BLBS102-c19 BLBS102-Simpson March 21, 2012 13:33 Trim: 276mm X 219mm Printer Name: Yet to Come
19 Biochemistry of Seafood Processing 351Figure 19.1.Seasonal variation in the fat content in different parts of Atlantic mackerel. (Adapted from Leu et al. 1981.)decrease the level of unstable fatty acids to increase the shelf life
of the product. A good example is catfish (Table 19.6), which
in the wild has more unstable (but more nutritionally beneficial)
fatty acids than grain-fed aquacultured catfish (Angelo 1996).Table 19.6.Fatty Acid Composition of Extracted Lipids
from Wild and Pond-Reared Channel CatfishFatty Acids Wild (%) Pond-Reared (%)16:0 20.63 19.62
16:1v7 7.48 4.15
18:0 8.04 6.67
18:1v 23.72 42.45
18:2v6 2.9 12.35
18:3v3 2.78 1.66
18:4v3 0.6 0.96
20:1v9 0.83 0.97
20:3v6 0.36 0.98
20:4v6 6.82 1.88
20:4v3 0.62 0.16
20:5v3 7.02 1.49
24:1v9 0.34 0.16
22:4v6 0.68 0.14
22:5v6 1.34 0.51
22:5v3 3.05 0.98
22:6v6 13.56 4.97
Saturated 28.67 26.28
Monounsaturated 31.64 47.64
Polyunsaturated 39.77 26.07
v-6 PUFA 12.13 15.85
v-3 PUFA 27.64 10.22
v3/v6 2.54 0.62Source: Adapted from Chanmugam et al. (1986).Although varying levels of total fat content in fish can influ-
ence quality, fatty acid type rather than quantity appears to be
more important. The major classes of lipids in fish are triglyc-
erides and phospholipids. Triglycerides, the majority of lipids
in fish (except very lean fish), are neutral lipids. They exist as
either large droplets within the adipose tissue or smaller droplets
between or within muscle cells (Undeland 1997). These lipids
are deposited and stored as an energy source for fish (Huss
1994). The phospholipids, which are polar lipids, are one of the
main building blocks of muscle cell membranes and are usu-
ally present only at low levels, 0.5–1.1% (O’Keefe 2000). Some
muscles of very lean species such as cod, pollock, and whiting
can contain less than 1% lipids, most of which are in the form
of membrane phospholipids.
Compared with other animals, aquatic animals are especially
rich in long-chain PUFAs, which are found in higher numbers
in the membrane phospholipids than in storage triglycerides
(Hultin and Kelleher 2000). Aquatic animals adapted to cold
water also have higher levels of PUFAs than those adapted to
warmer waters, since more unsaturation is essential to main-
tain membrane fluidity and function at low temperatures. It has
been reported that about half of the membrane phospholipids in
cold-water fish are the omega-3 fatty acids eicosapentoic acid
(20:5v3) and DHA (22:6v3) (Shewfelt 1981). These fatty acids
have been found to be highly active physiologically, for exam-
ple, leading to decreased plasma triacylglycerols, cholesterol,
and blood pressure (Wijendran and Hayes 2004) and modu-
lating immunological activities (e.g., inflammation) (Klurfeld
2002), to name a few important functions.Lipids and Quality ProblemsEven though the phospholipids are at very low levels compared
to neutral fats, they are believed to lead to more quality prob-
lems such as lipid oxidation, which is a major cause of quality