Injection of Natural Protease Inhibitors and Evaluation of Their Impact on Cooked Pacific Whiting (Merluccius productus) Fillets.

Brine injection of natural proteases, dried egg white (EW), and dried potato extract (PE), was investigated as a means to prevent softening during cooking of Pacific whiting fillets. Treatments included fillets injected with Water (W), 3% sodium chloride and 3% sodium tripolyphosphate brine (B), B with 0.1% xanthan gum (BXG ), B with 1%, 2%, or 3% EW (B1-3EW ), B with 1%, 2%, or 3% PE (B1-3PE ) or non-injected (NI). Non-injected Pacific cod (Cod) was also utilized as a reference for texture analysis. Fillets were subsequently cooked using cooking protocol 1 (90 °C for 20 min) or cooking protocol 2 (60 °C for 30 min then 90 °C for 20 min). Cooked fillet pH, moisture, total protein, total extractable protein (TEP), total non-extractable protein (TNEP), texture profile analysis (TPA), and electrophoretic pattern (SDS-PAGE) were measured. Cooking protocol 2 significantly reduced moisture, increased total protein, TEP and TNEP. Loss of moisture suggested cooking protocol 2 promoted proteolysis. Electrophoretic evaluations of the fillets treated with the cooking protocol 2 confirmed proteolysis was enhanced by cooking protocol 2 and myosin band integrity was protected in fillets containing natural protease inhibitors. For TPA, there was no significant difference between protease inhibitor types although means for BEW did trend higher than BPE . However, PCA analysis clearly demonstrated B2EW and B3EW fillets were most similar to Cod. Results demonstrated brine injection with protease inhibitors prevented fillet softening during cooking.

PRACTICAL APPLICATION: Texture softening in fish has typically been addressed by diverting product to lower-value minced applications where ingredients can be blended-in to counteract softening caused by enzymes. Investigations demonstrate feasibility of brine injection of protease inhibitor ingredient, dried egg white, to preserve protein integrity during cooking. Dried potato extract required a suspension aide, xanthan gum, in order to become sufficiently suspended in the brine for injection. Dried potato extract was able to inhibit protease activity, however, the suspension aide negatively impacted protein-protein interactions during cooking. An alternative suspension aide is therefore required for dried potato extract.