The Atlantic cod (Gadus morhua) fishery generates substantial primary products for human consumption, but processing operations yield an abundance of by-products (skins, frames, viscera, backbones, etc.). These by-products may represent 30–70% of the fish’s wet weight, depending on filleting and handling processes. Valorization — converting this biomass into food ingredients — aligns with circular economy principles, reduces waste disposal costs, and can generate high-value nutritional products. Recent research has focused on extraction, functionalization, and characterization of cod by-products for food applications, which we herein review.
This review synthesizes the latest scientific studies on technologies and applications for Atlantic cod by-products use in food ingredients, emphasizing protein recovery, functional components, and nutritional quality.
Protein Recovery from Cod By-Products
Subsection: Fish Protein Isolates via pH-Shift Technology
Isoelectric solubilization/precipitation (ISP), also known as the pH-shift method, is one of the most extensively studied techniques for extracting muscle proteins from seafood by-products. In this process, proteins are solubilized at extreme pH (acidic or alkaline) and precipitated at their isoelectric point to recover fish protein isolate (FPI).
High-Molecular-Weight vs. Low-Molecular-Weight Isolates
A recent study applied ISP to Atlantic cod by-products to produce FPI with distinct molecular characteristics:
- FPI-1 (high molecular weight) formed at lower alkaline solubilization temperatures, showing higher α-helix content, strong gelling behavior, and high denaturation temperatures (163°C).
- FPI-2 (low molecular weight) formed at higher temperatures and exhibited weaker gel networks.
These isolates demonstrated excellent gelling and nutritional properties — critical attributes for food ingredient applications in products such as enriched gels, surimi analogs, and high-protein formulations.
Functional Implications
The recovered isolates integrate essential amino acids and gelation properties comparable to traditional protein sources. Their rheological and textural attributes make them suitable for incorporation in structured food products (e.g., gels, sausages, or emulsified items).
Subsection: Protein Hydrolysates and Bioactive Components
Beyond whole protein isolates, protein hydrolysates — peptides produced by enzymatic or hydrothermal cleavage — are studied for functional and bioactive food applications.
Subcritical Water Extraction (SBW) and Hydrolysis
The SBW process treats cod frames under high pressure and elevated temperatures (e.g., 90–250°C) to extract soluble proteins, peptides, and amino acids:
- Up to ~57.7 g extract per 100 g frames with nearly complete protein recovery.
- Extracts predominantly contain collagen and collagen fragments, important for gelling and textural cues.
- The lowest temperature fraction (90°C) showed potential anti-inflammatory activity in cell models, indicating possible nutritional and nutraceutical benefits.
- Residual hydroxyapatite (bone mineral) suggests potential biomedical or nutraceutical valorization beyond food ingredients.
Enzymatic Hydrolysates
Several studies have used proteolytic enzymes to generate hydrolysates from cod backbones or skins with:
- High degrees of hydrolysis (indicative of peptide liberation).
- Demonstrated antioxidative, antimicrobial, or functional emulsifying properties.
Such hydrolysates serve as bioactive food ingredients, potentially enhancing food quality and offering health-linked benefits when used in fortified foods.
Collagen and Structural Protein Components
Subsection: Marine Collagen Extraction
Fish skins and connective tissues are rich sources of Type I collagen, which provides structural integrity and functional utility in food systems (e.g., gelatin, hydrocolloids). Research has shown:
- Marine collagen extracted from cod skin is structurally analogous to mammalian collagen and may serve as a gelation agent, stabilizer, or texturizer.
- Collagen yields from cod skins can be optimized using acid extraction or alternative technologies like CO₂-acidified water methods.
- Marine collagen from by-products offers potentially superior safety profiles (e.g., reduced zoonosis risk) relative to terrestrial collagen sources.
Collagen fractions can form gels, foams, or structured matrices desirable in confectionery, meat analogs, or encapsulation systems.
Subsection: Functional and Nutritional Characterization
Hydrolyzed collagen — wherein collagen protein is broken down into smaller peptides — has functional advantages such as:
- Enhanced solubility and digestibility.
- Potential biological activity (e.g., antioxidative properties).
- Use as texturizers, emulsifiers, or health-focused supplements in functional foods.
These properties position collagen hydrolysates from cod by-products as promising food ingredients with dual structural and nutritive roles.
Oils and Lipid-Associated Ingredients
Subsection: Marine Oil Recovery
Viscera and liver fractions contain lipid-rich materials. Research on thermal oil extraction from cod residuals has shown:
- Oils are rich in omega-3 fatty acids — important for cardiovascular and cognitive health.
- Storage and handling conditions significantly influence oil quality, oxidation levels, and yields.
- Optimizing raw material freshness can increase yields and quality.
These recovered lipids may be refined into food-grade oils or used to fortify functional foods with essential fatty acids.
Subsection: Implications for Food Formulation
Recovered oils from by-products expand ingredient portfolios for enriched formulations, including:
- Nutrition-fortified foods (high omega-3 content).
- Emulsions and spreads with tailored lipid profiles.
- Specialty nutraceutical products.
Challenges and Regulatory Considerations
Though scientific studies demonstrate the technical feasibility of various valorization strategies, industrial adoption requires:
- Safety and regulatory approval for human food use of by-product derived ingredients in each jurisdiction.
- Scalable, cost-effective processing systems with controlled quality standards.
- Consumer acceptance of ingredients sourced from processing streams despite comparable safety and nutritional value.
Further research on digestibility, allergenicity, and sensory impacts of ingredients derived from cod by-products remains limited and required for regulatory compliance.
Conclusion
Recent research shows that Atlantic cod by-products use can be transformed into high-value food ingredients through advanced processing technologies. Key findings include:
- Fish protein isolates with superior functional properties via pH-shift methods.
- Protein hydrolysates and peptides with potential biofunctional benefits.
- Marine collagen and hydrolyzed structural proteins suitable for texture and health-oriented foods.
- Omega-3-rich lipids derived from residual viscera and liver fractions.
Collectively, these valorization pathways contribute to circular economy goals, enhance the sustainability of seafood processing, and expand the portfolio of functional ingredients for food innovation. However, broader industry adoption depends on scalable technologies, regulatory frameworks, and continued research to validate safety and efficacy in specific food applications.
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