12.5 Extraction of Collagen
267
Collagen content varies from species to species and also varies in different parts of
the animal. It also varies for different studies. Extraction yields of collagen from the
skin of C. catla and C. mrigala are 13 and 11.2%, respectively, while that from the
scales were 9.5 and 8.3, respectively, and 13 and 13.1%, respectively, from the fins
(Mahboob 2015). In jellyfish R. esculentum recent studies report a yield of 4.31%
(weight of dry collagen to weight of wet jellyfish) compared to other studies which
reported lower yields (Felician et al. 2019). A yield of 13.6% (dry collagen per wet
weight of skin) was obtained from acid extraction of collagen from Spanish mackerel
fish skin (Chi et al. 2014) while a 30% yield (dry weight of hydrolyzed collagen per
dry weight of fish scales) was obtained from hydrothermal extraction of hydrolyzed
collagen from fish scales of croaker fish (Olatunji and Denloye 2017). In another
study (Ahmed et al. 2019), a yield of 16.7% was reported for enzyme extraction of
collagen from skin of bigeye tuna using pepsin enzyme. Using acid extraction, the
acid-soluble collagen yield from the skin was 13.5% while yield of pepsin soluble
collagen from the scale and bones were 4.6 and 2.6%, respectively. The acid-soluble
collagen obtained from scales and bones of the tuna fish was negligible.
12.5.1 Extraction of Collagen from Combined Fish Waste
Collagen has been extracted from fish skins, scales and bones of a variety of fish
such as bigeye snapper, red snapper, carp, black drum, Nile perch and yellowfin tuna
(Ahmed et al. 2019; Olatunji and Denloye 2017; Mahboob 2015; Chi et al. 2014). Fish
skins can be sourced from fish processing factories where skinless fish fillets or other
fish products are made. Processing the skin separately from the bones and other parts
since the composition of bones and skin significantly varies. Separate extraction of
the different parts of the fish waste allows for better process optimization by tailoring
the operating conditions to the respective composition. However for practicality and
reduction of labor and process complexity, it is desirable to combine all the fish
wastes and extract collagen from the mixtures in one batch.
To extract collagen from combined fish waste both the chemical and enzymatic
method follows the same steps for pretreatment of the fish waste parts. Here, an
example method (Mahboob 2015) which was used as a general method to extract
collagen from scales, fin and fish skin is presented. Although the parts were separated, the same process conditions were applied to all parts. The different parts were
separated prior to extraction in order to analyze them separately for collagen contents
and structure in the different parts of the fish. The pretreatment stage is targeted at
removing non-collagenous proteins so that these are not extracted alongside the collagen and contaminate the extract. To achieve this, the mass is treated with an alkali,
most commonly sodium hydroxide at 0.1 M using a 10 ml solution per gram of fish
waste mass. This is carried out at a temperature of 4 °C under constant stirring for
6 h with the alkali solution changed every 2 h after which the spent alkali solution
must have been saturated with non-collagenous proteins that have been removed.
This is then washed with water until all the alkali with the non-collagenous proteins
267
Collagen content varies from species to species and also varies in different parts of
the animal. It also varies for different studies. Extraction yields of collagen from the
skin of C. catla and C. mrigala are 13 and 11.2%, respectively, while that from the
scales were 9.5 and 8.3, respectively, and 13 and 13.1%, respectively, from the fins
(Mahboob 2015). In jellyfish R. esculentum recent studies report a yield of 4.31%
(weight of dry collagen to weight of wet jellyfish) compared to other studies which
reported lower yields (Felician et al. 2019). A yield of 13.6% (dry collagen per wet
weight of skin) was obtained from acid extraction of collagen from Spanish mackerel
fish skin (Chi et al. 2014) while a 30% yield (dry weight of hydrolyzed collagen per
dry weight of fish scales) was obtained from hydrothermal extraction of hydrolyzed
collagen from fish scales of croaker fish (Olatunji and Denloye 2017). In another
study (Ahmed et al. 2019), a yield of 16.7% was reported for enzyme extraction of
collagen from skin of bigeye tuna using pepsin enzyme. Using acid extraction, the
acid-soluble collagen yield from the skin was 13.5% while yield of pepsin soluble
collagen from the scale and bones were 4.6 and 2.6%, respectively. The acid-soluble
collagen obtained from scales and bones of the tuna fish was negligible.
12.5.1 Extraction of Collagen from Combined Fish Waste
Collagen has been extracted from fish skins, scales and bones of a variety of fish
such as bigeye snapper, red snapper, carp, black drum, Nile perch and yellowfin tuna
(Ahmed et al. 2019; Olatunji and Denloye 2017; Mahboob 2015; Chi et al. 2014). Fish
skins can be sourced from fish processing factories where skinless fish fillets or other
fish products are made. Processing the skin separately from the bones and other parts
since the composition of bones and skin significantly varies. Separate extraction of
the different parts of the fish waste allows for better process optimization by tailoring
the operating conditions to the respective composition. However for practicality and
reduction of labor and process complexity, it is desirable to combine all the fish
wastes and extract collagen from the mixtures in one batch.
To extract collagen from combined fish waste both the chemical and enzymatic
method follows the same steps for pretreatment of the fish waste parts. Here, an
example method (Mahboob 2015) which was used as a general method to extract
collagen from scales, fin and fish skin is presented. Although the parts were separated, the same process conditions were applied to all parts. The different parts were
separated prior to extraction in order to analyze them separately for collagen contents
and structure in the different parts of the fish. The pretreatment stage is targeted at
removing non-collagenous proteins so that these are not extracted alongside the collagen and contaminate the extract. To achieve this, the mass is treated with an alkali,
most commonly sodium hydroxide at 0.1 M using a 10 ml solution per gram of fish
waste mass. This is carried out at a temperature of 4 °C under constant stirring for
6 h with the alkali solution changed every 2 h after which the spent alkali solution
must have been saturated with non-collagenous proteins that have been removed.
This is then washed with water until all the alkali with the non-collagenous proteins