Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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some directed fishery such as a trawling, longline,

treknetting, or seining industry. Where elasmobranch

fishing is directed, use is made of lines (even hand-

lines) and hooks.

Commercial Products Derived from

Elasmobranch Species

Shark and Ray Flesh (Fresh, Chilled, or Frozen)

0005 The smaller species of shark are generally used as

sources of fresh, chilled, or frozen meat, while the

larger sharks provide fins and hides. In the world

context, the spotted spiny dogfish (Squalus

acanthias), which grows to a length of 1 m and

which, unlike most other sharks, is readily skinned,

constitutes the major source of shark meat. The rela-

tively small smooth houndstooth sharks (Mustelus

canis, M. manazo, and M. mustelus), the blue shark

(Prionace glauca, which grows to almost 4 m in

length), the porbeagle (Lamna nasus, which reaches

3 m in length), and the mako shark (Isurus glaucus,of

similar potential size as the porbeagle) are also im-

portant sources of shark meat. However, in the case

of larger specimens of these species, the flesh would

be used mainly as an ingredient of fish pastes, or sold

as steaks, or included in smoked or minced form of

bacalao. In Japan the flesh of the porbeagle, the

gummy shark (Mustelus spp.), and the whiptail ray

(Dasyatis akajei) are the only elasmobranch species

readily eaten as fresh fish. It is reported that these

species do not acquire an ammoniacal taste shortly

after being caught.

0006The elephantfish (Callorynchus spp.) is a source of

particularly fine flesh of a good white color which,

like the flesh of some noncartilaginous fish, is lean.

The low-fat content has consumer appeal in countries

where there is an awareness of the detrimental effect

of a high-fat intake. Low-fat levels of 0.1–0.3% are

recorded in the flesh of various shark species. Low

muscular fat levels are usually associated with high

levels of fat storage in the liver; also in noncarti-

laginous fish. Certain of the smaller Carcharhinus

species are of importance in some areas, e.g., the

black-tipped shark (C. limbatus or C. johnsoni)and,

in Italy and France, even the large dusky shark

(C. obscurus) has importance. The tiger shark (Galeo-

cerdo cuvieri), which grows to a very large size, is

used as a source of shark flesh in several areas of

the world. The thresher shark of the Caribbean (Alo-

pias vulpinus) is a large shark: it’s meat is perceived

to be of very good quality and is said to resemble

swordfish.

0007In Japan, it appears that little shark flesh is eaten

as fillets or cutlets, but shark flesh has found its way

into what might be called surimi-based products. For

this purpose certain gel-forming properties are re-

quired. Of the major species mentioned above, three

appear to have found use in chikuwa and kamaboko-

type products: Prionace glauca, Mustelus manazo,

1. Dorsal fin spine.

2. First dorsal fin.

3. Second dorsal fin.

4. Notch at caudal base above.

5. Upper caudal lobe.

6. Lower caudal lobe.

7. Notch at caudal base below.

8. Anal fin.

9. Pelvic fin.

10. Clasper of male.

11. Pectoral fin.

12. Gill-slits.

13. Mouth.

14. Nostril.

15. Snout.

16. Nictitating membrane.

17. Spiracle.

18. Peduncular keel.

19. Lower lip.

20. Lower labial fold.

21. Upper lip.

22. Nasal flap.

23. Nasal cirrus.

fig0001 Figure 1 Most of the features of a typical chondrichthyan fish. Not all of these features are found in any one fish.

2448 FISH/Important Elasmobranch Species

and Isurus glaucus. Shark flesh is not necessarily

used on its own in these products, but rather as a

substitute for traditional white fish types. Lamna

nasus and Prionace glauca are said to produce weak

(nonelastic) gels, but the flesh of most sharks and

rays has good elastic properties. Good gel-forming

is associated with a high myosin content, myosin

being that portion of the muscular protein that

solubilizes in 1.2–1.5 mol l

1

sodium chloride so-

lution.

0008 As far as skates, stingrays, and guitarfish are con-

cerned, there is no indication that specific species are

more suitable for certain products. Whole gutted

skate and skate wings, skin-on or skinned, and skate

nobs (chunks of flesh), used fresh and in the frozen

form, are world trade commodities. Stingrays are sold

alive or fresh in Japan. In as far as rays tend to be

more limited in distribution than sharks, there is a

tendency for some species of rays to predominate in

the catch from specific areas.

0009 The flesh of skates and rays passes through rigor

mortis more rapidly than that of cod, for example,

and it is not inclined to suffer from the gaping

phenomenon that occurs in some fish fillets.

