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392 Part 3: Meat, Poultry and Seafoods(low pH) or for the maximum physical properties (neutral pH)
(Johnston-Banks 1990). Basically, more efficient pretreatment
conditions allow the manufacturer to use lower extraction tem-
peratures, and still obtain gelatins with high bloom strength
(Johnston-Banks 1990). Shorter time is generally associated
with higher extraction temperatures if neutral pH levels are cho-
sen. However, lower gel strength is obtained (Johnston-Banks
1990). Muyonga et al. (2004) reported that Nile perch skin ex-
tracted at higher temperature yielded lower gel strength, melt-
ing point, setting temperature, and longer setting time. Yang
et al. (2007) also reported that gelatin from channel catfish skin
showed lower gel strength as extraction temperature was in-
creased from 60◦Cto75◦C. Additionally, gelatin extracted from
the skin of brownbanded bamboo shark and blacktip shark us-
ing higher temperature had decreasing band intensity of major
components (α-,β-andγ-chains) as well as increasing low-
molecular weight components. Such changes correlated well
with lowered bloom strength. Shorter chain fragments of gelatin
could not form the junction zone, in which the strong network
could be developed (Kittiphattanabawon et al. 2010) (Fig. 21.2).DryingAfter extraction, the gelatins are filtered to remove suspended or
insoluble matters including fat, unextracted collagen fibers, and
other residues. Diatomaceous earth or activated carbon can be
used to make gelatin solution clear. The final stage is evapora-
tion, sterilization, and drying. These are performed as quickly as
possible to minimize loss of properties (Johnston-Banks 1990).
Kwak et al. (2009) extracted gelatin from shark cartilage using
three drying methods, (1) freeze drying, (2) hot-air drying, and
(3) spray drying. Freeze-dried gelatin showed the highest gel
strength and foam formation ability, but its foam stability was
the lowest. Nevertheless, spray-dried gelatin exhibited the best
emulsion capacities.FISH GELATIN
Fish gelatin from both cold- and warm-water fish has been ex-
tracted under different conditions (Table 21.2) (Montero and
Gomez-Guill ́ en 2000, Jamilah and Harvinder 2002, Cho et al. ́
2004, Muyonga et al. 2004, Zhou and Regenstein 2004, Cho
et al. 2005, Jongjareonrak et al. 2006a, Arnesen and Gildberg
2007, Cheow et al. 2007, Yang et al. 2007, Nalinanon et al. 2008,
Aewsiri et al. 2008, Gimenez et al. 2009, Aewsiri et al. 2009a, ́
Jongjareonrak et al. 2010, Kittiphattanabawon et al. 2010). How-
ever, gelatins from these sources have limited application as they
have lower gel strength and their gels are less stable, compared
with those from their mammalian counterparts. The differences
between fish and mammalian gelatin mainly depend on their
molecular weight distribution and amino acid content, espe-
cially the content of imino acid (proline and hydroxyproline)
(Johnston-Banks 1990). However, gelatin from skin of brown-
banded bamboo shark extracted under the appropriate conditions
had properties similar to those of mammalian gelatin. The gel
could be set at room temperature and had the bloom strength
comparable to commercial bovine gelatin (Kittiphattanabawonet al. 2010). This shark skin gelatin might contain similar amino
acids, especially imino acids, as well as could form gel compa-
rable to that from mammalian source.FUNCTIONAL PROPERTIES OF GELATIN
Gelatin is a gelling protein, which has widely been applied in
the food and pharmaceutical industries (Cho et al. 2005). Gelatin
gel has "melt-in-the-mouth" characteristic and shows an excel-
lent release of flavor (Choi and Regenstein 2000). Moreover, its
functional properties, including gelation, emulsifying proper-
ties, foam-forming properties, and film formation, are important
for the food industry as it enhances the elasticity, consistency,
and stability of food products, and it is also used as an outer
film to protect foods against light and oxygen (Montero and
Gomez-Guill ́ en 2000). ́GelationAn aqueous solution of gelatin becomes slightly viscous at tem-
perature above its melting temperature. On cooling, the gelatin
solution starts to form transparent elastic thermoreversible
gels when the temperature is below the setting temperature
(Normand et al. 2000, Babin and Dickinson 2001). The interac-
tion initiates a disorder-to-order transition, as the random coil
gelatin molecules seek to return to the ordered triple helix con-
formation. Gelatin gel is a reversibly cross-linked biopolymer
network stabilized mainly by hydrogen-bonded junction zones
(Fig. 21.2). Furthermore, hydrophobic and ionic interactions are
also involved in the gelation of gelatin (Fig. 21.2). The gelation
of gelatin is dependent on many factors such as source of raw
material for gelatin extraction, presence of endogenous protease
in raw material, and the conditions for gelatin extraction, partic-
ularly temperature, play a role in gelation of resulting gelatin.
High temperature generally renders high yield, the gelatin so
obtained has shorter chains (Kittiphattanabawon et al. 2010).
These fragments cannot form the junction zone effectively. As a
result, a poor gel is formed or gel of these fragments cannot set,
especially at room temperature (25◦C) (Fig. 21.2).Source of Raw MaterialThe sources of raw materials influence the composition of
gelatin, especially amino acid composition of gelatin, which
affect gelling properties. Generally, the imino acid content of
gelatin obtained from mammals is higher than that of gelatin
from both warm-water and cold-water fish (Table 21.3). Imino
acid content correlates with gel strength of gelatin. Imino acid,
especially hydroxyproline, is involved in gel formation by act-
ing as a H-donor, in which hydrogen bond can be formed with
an adjacent chain possessing H-acceptor (Fig. 21.2). The hy-
droxyl group of the hydroxyproline plays a part in the stability
of the helix by interchain hydrogen bonding via a bridging water
molecule as well as direct hydrogen bonding to a carbonyl group
(Wong 1989).
Fish gelatin has been recognized to exhibit poorer gelling
properties than its mammalian counterpart. Gelatin from