Value added fish by-products - Nordic Innovation

It is well known that the source of raw material, the degree of cross-linking and the method of
manufacture, which depends on temperature, time and pH, affect the molecular weight
distribution as well as the mechanical properties of the resulting gelatin.
The molecular weight of a single α-chain has been reported to be 95-100 kg/mol, but during
the pre-treatment and the extraction of gelatin, peptide bonds in the primary structure are
ruptured providing subunits of the α-chains. Covalent cross-links between the α-chains can
survive the manufacturing treatments, providing fractions of β-chains (two covalently cross-
linked α-chains), γ-chains (three covalently cross-linked α-chains) and components with even
higher molecular weights (Veis 1964; Piez 1968; Finch & Jobling 1977; Hinterwaldner 1977;
Ledward 1986; Norland 1990).
The mammalian gelatins with good gel forming properties are produced during the initial
extractions made at low temperature while the subsequent extractions made at successively
higher temperatures provide gelatins exhibiting reduced mechanical properties due to
increasing hydrolysis (Finch & Jobling 1977; Hinterwaldner 1977; Ledward 1986; Schrieber
& Gareis 2007).
The procedures used for preparing fish gelatins typically involve acid or alkaline pre-
treatment of the fish skins prior to gelatin extraction. Although a number of different pre-
treatment conditions have been reported the initial extraction temperatures for mammalian
gelatins (between 45 and 60°C) have been adopted for the extraction of cold water fish
gelatins (Guðmundsson & Hafsteinsson 1997; Zhou & Regenstein 2005; Arnesen & Gildberg
2007). From optical rotation measurements the denaturation temperature of cold water fish
collagen was estimated to be between 15 and 20°C (Joly-Duhamel et al. 2002). This indicates
that the temperature adopted for the extraction of cold water fish gelatin (45°C or above) is
unnecessarily high.
2.5.1 Utilization of fish gelatin
The commercial interest in cold water fish gelatin has been relatively low due to its
suboptimal physical properties. This is also reflected by the worldwide annual production of
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