Fish propose the time before stiffness will be

Fish bleeding is a way that can postpone the rigor
onset (Huss, 1995), with this propose the time before
stiffness will be prolongedfoloowed by a better fillet quality. (Ando, Nishiyabu, Tsukamasa, &
Makinodan, 1999) confirmed that, more than half the volume
of blood in muscle is drained by bleeding which can remove the available nutrients
are needed for autolytic changes. Furthermore, in unstressed fish the amount of
Ca2+ is low and bleeding remove some parts of this Ca2+
as well. In this case, the amount of Ca2+ which is needed to onset
the rigor is reduced and this would be another reason that can delay the rigor
onset.

Immediat bleeding would keep the
freshness of muscle for a longer time and maintenance the fillet firmness
during the storage time. It has been demonstrated that inadequately bled or non-bled
fish show the lower overall quality in the fish fillet as bleeding decrease the
total haemoglobin in the muscle. For example, (Richards
& Hultin, 2002) showed higher amount of total haem
in un-bled fish compared to the bled fish.  

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Beside the effects on bleeding on the rigor onset,
oxidation progress is another factor which can be reduced. It means that after
post-slaughter processes, the released haem iron (ferrous (+2)) is converted to
the ferric (+3) and start the autoxidation progress. Both haem proteins (haemoglobin
(Hb) and myoglobin) can increase the lipid oxidation in fish and other muscle
foods (Kanner, 1994). Oxidation has a negative effect on some quality parameters
such as colour, flavour and nutritional value (Kanner, 1994).  (Richards & Hultin, 2002) reported that,
the blood residue in fish fillet, catalyses lipid oxidation during storage of
fatty fish and bleeding was also shown to retard lipid oxidation of minced
trout muscle during storage at +2oC. (Maqsood & Benjakul, 2011) showed
that, the initiation and propagation of lipid oxidation in the un-bled samples compared
with the bled samples were more marked.

Furthermore, products of lipid oxidation can react
more with proteins and vice versa. The progress of oxidative reactions in foods
is additionally enhanced by the interactions between proteins and lipids due to
the similarity of the oxidation reactions. The oxidation of proteins and lipids
has similar catalysts and the processes seem to be interlinked.
For example,
during the storage of herring fillets, peroxide value (PV) and thiobarbituric
acid reactive substances (TBARS) increased while the amount of haem-proteins
decreased (Jonsson, 2007). However,
there is still little known about the interaction of protein and lipid
oxidation and the subsequent impact on muscle food quality (Baron, et
al., 2007). Secondary
products of lipid oxidation (aldehydes) can modify the stability of myoglobin
and generate adducts through a covalent modification with myoglobin. Furthermore,
metmyoglobin and H2O2, resulting from oxymyoglobin
oxidation, can provoke lipid oxidation. In one way the products of oxymyoglobin (metmyoglobin
and H2O2) are necessary to start lipid oxidation and on
the other way aldehydes can change myoglobin stability and promote oxymyoglobin
oxidation. Therefore, development of lipid oxidation and protein degradation
during post mortem changes are the most important factors that can be remarked.

Despite the knowledge generated on specific protein
degradations during post-mortem storage of fish, it is still unclear how the
degradation of specific proteins relates to fish tenderization, and
more investigations are needed.