323
similar proportions. A rather wider range of composition is observed in fi sh than in
mammals, which is not surprising in view of the greater evolutionary age of fi shes.
Hydroxyproline, in particular, is notably low, although showing considerable variation among fi sh species (Takahashi and Yokoyama 1954 ). Increased amounts of the
aliphatic hydroxyl amino acids serine and threonine were present in all the fi sh
proteins examined, compared with the amounts in mammalian collagen. The
hydroxylysine content was substantially increased in two of the fi sh materials. The
increase of hydroxyl groups in the molecule, owing to the larger numbers of aliphatic hydroxy amino acid residues in fi sh, was approximately equal to the loss of
groups from the diminished number of hydroxyproline residues. This balancing
effect results in the collagen molecule containing approximately the same proportion of hydroxyl groups in fi sh and mammals (Eastoe 1957 ).
Kawaguchi ( 1985 ) investigated the differences in the chemical composition
between shark dentine and skin with respect to their hydroxylation and phosphorylation. The author reported that “The hydroxylation of prolyl and lysyl
residues occurred more in the dentine alpha chains than in the skin chains.
Among the four alpha chains, the phosphate content was the highest in the alpha
2 chain of the dentine collagen. These differences in hydroxylation and phosphorylation have been observed among alpha chains in mammalian mineralized
and unmineralized tissues. The preferential dimerization to form alpha 1-alpha 2,
characteristic of shark-skin collagen, was not observed in the dentine collagen,”
(Kawaguchi 1985 ).
As recently reviewed in Hayashi et al. ( 2012 ), “glycine is the most abundant
amino acid [ in fi sh ] collagens and accounted for more than 30 % of all amino acids.
Further, the degree of hydroxylation of proline was calculated to be 40–48 %, which
was also similar level to that of the mammalian (about 45 %). The linear relationship between collagen stability and hydroxyproline content was demonstrated by
that the degree of hydroxylation of proline in the fi sh collagen peptides. This was
calculated to be about 35 %,” (Hayashi et al. 2012 ).
The physico-chemical properties of marine fi sh collagens as well as their molecular forms (Kimura and Ohno 1987 ), subunits (Kimura et al. 1987 ), and selfassembly (Nomura et al. 1997 ) have all been thoroughly investigated. The high
solubility of fi sh skin collagen upon heating has been known for a long time
(Gustavson 1942 ). In the comparative study by Rose et al. ( 1988 ), it was found that
the hydration of warm-water fi sh collagen is greater than that of cold-water fi sh collagen (halibut). Although the intrinsic viscosities of warm-water fi sh (bigeye-tuna,
carp and catfi sh) collagens are almost the same, the hydrated volume of bigeye-tuna
collagen is approximately 1.5 and 3 times those of freshwater fi shes, such as carp
and catfi sh collagens respectively. It was calculated that the denaturation temperatures of halibut, bigeye-tuna, carp and catfi sh collagens are 17, 31, 32 and 26–30 °C
respectively (Rose et al. 1988 ).
As an alternative for the mammalian collagens, nowadays, especially fi sh collagen has gained increasing interest. As recently reviewed by Simpson et al. ( 2012 ),
it can be generally isolated and manufactured from by-products generated during
processing of both freshwater and marine fi sh; including deep-sea species (Wang
et al. 2007b ). The potential raw materials include skin (Nagai et al. 2002 ), bone
8.1 Isolation and Properties of Fish Collagens
similar proportions. A rather wider range of composition is observed in fi sh than in
mammals, which is not surprising in view of the greater evolutionary age of fi shes.
Hydroxyproline, in particular, is notably low, although showing considerable variation among fi sh species (Takahashi and Yokoyama 1954 ). Increased amounts of the
aliphatic hydroxyl amino acids serine and threonine were present in all the fi sh
proteins examined, compared with the amounts in mammalian collagen. The
hydroxylysine content was substantially increased in two of the fi sh materials. The
increase of hydroxyl groups in the molecule, owing to the larger numbers of aliphatic hydroxy amino acid residues in fi sh, was approximately equal to the loss of
groups from the diminished number of hydroxyproline residues. This balancing
effect results in the collagen molecule containing approximately the same proportion of hydroxyl groups in fi sh and mammals (Eastoe 1957 ).
Kawaguchi ( 1985 ) investigated the differences in the chemical composition
between shark dentine and skin with respect to their hydroxylation and phosphorylation. The author reported that “The hydroxylation of prolyl and lysyl
residues occurred more in the dentine alpha chains than in the skin chains.
Among the four alpha chains, the phosphate content was the highest in the alpha
2 chain of the dentine collagen. These differences in hydroxylation and phosphorylation have been observed among alpha chains in mammalian mineralized
and unmineralized tissues. The preferential dimerization to form alpha 1-alpha 2,
characteristic of shark-skin collagen, was not observed in the dentine collagen,”
(Kawaguchi 1985 ).
As recently reviewed in Hayashi et al. ( 2012 ), “glycine is the most abundant
amino acid [ in fi sh ] collagens and accounted for more than 30 % of all amino acids.
Further, the degree of hydroxylation of proline was calculated to be 40–48 %, which
was also similar level to that of the mammalian (about 45 %). The linear relationship between collagen stability and hydroxyproline content was demonstrated by
that the degree of hydroxylation of proline in the fi sh collagen peptides. This was
calculated to be about 35 %,” (Hayashi et al. 2012 ).
The physico-chemical properties of marine fi sh collagens as well as their molecular forms (Kimura and Ohno 1987 ), subunits (Kimura et al. 1987 ), and selfassembly (Nomura et al. 1997 ) have all been thoroughly investigated. The high
solubility of fi sh skin collagen upon heating has been known for a long time
(Gustavson 1942 ). In the comparative study by Rose et al. ( 1988 ), it was found that
the hydration of warm-water fi sh collagen is greater than that of cold-water fi sh collagen (halibut). Although the intrinsic viscosities of warm-water fi sh (bigeye-tuna,
carp and catfi sh) collagens are almost the same, the hydrated volume of bigeye-tuna
collagen is approximately 1.5 and 3 times those of freshwater fi shes, such as carp
and catfi sh collagens respectively. It was calculated that the denaturation temperatures of halibut, bigeye-tuna, carp and catfi sh collagens are 17, 31, 32 and 26–30 °C
respectively (Rose et al. 1988 ).
As an alternative for the mammalian collagens, nowadays, especially fi sh collagen has gained increasing interest. As recently reviewed by Simpson et al. ( 2012 ),
it can be generally isolated and manufactured from by-products generated during
processing of both freshwater and marine fi sh; including deep-sea species (Wang
et al. 2007b ). The potential raw materials include skin (Nagai et al. 2002 ), bone
8.1 Isolation and Properties of Fish Collagens