In the fish industry up to 70% of the entire fish ends up as side-streams. In order to reduce the amount of side-streams and meet the demand of the growing population, a higher utilization degree of the fish is needed. The aim of this study was to use cod backbone for enzymatic production of bioactive hydrolysates with antioxidative and antimicrobial properties. Three different enzymes were applied (Alcalase, Neutrase and Protamex) and hydrolysis was carried out for ½ - 6h within the enzyme’s optima for pH and temperature. Alcalase treated samples had the highest protein extracted yield (PEY) followed by Protamex treated samples and lowest PEY was obtained with Neutrase. No correlation was observed between PEY and degree of hydrolysis (DH). All hydrolysates had antioxidant activities measured by radical scavenging and iron chelation in vitro assays. For radical scavenging activity, Protamex treated hydrolysate showed lowest IC50 and had a molecular weight < 10 kDa. Whereas for iron chelation activity, the control samples (no enzyme added, but heat treated) showed similar or lower IC50 with molecular weights of 200 – 10 kDa. Amino acid composition measured on selected hydrolysates suggested that not only composition of amino acid, also but sequence and size influence the properties. None of the hydrolysates showed antimicrobial activity measured by the Minimum Inhibitory and disk diffusion assays. In summary, the results showed that protein with antioxidant activity can be extracted from the cod backbone and make it possible to use the side-streams generated in the fish industry.

Preventing metal-catalyzed lipid oxidation in food products, which decreases nutritional value and sensory quality, is crucial in the food industry. This is typically achieved through the use of metal-chelating molecules. While the ferrozine assay is widely used to screen protein hydrolysates for metal chelating activity, it has proven difficult to use with pure peptides. This study evaluates the potential of Surface Plasmon Resonance (SPR) and Electrically Switchable Nanolever Technology (switchSENSE®) as alternative screening methods. Unfortunately, solubility issues and large standard deviations precluded a direct correlation between the ferrozine assay and these biosensor techniques. Both techniques, however, were able to quantitatively distinguish between two peptides with very similar sequences despite the absence of a correlation between dissociation constants determined by SPR and switchSENSE®. This study highlights the potential of SPR and switchSENSE® for screening the metal chelating activity of pure peptides, advancing the understanding of peptide-metal ion interactions.

Enriching foods with long-chain (LC) n-3 polyunsaturated fatty acids (PUFAs) requires a delivery emulsion system, which is both thermodynamically and oxidatively stable. The antioxidant and stabilizing properties of three types of polysaccharide extracts from brown algae Saccharina latissima with mixed composition of polysaccharides (SA: 98% Sodium alginate, SF: 90% alginate and 9% fucoidan, SL: 14.5% fucoidan, 9.5% laminarin and co-extracted non-polysaccharides) were evaluated. SA, SF, SL and REF (added commercial sodium alginate) all showed in vitro ferrous ion chelating ability in the order: SA(99%)>SL(78%)>REF(31%)>SF(16%). The difference in antioxidant activity between SA, REF and SF appeared related to structural differences of alginate (M/G ratio). A storage trial was conducted using 70% (w/w) fish oil-in-water delivery emulsions added sodium caseinate (NaCas) (0.23 wt%) as emulsifier in combination with SA, SF, SL or commercial NaAlg (REF) in different concentrations (C1=0.1, C2=0.2 C3=0.3 and C4=0.4 wt%). A control with only NaCas were included (CON). The physical (e.g. creaming and droplet-size distribution) and oxidative (peroxide value and volatiles) stability of the emulsions, were evaluated (12 days, dark at 20˚C). Acceptable physical stability (creaming index, CI) was found for, REF (all concentrations), SF=0.2 wt% (C2), SL and SA=0.3 wt% (C3) and 0.4 wt% (C4). In general, the oxidative stability decreased by adding REF, SA and SF (except for REF at C1), as prooxidant activity was observed. However, SA showed antioxidant activity against formation of 2-ethylfuran. SL showed antioxidant activity in decreasing formation of volatile compounds in emulsions when added in concentrations above 0.2 wt%.