353
Shark skin gelatin properties also differ from those of bony fi sh. Gelatin fi lm
from shark skin has a lower water vapour permeability (WVP) and higher opacity at
280 nm (UV wavelength) than have gelatin fi lms from other fi sh. This gelatin fi lm can
thus be applied to pharmaceutical products or foods rich in fat due to its excellent
barrier properties against water vapour and UV. However, WVP of shark skin gelatin
fi lm was higher than that of other edible fi lms (Limpisophon et al. 2009 , 2010 ).
How is possible to isolate gelatin from the rigid shark skin? Recently, Kharyeki
et al. ( 2011 ) proposed the following procedure. Frozen shark skin was thawed overnight at 4 °C, and then the residual meat on skin was removed manually. The skin
was cut into the 2–3 cm
2 pieces and then washed with cold tap water (8 °C). About
100 g of skin was used for each treatment. To remove non-collagenous proteins, the
prepared skin was treated with fi ve volumes (v/w) of cold NaOH (0.01–1 N) at
4 °C. The samples were then washed with tap water until neutral or faintly basic
pHs of wash water was obtained. The skins were then soaked in cold HCl (0.01–1 N)
at 4 °C with a ratio of 1:5 (w/v). The samples were washed out with cold tap water.
Each treatment was repeated three times, with a total time of 1 h. For water extraction, fi ve volumes (w/v) of distilled water was added into the sample and then heated
at 55 °C (±0.2) (3–8 h) in a water bath. After the extraction, gelatin solutions were
fi ltered using two layer fi lter cloth to remove the skin residues.
Changes in functional properties of shark ( Isurus oxyrinchus ) cartilage gelatin
produced by different drying methods have been reported by Kwak et al. ( 2009 ).
Freeze-dried gelatin was found to have the strongest gel strength, while gelatins
made at high temperatures formed weaker gels. The 135-kPa gel strength of freezedried gelatin was relatively high. While foam formation ability of the freeze-dried
gelatin was the highest, its foam stability was the lowest. In addition, spray-dried
gelatin had the best emulsion capacities. Dynamic viscoelastic properties of shark
cartilage gelatins prepared by these drying methods were closely correlated with
their gel strength. Elasticity modulus and loss modulus of the freeze-dried gelatin
had higher values than those prepared by hot-air drying and spray drying; viscoelastic properties of the freeze-dried gelatin were maintained longer than those of other
drying methods.
The method for extraction of gelatin from shark cartilage has been also proposed
(see, for example, Cho et al. 2004 ). Thus, cleaned shark cartilage was soaked in
eight volumes of (v/w) of sodium hydroxide solution (1–2 N) at 8 °C in a 200 rpm
shaking incubator for 2–4 days, to remove the non-collagen protein and subcutaneous tissue after they were swollen. The alkali treated shark cartilage was washed,
neutralized with 2 N HCl and rewashed. For hot-water extraction, seven volumes of
(v/w) of distilled water were added. Gelatin was extracted at the pre-determined
temperatures (40–80 °C) and times (1–5 h) in a water bath. The extracted solutions
(pH 8) were centrifuged for 30 min at 900 g at 30 °C. The upper phase was vacuumfi ltered with a fi lter paper, the fi ltered solution vacuum-concentrated to 10 brix at
60 °C, and fi nally dried for 24 h in a hot-air dryer.
Similar to other the fi sh gelatins discussed above, gelatins of shark origin can be
produced in different physical forms and can be used as biocomposites. Incorporation
of fatty acids (stearic and oleic) into edible fi lms based on blue shark ( Prionace
9.2 Shark Skin and Cartilage Gelatin
Shark skin gelatin properties also differ from those of bony fi sh. Gelatin fi lm
from shark skin has a lower water vapour permeability (WVP) and higher opacity at
280 nm (UV wavelength) than have gelatin fi lms from other fi sh. This gelatin fi lm can
thus be applied to pharmaceutical products or foods rich in fat due to its excellent
barrier properties against water vapour and UV. However, WVP of shark skin gelatin
fi lm was higher than that of other edible fi lms (Limpisophon et al. 2009 , 2010 ).
How is possible to isolate gelatin from the rigid shark skin? Recently, Kharyeki
et al. ( 2011 ) proposed the following procedure. Frozen shark skin was thawed overnight at 4 °C, and then the residual meat on skin was removed manually. The skin
was cut into the 2–3 cm
2 pieces and then washed with cold tap water (8 °C). About
100 g of skin was used for each treatment. To remove non-collagenous proteins, the
prepared skin was treated with fi ve volumes (v/w) of cold NaOH (0.01–1 N) at
4 °C. The samples were then washed with tap water until neutral or faintly basic
pHs of wash water was obtained. The skins were then soaked in cold HCl (0.01–1 N)
at 4 °C with a ratio of 1:5 (w/v). The samples were washed out with cold tap water.
Each treatment was repeated three times, with a total time of 1 h. For water extraction, fi ve volumes (w/v) of distilled water was added into the sample and then heated
at 55 °C (±0.2) (3–8 h) in a water bath. After the extraction, gelatin solutions were
fi ltered using two layer fi lter cloth to remove the skin residues.
Changes in functional properties of shark ( Isurus oxyrinchus ) cartilage gelatin
produced by different drying methods have been reported by Kwak et al. ( 2009 ).
Freeze-dried gelatin was found to have the strongest gel strength, while gelatins
made at high temperatures formed weaker gels. The 135-kPa gel strength of freezedried gelatin was relatively high. While foam formation ability of the freeze-dried
gelatin was the highest, its foam stability was the lowest. In addition, spray-dried
gelatin had the best emulsion capacities. Dynamic viscoelastic properties of shark
cartilage gelatins prepared by these drying methods were closely correlated with
their gel strength. Elasticity modulus and loss modulus of the freeze-dried gelatin
had higher values than those prepared by hot-air drying and spray drying; viscoelastic properties of the freeze-dried gelatin were maintained longer than those of other
drying methods.
The method for extraction of gelatin from shark cartilage has been also proposed
(see, for example, Cho et al. 2004 ). Thus, cleaned shark cartilage was soaked in
eight volumes of (v/w) of sodium hydroxide solution (1–2 N) at 8 °C in a 200 rpm
shaking incubator for 2–4 days, to remove the non-collagen protein and subcutaneous tissue after they were swollen. The alkali treated shark cartilage was washed,
neutralized with 2 N HCl and rewashed. For hot-water extraction, seven volumes of
(v/w) of distilled water were added. Gelatin was extracted at the pre-determined
temperatures (40–80 °C) and times (1–5 h) in a water bath. The extracted solutions
(pH 8) were centrifuged for 30 min at 900 g at 30 °C. The upper phase was vacuumfi ltered with a fi lter paper, the fi ltered solution vacuum-concentrated to 10 brix at
60 °C, and fi nally dried for 24 h in a hot-air dryer.
Similar to other the fi sh gelatins discussed above, gelatins of shark origin can be
produced in different physical forms and can be used as biocomposites. Incorporation
of fatty acids (stearic and oleic) into edible fi lms based on blue shark ( Prionace
9.2 Shark Skin and Cartilage Gelatin