- Existing research reports the importance of brine injection technology in enhancing the quality of muscle products such as poultry, beef, and pork. In fish, the utilization of brine injection technology is well-known for delivering marinade ingredients for salted or smoked fish production. Until now, there has been limited published scientific evidence on the incorporation of brine ingredients containing protease inhibitors to improve the quality of fresh or frozen fish fillets. Thus, the studies presented in this thesis focused on improving the quality of Pacific whiting (Merluccius productus) fillets through brine injection technology. Pacific whiting fillets are not considered desirable in the U.S. market because their meat is easily softened during slow cooking.
The first study explored whether multi-needle injection technology is applicable to the improvement of Pacific whiting raw fillet quality. Color, texture, rancidity, moisture and protein were determined to understand how brine treatments
affected appearance, oxidative stability and composition of the fillets. The impact of brine ingredients on myofibril protein was evaluated by gel electrophoresis. All brines were formulated with a base solution (3% sodium tripolyphosphate and 3% salt). Treatments consisted of base brine (B), base brine + 3% egg white (B[subscript EW]), and base brine + 0.1% xanthan gum+ 3% dried potato extract (B[subscript PE]). Ten fillets were injected per treatment and a 10% brine uptake was targeted for all fillets. Actual brine incorporation was 12.35 ± 2.28%. The lightness (L*) value of raw fillets indicated that B[subscript EW] and B[subscript PE] were darker than C and B (P < 0.05). Breaking strength demonstrated higher variability in non-injected samples than in injected samples. Enzyme assays showed no differences between all treatments when it was tested using buffer at pH 5.5 (P = 0.06). SDS-PAGE analysis showed minor changes in myofibril proteins between injected fillets and non-injected fillets.
The second study aimed to evaluate the brine effectiveness in inhibiting protease activity in the fillet through heating. Control samples included non-injected (NI) fillets and fillets injected with water (W) only. For all other treatments, brines contained 3% (w/w) salt and sodium tripolyphosphate as a base brine (B). Additional, brine treatments with egg white were a combination of the base brine (B) with either 1, 2 or 3% egg white (B[subscript 1EW], B[subscript 2EW], B[subscript 3EW]). For potato extract, 0.1% xanthan gum was added to the base brine to aid in its suspension (BXG). Potato extract was added to B[subscript XG] at similar levels as egg white (B[subscript 1PE], B[subscript 2PE], B[subscript 3PE]). Previously frozen butterfly fillets were tempered to 2.0 ± 1.0 °C, injected with a selected treatment, vacuum packaged and immediately cooked in either one of two different heating conditions. Vacuum packed fillets were either submerged in water at 90 °C for 20 min to achieve a final internal temperature 62.8 °C (145 °F) or submerged in a 60 °C water bath for 30 min and then immediately transferred to a 90 °C water bath for 20 minutes. The pH, moisture, crude protein, total extractable protein, total non-extractable protein, texture profile analysis, and SDS-PAGE electrophoretic pattern in cooked fillets were determined. For TPA measurements, an uninjected cod sample was used as a reference sample. Compositional analysis determined the cooked NI fillet was less moist than all injected samples (P < 0.05), suggesting TPA attributes would be higher than injected samples, which was confirmed. Protein patterns from SDS-PAGE electrophoresis indicated that the myosin bands were slightly diminished when fillets were heated at 60 °C prior to cooking at 90 °C for all treatments, except in fillets containing egg white or potato extract ingredients, suggesting these treatments provided some protection to myofibrillar structure. Fillets cooked using the challenge heat treatment were significantly (P < 0.05) softer than those cooked using the sous vide for all TPA attributes.
Additionally, future research considerations that would benefit the applicability of the injection process to fillet quality improvement should include determining the appropriate fish size to target for the injection process, the shelf life of injected fillets during frozen or refrigerated storage, and consumer acceptance of the injected fillets.