5.5, 6.0, 6.5 and 7 .0 was monitored by measuring storage modulus (G ') and loss modulus (G "). A weak gel was formed at all pH values, but a slightly rigid and less elas tic gel was obtained at lower pH values. The addition of microbial TGase (M TGase) formed strong elastic gels at pH 7.0 and 6.5. MTGase cross-linked my osin heavy chains even at pH 5.5, but contributed neither to suwari respons e nor strong gel formation. Overall, results suggest that the optimal pH fo r the gelation of surimi paste from easy-setting fish species is a compromi se between the pH-optima of TGase activity and of preferable actomyosin con formation for myosin cross-linking.