0010Of 16 shark species studied as a source of flesh,

some of the better known species have high fillet

yields, in excess of 45% of the original body mass.

These include Squalus acanthias, Mustelus manazo,

and Carcharinus falciformis. The yield of the

hammerhead shark (Sphyrna tudes), at 54.4%, is

almost as high as the best, i.e., the blacktip shark

(C. limbatus).

Canning of Shark Flesh

0011Some years ago a small shark-canning industry was

set up in Murmansk, a port on the Barents sea.

Smoked and Salted and/or Dried Flesh of Sharks

and Rays

0012Flesh of the shark species listed above is smoked and

salted and/or dried in various countries. Some of the

larger sharks appear to be only used in this manner.

The hammerhead sharks (Sphyrna tudes and S.

zygaena), which are not favored as a source of fresh

meat, are used for the production of salted and

dried meat in the Caribbean and South America. A

notable exception is schillerlocken, a smoked product

tbl0001 Table 1 Products (t) derived from sharks, skates, and rays produced by different countries during 1989

Country Fresh or

chilled fillets

Frozen fillets Frozen sharks Sharks dried,

salted, orinbrine

Sharks, rays, etc.

(driednotsalted)

Shark fins

(dried, notsalted)

Shark fins

(driedand salted)

Chile 234

China 563

Colombia 645

Denmark 1 55

Faroe Islands 340

Fiji 14

Greece 100

India 190

Indonesia 475

Ireland 134

Italy 1500

Japan 10 015

Korea 36

Maldives 13

Mexico 3224

New Zealand 19 479 969

Norway 105

Pakistan 5250 317

Peru 518 678 1326

South Africa 660

Sri Lanka 221 54

Thailand 1000

2500

UK 1108

USA 1068 1518

Uruguay 4 4

Yemen 60

Unidentified 1179

Represents Food and Agriculture Organization (FAO) estimate from sources available to the FAO. Data from FAO (1991b) Fisheries Statistics

Commodities. FAO Yearbook. FAO Fisheries Series 37, FAO Statistics Series 101. Rome: Food and Agriculture Organization.

FISH/Important Elasmobranch Species 2449

produced in Germany from the belly flaps of a small

shark, the dogfish; in addition, some smoked shark

delicatessen products are made in Italy from shark of

popular species and size. Shark flesh appears to be

consumed primarily in salted form in some South and

Central American countries, but it is also used in the

fresh or chilled form and for freezing.

0013 The flesh of the ray is hot-smoked, while a fer-

mented product, subsequently salted, is made in Ice-

land. Rays of the genus Gymnura (a butterfly ray) are

dried (unsalted) in Indonesia, while the ray is also

used in this manner in Gambia, and guitarfish

are dried and salted in India. (See Smoked Foods:

Principles; Applications of Smoking.)

Mercury and Ammonia Formation in Shark

Flesh

0014 There are two aspects which cannot be ignored in

a discussion on the use of the flesh from different

cartilaginous fish. The first is the mercury content

of the flesh of sharks, which is sometimes raised,

and the second is the postmortem formation of

ammonia.

Mercury Content

0015 Relatively high contents of mercury, up to about

8mgkg

1

of flesh, have been recorded in shark

flesh, while values of up to 1 mg kg

1

are on record

for skates, and 0.3 mg kg

1

for chimeras (Callo-

rynchus spp.). This chemical property is shared with

other long-living, wide-ranging finfish such as sword-

fish and marlins. Cartilaginous fish, however, often

contain very low levels of mercury. In one particular

laboratory the mercury contents of 1003 samples of

Isurus glaucus, measured as total mercury, ranged

from 0.02 to 8.29 mg per 100 g, with a mean of

0.54 mg per 100 g of flesh, while 163 samples of

Galeorhinus galeus yielded 0.2–3.75 mg per 100 g

of flesh (mean of 0.88 mg).

0016 Maximum limits for the mercury content of flesh –

operative in the world fishery market at present – lie

between 0.5 and 1 mg kg

1

of flesh. As these animals

are generally quite mobile, i.e., not restricted to nar-

rowly defined geographic areas, one expects that the

age of the fish would be the major determinant of the

level of mercury that will have been taken up and

retained by the body. This great mobility is thought

to be one of the reasons for the high mercury content

of shark flesh; they take in more water than would a

slower-moving fish of similar size. Also, for reasons

not understood, sharks secrete the heavy metal at a

lower rate than they take it up. (See Mercury: Proper-

ties and Determination; Toxicology.)

