Salting-in effect on muscle protein extracted from giant squid (Dosidicus gigas)

• Paramyosin was separated from giant squid (Dosidicus gigas) myofibrillar protein.
• The separated paramyosin was purified.
• CD analysis showed paramyosin molecule conformation changed with KCl concentration.
• Conformation changes were reversible.
• Conformation changes caused salting-in effect.

The salting-in effect on muscle protein is well-known in food science but hard to explain using conventional theories. Myofibrillar protein extracted from the giant squid (Dosidicus gigas) was selected as a model muscle protein to study this mechanism in KCl solutions. Changes in the secondary structures of myofibrillar protein molecules caused by concentrated salts, particularly in the paramyosin molecule conformation, have been reported. Zeta-potential determinations showed that these secondary structures have modified protein molecule surfaces. The zeta-potential of the myofibrillar protein molecules fell from −7.24 ± 0.82 to −9.99 ± 1.65 mV with increasing salt concentration from 0.1 to 0.5 M. The corresponding second virial coefficient increased from −85.43 ± 3.8 × 10−7 to −3.45 ± 1.3 × 10−7 mol mL g−2. The extended law of corresponding states suggests that reduced attractive interactions increase the protein solubility. Solubility measurements in alternating KCl concentrations showed that the conformational change was reversible.