Roles of Amino Acid Properties in Regulating the Gel Characteristics of Low-Salt Pacific White Shrimp (Litopenaeus vannamei) Surimi

To improve the gel quality of low-salt shrimp surimi gel (SSG) from Pacific white shrimp (<i>Litopenaeus vannamei</i>), L-arginine (L-Arg), L-lysine (L-Lys), and L-proline (L-Pro) were used as partial substitutes for NaCl. The effect of the three amino acids on gel properties, protein conformation, microstructure, and in vitro digestion of low-salt SSG were systematically analyzed. Macro-/microstructural analyses revealed that L-Arg, L-Lys, and L-Pro promoted denser three-dimensional networks in low-salt SSG with smaller pore sizes. Compared with the low-salt control (LC) group, the addition of L-Arg, L-Lys, and L-Pro significantly increased the gel strength of low-salt SSG. Cooking loss was significantly decreased from 10.80% (LC group) to 1.89-4.31%. Protein solubility and turbidity results demonstrated that all amino acids markedly enhanced protein solubilization and inhibited protein aggregation. L-Arg and L-Lys mainly promoted hydrogen and disulfide bonds, but reduced hydrophobic interactions and ionic bonds. L-Arg impaired digestibility only in the gastric phase, whereas L-Lys suppressed digestibility across both gastric and intestinal phases. Through molecular docking technology, ASN-238 and LYS-187 of myosin (the dominant gel-forming protein) are the key shared binding residues with three amino acids. These findings suggest that amino acids provide a feasible approach to specifically modulate the gel characteristics of low-salt surimi products.