Seafood is highly susceptible to spoilage and deterioration. The high levels of polyunsaturated lipids in fish lead to lipid oxidation thus to rancidity in fish muscle, which is a major cause of quality deterioration in fish. The microbial activity in seafood products also causes production of off-flavors, off color, texture changes and results in heavy economic losses. Unlike most preservation techniques like freezing or refrigeration, CO can stabilize the heme proteins of fish muscle by maintaining these in their reduced state, leading to less lipid oxidation, and retaining the color of the fish muscle. CO binds to the heme group with great affinity replacing O₂ from the heme.

The objectives of this research were to quantify the effects of CO in Atlantic salmon (Salmo Salar), and the use of protein injection (salmon hydrolysates) as cryoprotectants. An enzymatic hydrolysis process was used to extract functional proteins from salmon frames using Protamex (a bacterial protease.) Since tons of fish and fish byproducts are wasted every year, these byproducts can be converted into useful functional proteins and injected to fish muscle as cryoprotectants. Predominantly phosphates, whey and soy protein, sucrose sorbitol mixture, and salts are being used to improve the water holding capacity thus texture of muscle foods. One objective was to study the effect of hydrolysates, prepared by enzymatic hydrolysis of salmon frames, on the water holding capacity, texture and lipid oxidation, by injecting the protein hydrolysate solution to increase the weight of the fish muscle by up to 10%.

Atlantic salmon (Salmo salar) from Chile was received from a certified distributor in Miami Fl. not more than 3 days after harvest. The fish were filleted and divided in 3 groups: a control, CO treated, and CO treated and injected with hydrolysates. Each group had 3 replicates.

Fresh salmon (fillets) were be placed in a box built with Lexan sheets (polycarbonate material) and flushed with 100% CO. The gas was flushed seven times the volume of the box to assure the desired concentration. The box was sealed with a door that had a gasket to avoid any leakage. Before CO treatment, fish proteins (hydrolysates) were injected into the fish muscle as cryoprotectants to stabilize proteins against denaturation and their effects were evaluated after the freezing-thawing cycle. All samples were vacuum packed and frozen for 30 days at -30ºC. All the analyses were done in triplicate. Lipid oxidation was measured by (TBARS), CO levels in the fish by GC (FID) and spectrophotometer, Color by Machine Vision and L, a* and b* values were recorded, texture by Instron TPA profile, water holding capacity by a Sorvall RC-5B Refrigerated Superspeed Centrifuge, freshness by E-nose, and microbial count by Total Plate Count (TPC). Results were analyzed statistically using analysis of variance to look for significant differences between the 3 treatments at each storage day

CO did significantly (P>0.05) change the color (a* value) of Atlantic salmon fillets at day 5 after treatment but remained about the same during frozen storage. The study showed that there was nearly no effect of CO on the growth of microorganisms. Before treatment, all samples had less than 100 cfu/g. At day 39 after thawing, the control had 10³ cfu/g, and the treated 10⁴ cfu/g.

TBARS values confirmed the effectiveness of CO reducing lipid oxidation. These values were significantly less (P< 0.05) for the CO and CO+ injected treated salmon compared to the controls during most part of frozen storage. CO uptake was significantly higher at day 2 after treatment between samples. Water holding capacity was significantly improved by using cryoprotectants at 10% injection level. Texture values for hardness were significantly less (P< 0.05) at day 2 for samples, CO treated and injected. E-nose results indicated no difference in odor between the treatments.