Food Biochemistry and Food Processing

390 Part III: Muscle Foods

contrast the authors reported that slow freezing and
fluctuations in temperature during frozen storage
were found to result in the release of acid lipase
from the lysosomes of the dark muscle of rainbow
trout.
Several researchers have reported an increase in
free fatty acids during frozen storage of muscle of
different fish species such as trout (Ingemansson et
al. 1995), salmon (Refsgaard et al. 1998, 2000), ray-
fish (Fernandez-Reiriz et al. 1995), tuna, cod, and
prawn (Kaneniwa et al. 2004). The release of free
fatty acids during frozen storage can induce changes
in texture by stimulation of protein denaturation and
through off-flavors being produced by lipid oxida-
tion (Lopez-Amaya and Marangoni 2000b). Refs-
gaard et al. (1998, 2000) observed a marked increase
in free fatty acids in salmon stored at
10 and

20°C. This increase in free fatty acid content was
connected with changes in sensory attributes, sug-
gesting that lipolysis plays a significant role in dete-
rioration of the quality of salmon during frozen stor-
age.
Kaneniwa et al. (2004) detected a large variation
in the formation of free fatty acids among nine
species of fish and shellfish stored at
10°C for 30
days. Once again, this demonstrates the large varia-
tion in enzyme activity in seafood species. Findings
of Ben-gigirey et al. (1999) indicate that the temper-
ature at which fish are stored has a clear influence on
the lipase activity occurring in the muscle. They not-
ed, for example, that the formation of free fatty acids
in the muscle of albacore tuna during storage for the
period of a year was considerably higher at
18°C
than at
25°C.
Two classes of lipases, the lysosomal lipases and
the phospholipases, are apparently involved in the
hydrolysis of lipids in fish muscle during storage.
Nayak et al. (2003) found significant differences
among four fish species (rohu, oil sardine, mullet,
and Indian mackerel) in the degree of red muscle
lipase activity. This is quite in line with differences
in lipid hydrolysis among species that Kaneniwa et
al. (2004) reported.
Although both the lipase activity and the forma-
tion of free fatty acids in fish muscle are well docu-
mented, only a few studies have actually isolated and
characterized the muscle lipases and phospholipases
involved. Aaen et al. (1995) have isolated and char-
acterized an acidic phospholipase from cod muscle,
and Hirano et al. (2000) a phospholipase from the

white muscle of bonito. Similarly, triacylglycerol

lipase from salmon and from rainbow trout has been

isolated and characterized by Sheridan and Allen

(1984) and by Michelsen et al. (1994), respectively.

Knowledge of the properties of the lipolytic

enzymes in the muscle in seafood and of the re-

sponses the enzymes show to various processing

parameters, however, is sparse. Extensive reviews of

work done on the lipases and phospholipases in

seafood has been presented by Lopez-Amaya and

Marangoni (2000a,b).

ENDOGENOUS ENZYMATIC

REACTIONS DURING THE

PROCESSING OF SEAFOOD

During seafood processing such as salting, heating,

fermentation, and freezing, endogenous enzymes can

be active and contribute to the sensory characteris-

tics of the final product. Such endogenous enzyme

activities are sometimes necessary in order to obtain

the desired taste and texture.

SALTING OFFISH

Salting has been used in many countries for cen-

turies as a means of preserving fish. Today, the pri-

mary purpose of salting fish is no longer only to pre-

serve them. Instead salting enables fish products

with sensory attributes that are sought after, such as

salted herring and salted cod, as produced on the

northern European continent and in Scandinavia.

Enzymatic degradation of muscle proteins during

salting is a factor that contributes to the develop-

ment of the right texture and taste of the products.

Ripening of Salt-Cured Fish

Spiced sugar–salted herring in its traditional form is

made by mixing approximately 100 kg of headed,

ungutted herring with 15 kg of salt and 7 kg of sug-

ar in barrels, usually adding spices as well. After a

day or two, after a blood brine has been formed, sat-

urated brine is added, after which the barrels are

stored at 0–5°C for up to a year. During this period a

ripening of the herring takes place, and it achieves

its characteristic taste and texture (Stefánsson et al.

1995).

During the ripening period, both intestinal and

muscle proteases participate in the degradation of