The Combined Effect of Transglutaminase and Protease Inhibitors on the Thermal Gelation of Actomyosin Sol from Carp and Salmon Muscles

Abstract

In order to improve the poor gel-formability of underutilized fish species for surimi-based products, such as carp and salmon, we attempted to induce setting effect to actomyosin gel with microbial transglutaminase (MTGase) and to inhibit the gel weakening (modori) caused by non-proteolytic and proteolytic processes. Carp and salmon actomyosin sots (90mg protein/g in 0.5M NaCl-5mM CaCl₂ at pH 7.0) without MTGase exhibited similar changes in storage modulus (G') with a temporal sharp reduction (non-proteolytic modori) at 53 and 48°C for carp and salmon, respectively, though the G' magnitude of salmon sol was twice that of carp during heating from 5 to 80°C. Compared to walleye pollack surimi gel, however, both gels were extremely weak at the end of heating.
The addition of MTGase to actomyosin sol could induce setting effect and resulted in elastic and rigid gels with a great increase in G' magnitude as well as gel breaking strength. Salmon myosin heavy chain was more easily and extensively polymerized than that of carp. Gel weakening was slightly improved by the addition of protease inhibitors, E64 and aprotinin. The effects of protease inhibitors on carp actomyosin gelation were more distinctive when combined with MTGase. For salmon actomyosin gel, the protease inhibitor had less effective due to lower remaining of endogenous proteases in the actomyosin sol. Upon the setting at 40°C, the addition of 5 unit/g MTGase substantially increased in G' and extensively reduced the non-proteolytic modori. Under identical gelling conditions, salmon actomyosin sol was capable of forming more rigid and elastic gel than that of carp.