Thermal stability of fish natural actomyosin affects reactivity to cross-linking by microbial and fish transglutaminases.

Natural actomyosin (NAM) from Pacific whiting (PW) showed thermal transition temperatures by circular dichroism at 31.8 and 43.1°C, which were lower than those of threadfin bream (TB) NAM, 35.0 and 49.3°C. Endothermic transitions of PW-NAM by differential scanning calorimetry were at 31.8, 42.1 and 75.3°C, compared to 36.1, 50.9 and 78.4°C for TB-NAM. Based on surface hydrophobicity, α-helical content, and solubility, PW-NAM unfolded to a greater extent than did TB-NAM when incubated at 25°C for 4h and 40°C for 2h, suggesting its lower thermal stability. Transglutaminase generally catalyzed more extensive cross-linking of PW-myosin heavy chain (MHC) than TB-MHC, and the MHC cross-linking mediated by microbial transglutaminase (MTG) was greater than by fish transglutaminase (FTG). Textural properties of PW-NAM gels increased approximately 3.6-6.1-fold and 1.3-1.5-fold in the presence of MTG and FTG, respectively.