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20 Fish Collagen 383FACTOR AFFECTING COLLAGEN
PROPERTIESSome factors have been known to influence the collagen prop-
erties. pH and salt concentration were reported to affect water-
binding capacity, viscosity, and emulsifying properties of col-
lagen from fish muscle and skin connective tissues (Montero
et al. 1991). Jongjareonrak et al. (2005) reported that maximum
solubility in 0.5 M acetic acid of collagen from brownstripe red
snapper (Lutjanus vitta) was observed at pH 3 and 4 for ASC and
PSC, respectively. A sharp decrease in solubility was observed in
the presence of NaCl above 2% and 3% (w/v) for ASC and PSC,
respectively. Collagens from the skin and bone of bigeye snapper
(P. tayenus) had the highest solubility at pH 2 and 5, respectively.
No changes in solubility were observed in the presence of NaCl
up to 3% (w/v). However, a sharp decrease in solubility was
found with NaCl above 3% (w/v) (Kittiphattanabawon et al.
2005). Where pH was between 2 and 4, the solubility and water
binding capacity of trout (Salmo irideusGibb) collagen were
highest, but in the addition of NaCl, functionality was reduced
(Montero et al. 1991). Montero et al. (1999) also reported that
solubility, apparent viscosity, and water-binding capacity of col-
lagenous material from hake and trout showed the maximum
values at pH levels between 2 and 4 and at concentrations less
than 0.25 M NaCl. Furthermore, emulsifying capacity decreased
as the NaCl concentration increased and was highest at pH levels
between 1 and 3 (Montero et al. 1991).
Collagen properties are also affected by processing parameters
such as freezing, heating, and so on. Montero et al. (1995) com-
pared four stabilizing methods: (1) freezing, (2) freeze-drying,
(3) partial solubilization with 0.05 M acetic acid then freezing,
and (4) partial solubilization with 0.05 M acetic acid then freeze-
drying on the functional properties of collagen from plaice skin.
Only freeze-drying caused reduction in solubility and emulsify-
ing capacity. Viscosity was greatest when samples were presol-
ubilized. Emulsifying capacity was not changed when samples
were frozen and decreased when they were either freeze-dried or
presolubilized. Optimum water-holding capacity was observed
in samples, which were previously solubilized. During the stor-
age of fish on ice, a progressive change in solubility of muscle
collagen was found. For insoluble collagen, significantly lower
values were detected at day 15 compared with day 0. A little
increase in ASC was found, while no changes were seen in PSC
during storage (Eckhoff et al. 1998). Therefore, some cleavage
of intermolecular cross-links seems to occur during storage on
ice (Eckhoff et al. 1998).APPLICATIONS OF COLLAGEN
Food ApplicationsThe collagen protein can be refined so that it can be used in pro-
cessed meat products to improve protein functionality through
the immobilization of free water, increasing the stability of the
finished product (Prabhu et al. 2004). Kenney et al. (1992) used
pork collagen as an inexpensive adjunct to increase cooking
yields and tensile strength in restructured beef. In addition,the use of 10% raw and preheated pork collagen reduced (P
<0.05) product initial cohesiveness and juiciness and tended
(P<0.09) to reduce beefiness. Utilization of pork collagen in
boneless cured pork that incorporates pale, soft, and exudative
(PSE) meat increases water-holding capacity and has the poten-
tial to improve protein functionality characteristics of the prod-
uct (Schilling et al. 2003). Effects of pork collagen in emulsified
and whole muscle products have also been evaluated. Prabhu
et al. (2004) found that incorporation of pork collagen at 1%
and above significantly (P<0.05) increased cooked and chilled
yields in frankfurters but did not have any effect in hams. Purge
was significantly (P<0.05) reduced in both frankfurters and
hams after 4 weeks of storage. Sensory difference testing showed
no significant difference up to 2% usage level of pork collagen in
both frankfurters and hams (P>0.05). The use of pork collagen
as a binder and extender in emulsion sausages and hams pro-
vides for the absorption and binding of moisture, so that during
thermal processing, cook losses are minimized. (Prabhu et al.
2004). Effects of raw material and the inclusion of chicken colla-
gen on the protein functionality of chunked and formed chicken
breast manufactured from 100% PSE like and 100% normal
broiler breast with either 0% or 1.5% collagen were determined
(Schilling et al. 2005). Inclusion of collagen was effective in
decreasing cooking loss and increasing protein–protein bind.
PSE like with no collagen had lower (P<0.05) protein–protein
bind than normal meat with collagen. Schilling et al. (2004) also
found that inclusion of turkey collagen improved the texture of
turkey breast deli products through increasing the protein’s abil-
ity to bind with each other in pale meat and was effective in
decreasing cooking and purge loss in both pale and normal sam-
ples. These results revealed that addition of collagens is effective
in increasing water-holding capacity and has the potential to im-
prove quality characteristics of products made from either pale
or normal raw material.Biomedical ApplicationsThe primary reason for the usefulness of collagen in biomedical
application is that collagen can form fibers with extra strength
and stability through its self-aggregation and cross-linking (Lee
et al. 2001). Out of the ten collagen types that have been charac-
terized, types I, III, and V are the most desirable for biomedical
applications because of their high biocompatibility and low im-
munogenicity (Antiszko et al. 1996). Uses of collagen as surgical
suture, hemostatic agents, and tissue engineering including basic
matrices for cell systems and replacement/substitutes for artifi-
cial blood vessels and valves were reported (Lee et al. 2001).
As a commercial medical product, collagen can be part of nat-
ural, stabilized tissue that is used in the device, for example,
as in a bioprosthetic heart valve, or it can be fabricated as a
reconstituted, purified product from animal sources, for exam-
ple, as in wound dressings (Ramshaw et al. 2009). Polymers
of natural origin that function as regeneration templates have
so far been synthesized as graft copolymers of collagen and
chondroitin 6-sulfate, a glycosaminoglycan. Certain collagen-
graft glycosaminoglycans can induce synthesis of dermis within
a wound bed in guinea pigs in which the epidermis and the