BLBS102-c19 BLBS102-Simpson March 21, 2012 13:33 Trim: 276mm X 219mm Printer Name: Yet to Come
356 Part 3: Meat, Poultry and Seafoodsdeterioration or mishandling. It was demonstrated that the ap-
pearance of honeycombing was related to collagen degradation
(Frank et al. 1984). Mackerel was also shown to develop hon-
eycombing when poorly handled (Pan et al. 1986). Freshwater
prawn developed mushiness rapidly due to poor handling after
catch. It was also demonstrated that this mushiness problem was
related to collagen degradation (Nip et al. 1985). It should be
noted that all these problems are observable only after the fish or
prawn have been cooked and are only detected visibly. It is be-
lieved that these problems developed before bacterial spoilage
of the fish. Analysis of collagen degradation is also tedious,
involving hydrolysis of the extracted collagen and analysis of
hydroxyproline.Dimethylamine FormationTMAO is commonly found in large quantities in marine species
of fish, especially the elasmobranch (Jiang and Lee 2004) and
gadoid (Bonnell 1994) species. After death, TMAO is readily
degraded to DMA through a series of reactions during iced and
frozen storage. DMA is typically observed in frozen gadoid
species such as cod, hake, haddock, whiting, red hake, and
pollock (Castell et al. 1973). TMAO degradation with DMA
formation was enhanced by the presence of an endogenous en-
zyme (TMAOase) in the fish tissues, as observed in cod muscle
by Amano and Yamada (1965). It should be noted that TMAO
degradation can also be bacterial. Readers should consult the
reviews by Regenstein et al. (1982), Hebard et al. (1982), Hultin
(1992b), or other literature elsewhere.Free Fatty Acid AccumulationPostmortem lipid degradation in seafood, especially fatty fish,
proceeds mainly due to enzymatic hydrolysis, with the accumu-
lation of FFAs. About 20% of lipids are hydrolyzed during the
shelf life of iced fish. The amount of FFAs is more or less dou-
bled during that period, mostly from phospholipids, followed
by triglycerides, cholesterol esters, and wax esters (Haard 1990,
Sikorski et al. 1990b).Tyrosine AccumulationThe accumulation of lactic acid accompanied with a drop in
pH causes the liberation and activation of inherent acid cell
proteases, cathepsins (Eskin et al. 1971). Tyrosine has been
reported to accumulate in stored fish due to autolysis. Its use
as an index of freshness has been proposed by Shenouda et al.
(1979) because of its simplicity in analysis. However, it was
shown that the pattern of tyrosine accumulation was similar to
that of the TVB, an indicator of bacterial spoilage. Therefore,
its use as a biochemical index (before bacterial spoilage) is not
sufficiently sensitive and specific enough to assess total fish
quality (Simpson and Haard 1984).BIOCHEMICAL AND
PHYSICOCHEMICAL CHANGES
IN SEAFOOD DURING FREEZING
AND FROZEN STORAGEFreezing is widely used to preserve and maintain the quality of
food products for an extended period of time because microbial
growth and enzymatic and biochemical reactions are reduced at
low temperatures. However, ice crystals formed as a result of
freezing may damage cells and disrupt the texture of food prod-
ucts, and the concentrated unfrozen matrix may result in changes
in pH, osmotic pressure, and ionic strength. These changes can
affect biochemical and physicochemical reactions such as pro-
tein denaturation, lipid oxidation, and enzymatic degradation of
TMAO in frozen seafood. Therefore, it is essential to understand
these reactions in order to extend the shelf life and improve the
quality attributes of seafood.Protein DenaturationDuring freezing or frozen storage, changes in the physical state
of water and the presence of lipids create an environment that in-
duces protein denaturation. This denaturation can be caused by
one or more of the following factors: (1) ice crystal formation,
(2) dehydration effect, (3) increase in solute concentration, (4)
interaction of protein with intact lipids and FFAs, and (5) inter-
action of protein with oxidized lipids (Shenouda 1980). Denatu-
ration of protein changes the texture and functional properties of
protein. The texture of fish may become more fibrous and tough
as a result of the loss of protein solubility (Benjakul and Sut-
thipan 2009, Reza et al. 2009) and water-holding capacity. For
example, the gel strength of rainbow fish (Trichiurus savala)pro-
tein significantly decreases after 100 days of storage at− 20 ◦C
(Mishra and Dora 2010). These textural changes as a result of
protein changes give rise to undesirable sensory attributes, which
are often described as sponginess, dryness, rubbery texture, and
loss of juiciness (Haard 1992a). Tseng et al. (2003) suggested
that to retain good eating qualities, that is, to maintain tenderness
and cooking yield, and reduce lipid oxidation, red claw crayfish
(Cherax quadricarinatus) should not be subjected to more than
three freeze-thaw cycles.Ice Crystal EffectIce may form inter- and intracellularly during freezing, which
ruptures membranes and changes the structure of the muscle
cells (Mazur 1970, 1984, Friedler et al. 1988). At a slow freezing
rate, fluids in the extracellular spaces freeze first, thus increas-
ing the concentration of extracellular solutes and drawing water
osmotically from the unfrozen cell through the semipermeable
cellular membrane (Mazur 1970, 1984). The diffusion of water
from the internal cellular spaces to the extracellular spaces re-
sults in drip, collected from frozen muscle tissues when thawed
(Jiang and Lee 2004). Drip contains proteins, peptides, amino
acids, lactic acid, purines, vitamin B complex, and various salts
(Sulzbacher and Gaddis 1968), and their concentration in drip
increases with storage time (Einen et al. 2002). On the other