BLBS102-c19 BLBS102-Simpson March 21, 2012 13:33 Trim: 276mm X 219mm Printer Name: Yet to Come
354 Part 3: Meat, Poultry and SeafoodsVarious antioxidative components can be highly effective in
delaying lipid oxidation. All aquatic animals have a number of
different indigenous antioxidants, and it is important to avoid
conditions that can negatively affect or destroy these (Hultin
1994). It has been well researched and is well known that an-
tioxidants can be added to seafood during processing to increase
their oxidative stability (Fig. 19.3). Addition of antioxidants
early during processing is also important. Since many of the
prooxidants in seafood are in the aqueous phase and the lipids
constitute a nonpolar phase, a combination of polar and nonpo-
lar antioxidants has been found to be very effective. Tocopherol
(vitamin E), a nonpolar antioxidant, and ascorbate (vitamin C),
a polar antioxidant, are among the most commonly added an-
tioxidants. Sometimes, metal chelators such as EDTA are added.
However, it is worth mentioning that under certain conditions
antioxidants can act as prooxidants. For example, this is true
for ascorbic acid and EDTA, both of which can stimulate iron-
mediated lipid oxidation. For example, when the ratio of EDTA:
iron is 1, it is prooxidative, but when the ratio is .1, it is an-
tioxidative (Halliwell and Gutteridge 1989). Since ascorbate is a
reducing agent, it can also reduce iron under certain conditions
and thus make it more prooxidative (Halliwell and Gutteridge
1988).BIOCHEMICAL CHANGES IN PIGMENTS
DURING HANDLING, STORAGE, AND
PROCESSINGThe main pigments in seafood can be classified as heme proteins
(hemoglobin and myoglobin) in red-meat (warm-blooded) fish,
hemocyanin in cold-blooded shellfish such as crustaceans and
mollusks, and carotenoids in some important fish and shellfish
products. The changes during handling, storage, and processing
greatly affect the quality of these seafoods. Epithelial pigments
and carotenoids also undergo changes during postmortem ice-
chilled storage.Epithelial DiscolorationThe market value of squid is related to the contraction state of
its epidermal chromatophores, called ommochromes. In recently
harvested, prerigor squid, the pigment is dispersed throughout
the chromatophores; hence, the dark red-brown appearance of
the epithelial tissue. Following rigor mortis, the pigment cells
contract, giving the skin a pale, light coloration dotted with dark
flecks. The continued storage of squid results in a structural de-
terioration of the ommochrome membrane, leading to bleeding
of pigment and downgrading of quality. The dark brown col-
oration characteristic of very fresh squid can be retained during
processing, for example, by freezing or dehydration. However,
improper storage of frozen or dried squid will result in chro-
matophore disruption and red discoloration of the meat (Hink
and Stanley 1985).
The frozen storage of some fish may result in subcutaneous
yellowing of flesh below the pigmented skin (Thompson and
Thompson 1972). Apparently, freezing or other processes that
disrupt chromatophores can lead to the release of carotenoidsand their migration to the subcutaneous fat layer. Subcutaneous
yellowing that occurs during the prolonged storage of frozen fish
can originate from other causes, that is, yellowing associated
with lipid oxidation and carbonyl-amine reactions.HemoglobinNormally, hemoglobin contributes less to the appearance of
seafood than myoglobin because it is lost easily during han-
dling and storage, while myoglobin is retained in the intracellu-
lar structure. The amount of hemoglobin present also affects to
a greater extent the color appearance of light red and dark red
muscles of red-meat fish flesh (Wang and Amiro 1979). For ex-
ample, in yellowfin tunaNeothunnus macropterus, hemoglobin
concentrations ranged from 12 to 50 mg% in light red muscle
and 50 to 380 mg% in dark red muscle (Livingston and Brown
1981). The amount of residual hemoglobin in fish muscle is ob-
viously influenced by the bleeding efficacy at the time of catch.
Method of catch also affects the residual hemoglobin in the fish
muscle. For example, the percent of total heme as hemoglobin
in the meat of yellowfin caught by bait boat and purse seine was
24% and 32%, respectively (Barrett et al. 1965).
The green meat of raw or frozen broadbill swordfish (Xiphias
gladus) is believed to be due to the combination of hemoglobin
with hydrogen sulfide generated from the fairly extensive de-
composition of the meat (Amano and Tomiya 1953).HemocyaninHemocyanin, not hemoglobin, is present in the blood of shell-
fish, that is, crustaceans and mollusks. Hemocyanins are copper-
containing proteins, as compared with iron-containing proteins
in hemoglobins, and they combine reversely with oxygen. The
contribution of hemocyanins to seafood quality is not very well
understood. It is suspected that the blue discoloration of canned
crabmeat is associated with a high content of hemocyanin. The
average copper content of blue meat (e.g., 2.8 mg%) is higher
than meat of normal color (e.g., 0.5 mg%) (Ghiretti 1956).MyoglobinMyoglobin in fish muscle is retained in the intracellular structure.
In fish muscle, the red, white, and intermediate fibers tend to be
more distinctively segregated than they are in muscle from land
animals. The myoglobin content in muscle of yellowfin tuna
was found to range from 37 to 128 mg% in the light-colored
muscle and from 530 to 22,400 mg% in the dark-colored muscle
(Wolfe et al. 1978). In cod, the deep-seated, dark-colored mus-
cle is richer in myoglobin than superficial dark-colored muscle
(Brown 1962, Love et al. 1977).
Myoglobin in fish is easily oxidized to a brown-colored met-
myoglobin. The discoloration of tuna during frozen storage is
associated with the formation of metmyoglobin, depending on
temperature and location (Tichivangana and Morrissey 1985).
Greening is a discoloration problem associated with cook-
ing various tunas. The problem arises from the formation of a
sulfhydryl adduct of myoglobin in the presence of an oxidizing