Chemical a long ?-helical coiled-coil tail and two

Chemical
composition of fish

                 The main constituents of fresh
fish are water (65-85 %), protein (15-24 %), fat (0.1-22 %), carbohydrate (1-3
%) and inorganic substances (0.8-2 %). The amount of fish meat varies according
to the species, age, part of body, pre or post-spawning season and the feeding
conditions (Suzuki, 1981). Protein is a major composition of fish muscle with
the range of 15-20 % (wet weight). Protein compositions of fish vary, depending
upon muscle type, feeding period, and spawning, etc. Hashimoto, et al. (1979) determined the protein
compositions of the dark and the white muscle from sardine (Sardinops melanosticta).

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2.2.
Muscle protein  

2.2.1 Myofibrillar
protein 

      Myofibrillar proteins are the major
proteins in fish muscle. Normally, these proteins account for 65-75 % of total
protein in muscle, compared with 52-56 % in mammals (Mackie, 1994). These
proteins can be extracted from the muscle tissue with neutral salt solutions of
ionic strength above 0.15, usually ranging from 0.30 to 0.70. The myofibrillar
proteins are related with the water hoding capacity and other func tional properties
of proteins such as gelation etc. (McCormick, 1994).  Myofibrillar proteins are highly reactive in their unfolded state.
A gel results when reactive protein surfaces form a 3 dimensional network entrapping water. Figure 17
illustrates the 3 dimensional protein network formed during gelation of surimi
(Morrissey et al., 1995). Contractile proteins, which
are different in size and location in the muscle, are listed in Table 1 (Ashie
and Simpson, 1997).

 

 

Myosin  

Myosin
is a large asymmetric molecule that has a long ?-helical coiled-coil tail and
two globular heads with an approximate weight of 500 kDa  (Hodge et al., 2000).  The basic body plan of myosin consists of an
N-terminal head or motor domain, a light chain-binding neck domain, and a class
conserved, C -terminal tail domain and has been categorized into over twenty
different classes  (Mooseker et al.,
2008) .  The head or motor domain has a
core sequence that is highly conserved in all myosin classes, and it contains
the ATPase active site (Holmes, 2008)Myosin is the major muscle protein that is
found in fish and comprises approximately 55-60% of the myofibrillar proteins
(Lanier et al., 2005) .  Skeletal myosin
can be broken up into six polypeptide chains, two heavy chains and four light chains.  Myosin light chains typically range from 17
to 25 kDa.  These amino acid chains are
non -covalently attached to the myosin head 
(Lanier et al., 2005) .  Myosin can
also be broken into fragments by proteolysis (Szent -Görgyi, 1953). 

Table1.
Contractile protein in food myosystems.

Protein

Relative abundance
(%)

Size (kDa)

Location

Myosin

50-60
 

470

Thick
filaments

Actin

15-30

43-48

Thin
filaments

Tropomyosin

5

65-70

Thin
filaments

Troponins

5

 

Thin
filaments

Troponin-C

 

17-18

 

Troponin-I

 

20-24

 

Troponin-T

 

37-40

 

C-
protein

140

Thick
filaments

?  – Actin

180-206

Z-disc

Z-nin

300-400

Z-disc

Connective
/ Titin

5

700-1000

Gap
filaments

Nebulin

5

~
600

N2-line

 

Actin

Actin,
which comprises of about 20% of the total myofibrillar protein, is the major
component of the thin filament of the myofibril (Suzuki, 1981). Actin exists in
two forms – globular, G-actin and fibrous, F-actin. G-actin is a monomer of 42
KD molecular weight proteins and polymerises to F-actin depending on the ionic
strength of the medium of extraction (Shenouda and Pigott, 1975; Stryer, 1995).
Fish actin in contrast to that from bovine sources, does not gel on heating in
the presence of sodium chloride, a property characteristic of myosin.It forms a
curd instead of a gel and thus, does not contribute to the elasticity of fish
gels (Sano et al., 1989a). Sano et. aI., (1989b) further stated that the
increase in elasticity of fish protein gel is proportional to the F-actin/myosin
ratio and F-actin adds the viscous element to the natural actomyosin
suspension.

Tropomyosin

Tropomyosin,
the third major component of structural proteins (Mannherz and Good, 1976),
plays a role in the regulation of calcium dependent interaction of actin and myosin.
In skeletal and cardiac muscles it forms an integral part of the thin filament
of sarcomere and involves in the calcium regulatory system for contraction and
relaxation. Situated in the two grooves of the double stranded structure of filamentous
actin, tropomyosin forms a long filament by aggregation of individual
molecules. Throughout its entire length it interacts with seven actin monomers
on each of the two strands of F-actin. It also binds one Mole of troponin
complex. As a result of the binding of Ca2+ to troponin C, tropomyosin may
alter its position in the groove of actin filament and permits interaction of myosin
heads and actin monorners (Mannherz and Good, 1976). Tropomyosin  does 
not  contribute to  the 
gel-forming  ability of fish  meat. Alaska Pollock  tropomyosin 
forms a  transparent  solution of low  viscosity 
in  NaCI  even 
at 9%  w/w (Sikorski.  1994a). ropomyosin  is an 
a-helical  protein  that forms a 
two-stranded  coiled-coil
(Huang  et al.,  2004). 
It  is  similar 
to  myosin  in 
amino acid  content  and it 
accounts  for  about 10 -12 
% of the  total  myofibrillar proteins.  In skeletal and cardiac  muscle, it 
forms an integral  part of
the  thin filament of sarcomere  and involved 
in  the  calciulll 
regulatory system  for  contraction 
and relaxation (Mannterz and Good. 1976).

