Food Lipids: Chemistry, Nutrition, and Biotechnology

with this chemical, treated salmon and red grouper fillets had elevated levels of
oxidative products [283]. Similarly, channel catfish fillets rinsed in ozonated water
or water containing hydrogen peroxide had higher levels of oxidative products than
untreated fillets [284]. Despite the elevated levels of oxidative products in both of
these fish studies, the products were still considered acceptable. However, it is unclear
at this time whether the increased concentration of oxidative products initially
would impact the progression of lipid oxidation during storage.
B. Washing
Washing (as opposed to rinsing) is designed to remove chemical constituents of the
tissue rather than microbial contaminants. Used in the process of making surimi,
washing removes not only soluble proteins but fat, prooxidants, and antioxidants as
well. Muscle oxidative stability ultimately depends on the relative levels of these
components removed. For example, Undeland et al. [285] demonstrated that washing
removed prooxidative enzymes and low molecular weight iron and copper catalysts
from minced herring. Despite the removal of these components, however, washing
decreased the lipid stability of the product pointing to the simultaneous removal of
antioxidants. Consequently, to offset this antioxidant loss, investigators have recommended
washing in antioxidant solutions [286]. Similarly, Richards et al. [287]
demonstrated that an antioxidant wash improved the stability of mackerel fillets from
stage 1 rigor but not stage 3 rigor. The improved response by the fresher fish was
attributed to the greater removal of uncoagulated blood in those samples.
C. Skinning
Accessibility of tissues to oxygen is considered one of the most important factors
contributing to oxidative instability. While filleting of fish is a common practice, it
has been shown that the skin protects underlying areas from oxidation [34]. If the
skin has to be removed early in the processing chain, deep skinning is an alternative
to normal skinning and has been shown to improve the cold storage stability of
saithe fillets [288]. Improvement is warranted since the highest rate of oxidation is
observed in the under skin layer lipids [34].
D. Mincing
Mincing muscle tissue disrupts cellular integrity and exposes more of the lipids to
the oxidative catalysts; it also dilutes the antioxidants and increases the exposure of
the tissue to oxygen [361]. In particular, the intracellular location of the triacylglycerols
could provide protection against hydrolysis in the intact muscle; but upon
mincing, this protection is minimized if not eliminated. Mechanical disruption of the
tissue also induces membrane lipids to form much smaller vesicles, and the increased
surface area accelerates their degradation [289]. Further promotion of oxidation occurs
in mechanically deboned flesh in response to release of hemoglobin and lipids
from the bone marrow [290–292] and release of nonheme iron from the iron parts
of the deboner [290,293]. While meat grinder wear and degree of stress applied
during deboning have not led to significant variations in oxidative stability of stored
sample [293,294], the head pressure used in the mechanical deboning of roaster
breasts affected the chemical composition of the product and in turn its susceptibility
to lipid oxidation [292].
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