Acid-induced aggregation of actomyosin from silver carp (Hypophthalmichthys molitrix)

Acid-induced denaturation and aggregation properties of silver carp actomyosin added with d-gluconic acid-δ-lactone (GDL) during incubation at chilled temperature (4 °C) were studied. Actomyosin underwent aggregation with decreasing pH, as evidenced by increased turbidity and decreased protein solubility in 0.6 M NaCl solution. Ca²⁺-ATPase activity decreased continually with increasing incubation time in the presence of GDL, accompanied by an initial increase in surface reactive sulphydryl (SH) content, indicating the conformation changes of actomyosin during acidification. Protein solubility in selected solvents and electrophoresis analysis showed that the major myofibrillar proteins, particularly, myosin heavy chain and actin were involved in the formation of protein aggregates mainly through noncovalent bonds including hydrophobic interactions and hydrogen bonds during acidification. The slight decrease in total SH content during acidification suggested that disulphide bonds were also involved in acid-induced aggregation of silver carp actomyosin to a lesser extent.