Troponin

Troponin
(Suzuki, 1981) is a protein highly essential for the action of tropomyosin in
muscle contraction. The protein isolated from rabbit has a molecular weight of
about 80,000 and is formed of three subunits namely troponin-T which combines
with tropomyosin, troponin -1 which inhibits the action of ATPase and
troponin-C which combines with calcium. The troponin from fish sources is also
more or less similar,of course with species difference. Troponins isolated
from  the 
skeletal muscles of carp.  tilapia.  big 
eye tuna.  mackerel. and rainbow
trout  ‘were  able 
to  form  a 
functional  complex  with carp 
tropomyosin (Seki  and
Hasegawa.  1978).  Troponin 
C and troponin  I  from 
lobster  and crayfisll muscles
were found to exist  in several  isoforms 
(Nishita and Ojima. 1990).

Paramyosin

Paramyosin
(Sikorski, 1994) is characteristic of invertebrates (3% in scallop, 14% in
squid, 19% in oyster and 38% in smooth muscle of oyster) and is present in 0.1
to 10% of myosin. Theparamyosin is characterised by the presence of large concentrations
of amide, acidic amino acid residues like glutamic acid (20-23%), aspartic acid
(12%), and basic amino acid residues like arginine (12%), lysine (9%) and small
amounts of proline (Kantha, et al., 1990). The paramyosin rods form the thick
core of myofibrilsof invertebrate muscle, which is covered by a layer of myosin
and was reported to have a structural function affecting the orientation of the
myosin molecule. Functionally paramyosin affects the rheological properties of
gels prepared from invertebrate meat by adding elasticity and cohesiveness to
the gel than that prepared from fish gels. The action of paramyosin is due to
the inhibition of dissociation of myosin from actin (Sano et. al., 1989c).

 

 

 

Sarcoplasmic
protein

Scopes (1970) described Weber and Meyer’s (1933) experiments on
extraction of  sarcoplasmic proteins. He
noted that “the early work was carried out with water  extracts, which were then dialysed to very
low ionic strength, precipitating the so- called globulins, the albumin
remaining in solution.” Bate-Smith (1937) subdivided the albumin portion of the
sarcoplasmic proteins by electrophoresis into those that  were “slow migratory,” referred to a “myogens,”
and those that were “fast  migratory”,
referred to as “myoalbumins”. Baranowski (1939) crystallized a muscle  protein, that he called “myogen A.” Jacob
(1947) showed that the myogen  component
could be separated into several fractions by electrophoresis

 The sarcoplasmic proteins usually refer to the proteins of die sarcoplasm
as
well as die components of the extracellular fluid and the sarcoplasm. The sarcoplasmic
proteins comprise about 20-35% of the total muscle proteins and are commonly
called
myogens (Mackie, 1994: Pearsons and young,1989). Despite their diversity,
sarcoplasmic
proteins share many common physicochemical properties. Most are of relatively
low
molecular weight high isoelectric pH, and 
globular or rod-shaped structures. The
sarcoplasmic proteins are extracted by homogenizing the muscle tissue with
water or
solutions of neutral salts of ionic strength below 0.15. Among the sarcoplasmic
enzymes
influencing the quality of fish, the enzymes of die glycolytic pathway and the
hydrolytic
enzymes of die lysosomes are found to be important (Sikorski  et al.,1990a). The content of sarcoplasmic

protein
in fish meat varies with fish species, but is generally higher in pelagic fish
such as sardine and mackerel and lower in demersal fish (Suzuki, 1981).
Benjakul  et al. (2004a) reported that the sarcoplasmic
fraction from bigeye snapper muscle possessed cross-linking activity towards
myosin heavy chain (MHC).

 

Stroma
protein

Stroma  is  the 
protein,  which  forms 
connective  tissue, representing
approximately 3%  of total protein
content of fish muscle. It cannot be  extracted
by water, acid, or  alkali solution an d neutral
salt solution of 0.01-0.1 M concentration. The component of stroma is  collagen, elastin or both (Suzuki, 1981).  Elastin is very resistant to moist heat and
cooking, normally it is a reflection of the different structural arrangements
of muscles in fish, compared to mammals (Mackie,1994).

Suitable
species for surimi production

The technology of surimi processing was first commercialised
in 1960. By 1965 Alaska Pollock (Thengra calcogrammis) surimi was being produced
on factory ships (Suzuki, 1981). Surimi Processing According to him Atka mackeral
(Pleurogrammus azonus), horse mackeral (Trachus japonicus) and lizard fish
(Shurida undosquamis) were also used for production of surimi. Fish like cod,
hake, whiting, Atlantic menhaden, croaker, Chilean mackeral, New Zealand hoki
are found to be suitable for producing surimi (Young, 1978). Mac Donald et al.
(1990) demonstrated the use of stabilized mince produced from New Zealand hoki
(Mhcruronus novaezelandiae) as surimi source. Pacific whiting (flerluccius productus)
has been a good source of surimi production (Chang-Lee et al., 1990).

Many
researchers have investigated the use of fatty fish such as herring (Hastings
et al., 1990; Gill et al., 1992), mackeral (Shimizu, 1976; Katoh et al., 1989)
and sardines (Nonaka et al., 1989; Roussel and Cheftel, 1990; Saeki et al.,
1991) in production of surimi. Species such as Alaska pollock, croaker,jack
mackeral, threadfin bream, blue whiting, sardine, lizard fish, eel, barracuda
and leather jacket, have been recognised to give-good quality surimi (Lee,
1984, 1986; Yean, 1993). The gel-forming ability of dark muscle fish meat  has been known to be lower than that of  ordinary muscle (Chen, 2002; Ochiai et al., 2001).

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