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382 Part 3: Meat, Poultry and Seafoodsin PSC by the albacore tuna pepsin did not significantly alter
surface charge of collagen (Nalinanon et al. 2010). However,
slight differences inζ-potential profiles of ASC and PSC from
shark skins were observed when porcine pepsin was used as
extraction aid. The difference in pI and the rate of changes in
ζ-potential between ASC and PSC from shark skins might be
caused by the different amino acids mediated by partial removal
of telopeptides by pepsin used (Kittiphattanabawon et al. 2010a,
2010c). It was noticed that PSCs from different sources showed
different pIs. Benjakul et al. (2010) reported that PSC of the
skin ofP. tayenusshowed a higher pI than those from the skin
ofP. macracanthus. For the same skin, PSCs prepared using
porcine pepsin possessed a lower pI than those prepared using
tongol tuna pepsin. Owing to the similar amino acid composi-
tion of all PSCs, the differences in net surface charge at differ-
ent pHs were most likely governed by the different unfolding
or exposure of charged amino acids, in which protonation or
deprotonation could take place to different degrees (Benjakul
et al. 2010). Thus, the different pepsins may cleave the telopep-
tide region at different sites, leading to differences in the ease of
conformational changes at different pHs and to different charges
at the surface (Benjakul et al. 2010, Kittiphattanabawon et al.
2010b). The pI of ASC and PSC of arabesque greenling was
estimated to be 6.31 and 6.38, respectively. Both collagens had
pI in a slight acidic pH. This might be due to higher content of
acidic amino acids, aspartic acid, and glutamic acid compared
with basic amino acids, including histidine, lysine, and arginine
(Nalinanon et al. 2010). The pI of collagens from the skin of
brownbanded bamboo shark and blacktip shark was reported in
the range of 6.21–7.02 (Kittiphattanabawon et al. 2010a, 2010c).
The pI of ASC and PSC from the cartilage of brownbanded bam-
boo shark and blacktip shark were estimated to be 6.53, 7.03,
6.96, and 7.26, respectively. The difference in pI between both
shark cartilages might be caused by the variation in their amino
acid compositions (Kittiphattanabawon et al. 2010b). Proteins
arise from different genes may have a variable number of amino
acids with charged side chains, resulting in different surface
charge and a variety of pI values (Bonner 2007).Invertebrate CollagenCollagens with different types and contents have been found in
invertebrates. The presence of homotrimetic collagen molecules
(α1) 3 has been demonstrated in the muscle of abaloneHalio-
tis discusand top shellTurbo cornutus(Yoshinaka and Mizuta
1999). Kimura and Matsuura (1974) reported that collagen ex-
tracted by limited digestion with pepsin from foot muscle of
abalone consisted ofα3 -chain, while collagens from the skins
of octopus and squid, and the subcuticular membranes of swim-
ming crab and spiny lobster had (α1) 2 α2, commonly found in
various vertebrate collagens. The squid and lobster collagens
contained the greater amount of glycosylated hydroxylysines
(mainly glucosylgalactosylhydroxylysine) than most vertebrate
collagens (Kimura and Matsuura 1974). On the other hand, bi-
valves have been shown to possess (α1) 2 α2 heterotrimers, which
have similar compositional features to vertebrate type I col-
lagen. The byssus threads of sea mussel (Mytilus edulis)andthe adductor muscles of pearl oyster (Pinctada fucata) con-
tained heterotrimer collagen (α1) 2 α2 (Yoshinaka and Mizuta
1999). Xuan Ri et al. (2007) reported that PSC from scallop
(Patinopecten yessoensis) mantle consisted of two different col-
lagen molecules, with different profiles in molecules, amino
acids, and peptide maps, and had different uronic acid contents
and gel-forming abilities.
Collagen in the mantle muscle of common squidTodaro-
des pacificusconsisted of two genetically distinct types of PSC
(Yoshinaka and Mizuta 1999). The major collagen, named type
SQ-I collagen, is insoluble in 0.5 M acetic acid containing
0.45 M NaCl, and has a similar amino acid composition to those
of vertebrate type I collagen. Type SQ-I collagen is the major
collagen in the cranial cartilage and skin of common squidT.
pacificusand in the skin and arm muscle of octopusOctopus vul-
garis. In addition, similar collagens have been isolated from the
sucker of cuttlefish and octopus. The minor collagen, called type
SQ-II, is very soluble in 0.5 M acetic acid containing 0.45 M
NaCl. Type SQ-II collagen has some compositional characteris-
tics similar to vertebrate type V collagen, showing a low level of
alanine and high level of hydroxylysine. Both type SQ-I and SQ-
II collagens are heterotrimers, of which the subunit compositions
are represented as [α1(SQ-I] 2 α2(SQ-I) and [α1(SQ-II] 2 α2(SQ-
II), respectively (Yoshinaka and Mizuta 1999). OctopusCallis-
toctopus arakawaiarm consisted of ASC and PSC at levels of
10.4% and 62.9%, respectively. PSC had a chain composition of
α 1 α 2 α3 heterotrimer, while ASC showed only a singleα-chain,
α1. The denaturation temperature of those collagens was lower
than that of porcine collagen (Nagai et al. 2002b). Nagai and
Suzuki (2002) found that the collagen extracted from the outer
skin of the paper nautilus was hardly solubilized in 0.5 M acetic
acid. The insoluble matter was easily digested by 10% pepsin
(w/v), and a large amount of collagen (PSC) was obtained with
about a 50% yield. PSC had a chain composition ofα 1 α 2 α 3
heterotrimer similar toC. arakawaiarm collagen. PSC from skin
of cuttlefish (S. lycidas) had a chain composition of (α1) 2 α2 het-
erotrimer, which was similar to Japanese common squid PSC.
The denaturation temperature of this collagen was 27◦C, that is
about 10◦C lower than that of porcine collagen.
The primary structure of PSC from rhizostomous jellyfish was
very similar to that of PSC from edible jellyfish mesogloea, but
it was different from those of the collagen from edible jelly-
fish exumbrella and the ASC from its mesogloea. The rhizosto-
mous jellyfish mesogloea collagen had a denaturation temper-
ature (Td) of 28.8◦C. This collagen contained a large amount
of a fourth subunit, designated asα4. This collagen may have
the chain composition of anα 1 α 2 α 3 α4 heterotetramer. Mizuta
et al. (1998) reported that collagen from muscle of Antarctic
krill,Euphausa superba, referred to asα1(Kr) component, con-
stituted more than 80% of the total pepsin-soluble collagen and
showed typical compositional feature of crustacean major col-
lagens, with low alanine and high hydroxylysine contents. The
α1(Kr) component was mainly distributed in relatively thick
connective tissues, epimysium and perimysium.α1(Kr) compo-
nent may functionally correspond to the majorα-component of
collagen in decapods,α1(AR-I) (AR-I : Arthropod-type I), and
comprise a major homotrimeric collagen molecule, [α1(AR-I) 3 ].