BLBS102-c19 BLBS102-Simpson March 21, 2012 13:33 Trim: 276mm X 219mm Printer Name: Yet to Come
19 Biochemistry of Seafood Processing 353Figure 19.3.Effect of absence or presence of antioxidants (AO) on the oxidative stability of washed dark and white mackerel muscle during
frozen storage (220◦C). The antioxidant TBHQ was added during grinding, while ascorbate and EDTA were added during grinding and
washing. (Adapted from Kelleher et al. 1992.)Novel processing methods such as irradiation and high-
pressure processing have been reported to lead to increased
levels of lipid oxidation. High-pressure treatment has been re-
ported to have relatively small effects on purified lipids from
fish, while high-pressure treatment of fish muscle leads to
high levels of lipid oxidation products (Ohshima et al. 1993a).
This increase in oxidation is hypothesized, in part, to be via
pressure-induced denaturation of heme proteins, which are po-
tent prooxidants (Yagiz et al. unpublished data). Increased pres-
sure and time also appears to lead to increased oxidation. Lipid
hydrolysis has been found to be increased by medium lev-
els of pressure, while it is reduced at high pressures, likely
due to lipase inactivation (Ohshima et al. 1993b). Several
studies have been conducted on the effect irradiation has on
seafood quality, although this process is not allowed in many
countries. It has been observed that low doses of gamma ir-
radiation (5 kGy) may have an accelerating effect on the
oxidative instability of some fish species and not others dur-
ing postirradiation refrigerated storage. Al-Kahtani et al. (1996)
reported that irradiation (1.5–10 kGy) led to more oxidation in
tilapia and Spanish mackerel during refrigerated storage than
in untreated fish. Fatty acid changes were also observed in that
study. The likely cause for increased lipid oxidation on irra-
diation is the formation of radicals, more at higher levels of
irradiation.Minimization of Lipid-Derived
Quality ProblemsTo maintain or extend the sensory and nutritional qualities of
seafood, it is important to minimize or delay the undesirable
reactions of lipids, such as oxidation and hydrolysis. Time
is of the essence with these reactions, and thus interventionsshould be done as early as possible to be able to extend
quality as much as possible. The simplest means of controlling
oxidation is maintaining low temperatures, since enzymatic
and nonenzymatic oxidation reactions are greatly influenced
by temperature (Hultin 1994). As mentioned before, very low
temperatures such as freezing will accelerate lipid hydrolysis.
However, hydrolysis as well as oxidation will be reduced if
products are kept at extremely low frozen storage temperatures
(e.g., below− 40 ◦C) compared with conventional frozen storage
(about− 20 ◦C or higher).
At the harvest level, bleeding fish can lead to significantly
lower levels of oxidation, since heme proteins are reduced
(Richards et al. 1998). Special care should be taken to prevent
tissue disruption in storage, since both oxidation and hydrolysis
will be increased. Washing fish fillets and fish mince will also
remove significant amounts of heme proteins (Kelleher et al.
1992, Richards et al. 1998). Another effective way to reduce oxi-
dation of unstable species is the removal of dark muscle, or deep
skinning. This removes not only a large fraction of the heme
proteins but also a large amount of oxidatively unstable lipids
present in the dark muscle itself and below the skin. Protection
from oxygen is another effective means for reducing oxidation.
This can be achieved through modified atmosphere packaging,
where oxygen is either reduced (for lean species) or completely
removed (for fatty species). Vacuum packaging of seafood is also
highly effective for reducing oxidation (Flick et al. 1992). Fil-
leting fish under water (where O 2 is low) has also been reported
to lead to less oxidation on storage than filleting in air (Richards
et al. 1998). Special gases such as carbon monoxide have been
found to significantly reduce oxidation of several species, even
after fillets are removed from the gas, most likely since the gas
reduces the prooxidative activities of heme proteins (Kristinsson
et al. 2003).