TGase activity of surimi paste before setting increased from 7.6
to 17.6 unit/ml extract as the concentration of NFB increased from
0 to 2 g/100 g, respectively (Fig. 2). With increasing MFB, TGase
activity increased slightly (from 7.6 to 9.5 unit/ml extract). It was
postulated that calcium ion activates endogenous TGase by
inducing a conformational change to the enzyme, which exposes
the TGase active site to a substrate (Nozawa, Cho, & Seki, 2001). The
data indicated that calcium ion from Pacific whiting fish bone was
released to activate endogenous TGase. It was consistent with the
result reported by Hemung (2013) that endogenous TGase extracted
from tilapia filletwas activated by calcium from tilapia fish bone
powder. Calcium compounds from fish bone are hard to dissolve;
nevertheless, Kim, Yeum, and Joo (1998) reported more soluble
calcium (105.0 mg/100 g) was contained in mackerel surimi gels
made with 0.9 g/100 g Alaska pollock fish bone powder than the
control surimi gel (2.9 mg/100 g). Increased TGase activity for surimi
mixed with NFB confirmed that NFB had a higher concentration
of free calcium ions than MFB.
TGase activities of the pastes with