Impact of zinc salts on heat-induced aggregation of natural actomyosin from yellow stripe trevally

Impact of zinc sulphate (ZnSO₄) and zinc chloride (ZnCl₂) on heat-induced aggregation of natural actomyosin (NAM) extracted from yellow stripe trevally (Selaroides leptolepis) was investigated. In the presence of ZnSO₄ or ZnCl₂, the transition temperature (T_max) of myosin shifted from 47.83 ± 0.30 °C to 46.05 ± 0.36 and 46.49 ± 0.49 °C, with the coincidental decreases in ΔH from 1.07 ± 0.03 J/g to 0.63 ± 0.02 and 0.67 ± 0.04 J/g, respectively (P < 0.05). Additionally, Ca²⁺–ATPase activity of NAM decreased with increasing the concentrations of ZnSO₄ or ZnCl₂ during heating up to 40 °C. During heating from 20 to 75 °C, higher turbidity, surface hydrophobicity and disulphide bond formation were obtained in NAM added with ZnSO₄ or ZnCl₂ at temperatures ranging from 40 to 75 °C, compared with the control. Nevertheless, a higher aggregation was found in NAM added with ZnSO_4, compared with ZnCl_2. Zeta potential (ζ) analysis suggested that the surface of NAM added with ZnSO₄ became less negatively charged, compared with that of ZnCl₂ counterpart. Transmission electron microscopy showed that the structure of NAM was highly interconnected, finer and denser when zinc salts, especially ZnSO₄ were incorporated. Therefore, ZnSO₄ could be used to induce aggregation of fish muscle proteins, thereby improving gelling property of fish mince or surimi.