Food Biochemistry and Food Processing

(Ben Green) #1
18 Proteomics in Fish Processing 409

1989), wheat flour baking quality factors (Dough-
erty et al. 1990), and soybean protein bodies (Lei
and Reeck 1987). In recent years, proteomic investi-
gations on fish and seafood products, as well as in
fish physiology, have gained considerable momen-
tum, as can be seen in recent reviews (Parrington
and Coward 2002, Piñeiro et al. 2003). Herein, re-
cent and future developments in fish and seafood
proteomics as relates to issues of concern in fish
processing or other quality considerations are dis-
cussed, paying particular attention to the as yet little
exploited potential for investigating the antemortem
proteome for the benefit of postmortem quality invo-
lution.


TRACKINGQUALITYCHANGESUSING
PROTEOMICS


A persistent problem in the seafood industry is post-
mortem degradation of fish muscle during chilled
storage, which has deleterious effects on the fish
flesh texture, yielding a tenderized muscle. This
phenomenon is thought to be primarily due to autol-
ysis of muscle proteins, but the details of this protein
degradation are still somewhat in the dark. However,
degradation of myofibrillar proteins by calpains and
cathepsins (Ladrat et al. 2000, Ogata et al. 1998) and
degradation of the extracellular matrix by the matrix
metalloproteases and matrix serine proteases, which
are capable of degrading collagens, proteoglycans,
and other matrix components (Lødemel and Olsen
2003, Woessner 1991), are thought to be among the
main culprits. Whatever the mechanism, it is clear
that these quality changes are species dependent
(Papa et al. 1996, Verrez-Bagnis et al. 1999) and,
furthermore, appear to display seasonal variations
(Ingólfsdóttir et al. 1998, Ladrat et al. 2000). For
example, whereas desmin is degraded postmortem
in sardine and turbot, no desmin degradation was
observed in sea bass and brown trout (Verrez-Bagnis
et al. 1999). Of further concern is the fact that sever-
al commercially important fish muscle processing
techniques, such as curing, fermentation, and pro-
duction of surimi and conserves, occur under condi-
tions conducive to endogenous proteolysis (Pérez-
Borla et al. 2002). As with postmortem protein
degradation during storage, autolysis during pro-
cessing seems to be somewhat specific. Indeed, the
myosin heavy chain of the Atlantic cod (Gadus
morhua) was shown to be significantly degraded


during processing of “salt fish” (bachalhau),where-
as actin was less affected (Thorarinsdottir et al.
2002). Problems of this kind, where differences are
expected to occur in the number, molecular mass,
and pH of the proteins present in a tissue, are well
suited to investigation using 2DE-based proteomics.
It is also worth noting that protein isoforms other
than proteolytic ones, whether they be encoded in
structural genes or brought about by posttranslation-
al modification, usually have a different molecular
weight or pH and can, therefore, be distinguished on
2DE gels. Thus, specific isoforms of myofibrillar
proteins, many of which are correlated with specific
textural properties in seafood products, can be
observed using 2DE or other proteomic methods
(Martinez et al. 1990, Piñeiro et al. 2003).
Several 2DE studies have been performed on
postmortem changes in seafood flesh (Kjærsgård
and Jessen 2003, Martinez and Jakobsen Friis 2004,
Martinez et al. 2001a, Martinez et al. 1990, Mor-
zel et al. 2000, Verrez-Bagnis et al. 1999) and have
demonstrated the importance and complexity of pro-
teolysis in seafood during storage and processing.
For example, Martinez et al. (1992) used a 2DE
approach to demonstrate different protein composi-
tions of surimi made from prerigor versus postrigor
cod, and they found that 2DE could distinguish be-
tween the two. Kjærsgård and Jessen, who used
2DE to study changes in the abundance of several
muscle proteins during storage of the Atlantic cod
(Gadus morhua),proposed a general model for post-
mortem protein degradation in fish flesh in which
initially calpains are activated due to the increase in
calcium levels in the muscle tissue. Later, as pH
decreases and ATP is depleted, with the consequent
onset of rigor mortis, cathepsins and the proteasome
are activated sequentially (Kjærsgård and Jessen
2003).

ANTEMORTEMEFFECTS ONQUALITY AND
PROCESSABILITY

Malcolm Love started his 1980 review paper on bio-
logical factors affecting fish processing (Love 1980)
with a lament for the easy life of poultry processors
who, he said, had the good fortune to work on a
product reared from hatching under strictly con-
trolled environmental and dietary conditions “so that
plastic bundles of almost identical foodstuff for man
can be lined up on the shelf of a shop.” Since the
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