Value added fish by-products - Nordic Innovation

Kristinsson & Rasco 2000a). In addition, except for the deficit of a few amino acids,
hydrolysates have a high nutritional value (Shahidi et al. 1995; Slizyte et al. 2005b).
Several studies have indicated that peptides derived from fish proteins have antioxidative
properties in different oxidative systems (Jeon et al. 2000; Jung et al. 2003; Rajapakse et al.
2005; Kristinsson 2006; Klompong et al. 2007; Klompong et al. 2008; Samaranayaka & Li-
Chan 2008; Yang et al. 2008). The antioxidant activity of proteins and peptides can be the
result of specific scavenging of radicals formed during peroxidation, scavenging of oxygen
containing compounds, or metal-chelating ability (Gutierrez et al. 2003; Kristinsson 2006).
Metal catalysed decomposition of lipid peroxides is one of the dominant oxidative pathways
that occur in food (Mcclements & Decker 2000). Because of this, proteins can inhibit lipid
oxidation by sterically hindering the interaction of metals and dispersed lipids, reducing its
ability to decompose lipid peroxides. Many proteins whose specific biological function is not
to store or transport metals are still capable of chelating metals. The ability of a protein to
chelate metals is dependent on pH. A net anionic charge will be established on a protein at pH
above the pI. That leads to electrostatic attraction between the protein and cationic metal in
continuous phase, which inhibits lipid oxidation reactions (Elias et al. 2008).
The ability of proteins to scavenge radical has been shown in several studies (Thiansilakul et
al. 2007; Slizyte et al. 2009). However, this is not conclusive evidence that they are
antioxidants. To be an effective antioxidant, proteins must be more oxidatively stabile than
unsaturated fatty acids and the resulting protein radical must not promote lipid oxidation
(Elias et al. 2008). Proteins are also capable of altering the development of rancidity in
unsaturated fats and oils by adducting volatile aldehydes (Elias et al. 2008). This pathway is
not truly an antioxidant mechanism, but it will inhibit rancidity by transforming lipid
oxidation products into non-volatile compounds.
Production of fish protein hydrolysates with antioxidant properties will enable production of
protein enriched and oxidatively stable seafood. While hydrolyzed proteins have good
antioxidant activity, it is still not well-understood how the composition of peptides influences
the ability to inhibit lipid oxidation.
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