Ammonia Formation

0017While ammonia production owing to bacterial action

is a common feature of fish flesh, the effect is exagger-

ated in the flesh of cartilaginous fishes. These fish

possess, in addition to the trimethyl amine oxide of

fish blood and muscle, a further nitrogen-rich com-

pound, urea (carbonyl amide), which functions in

osmoregulation to maintain the fish in balance with

its salt-water environment. Bacteria that come in con-

tact with the blood or flesh of the fish after death

break down these compounds to release amines and,

in the case of urea, ammonia with its characteristic

pungent ‘fishy’ smell; the release of ammonia is a first

step in the breakdown process, resulting from bacter-

ial urease activity. (See Amines.)

0018Bleeding of sharks is recommended as soon as pos-

sible after death, a step which is not practiced in some

of the Squalus acanthias fisheries – hence the reddish

color of the flesh in such cases. Rapid cooling by icing

or freezing and strict hygiene are further recom-

mended practices. Urea can also be removed by leach-

ing with water or brine, while in the case of salted,

dried flesh the urea content will have been reduced.

Even if no bacterial action takes place during the

earlier stages of salting which will result in urea

breakdown, the leaching effect which accompanies

salting results in considerable loss of urea from the

flesh.

0019The urea contents of the flesh differ between

and within species. According to one source, Squalus

acanthias lies at the low end of the range with

1570 mg urea per 100 g of flesh and smooth hammer-

head shark (Sphyrna zygaena) is at the higher end

with 2038 mg per 100 g. Skate fall in the same class

as sharks in terms of their urea content, in the range

1–2%. The few values available for St Joseph shark

range from 1.4% to 1.8%.

Utilization of Shark Fins for Soup

0020One set of shark fins usually consists of two pectoral

fins, the first dorsal fin (and in large sharks with two

dorsal fins, the second) and the lower lobe of the

tail fin. These fins are either dried or salted and

dried and used in the Orient and by Chinese commu-

nities elsewhere to produce shark fin soup. Small

sharks do not yield suitable fins, while some larger

species do not produce fins of desirable quality. In

general, however, the fins of any shark longer than

1.5 m can be used.

0021Of the sharks of suitable size, only nurse shark

(Ginglymostoma cirratum) fins and the sawshark

(Pristiphorus mudipiunis) pectoral fins appear to be

of no commercial value.

2450 FISH/Important Elasmobranch Species

0022 The preferred shark species are the hammerhead,

the mako, and the blue, mentioned above, and the

tope or soupfin, Galeorhinus galeus. Fins from many

of the large and the very large sharks are used, how-

ever, including those of the great white shark (Car-

charodon carcharias), the fibrous meat of which,

incidentally, is eaten in part of northern Japan. The

very large tiger shark (Galeocerdo cuvieri) is also

listed as a source of good-quality shark meat. Several

Carcharinus species provide fins for processing in

Pakistan.

Shark Hides for Leathermaking

0023 Shark skins used for leathermaking must be re-

moved from the fish in a very fresh state. Only

sharks larger than 1.5 m are skinned for leather,

with the exception of the small Pacific Ocean shark

species, the brown cat shark (Apristurus brunneus),

the hide of which is used to prepare the special boroso

leather.

0024 The nurse shark (Ginglymostoma cirratum) is the

species of first choice, except in Japan, where prefer-

ence is for the skin of the blue shark (Prionace glauca)

and that of members of the Rhinobatidae family

(guitarfish) which have relatively small skin dentiles.

These species do not produce suitable hides as far as

the shark leather industry of the USA is concerned. In

the USA the tiger shark is seen as having a good hide.

If properly cut and prepared, however, the hide from

any other larger shark species is acceptable. This

situation prevails since technical advances in shark

hide tanning were made by the Ocean Leather

Corporation of Newark in New Jersey, USA. These

advances permitted the production of softer leather

rather than the rough sandpaper-like skins produced

earlier from shark skin.

0025 The Food and Agriculture Organization has drafted

a code of practice for the utilization of sharks for food

and for skin production.

Sharks’ Teeth

0026 Sharks’ teeth represent another potential product,

similar to leather, in the sense that the end products

are consumer goods. There is at present no estab-

lished market for sharks’ teeth, except on a small

scale in some holiday resort areas, where mako

shark teeth are sought after as tourist items.

Other Products

0027 Other shark products that remain to be discussed

represent the result of further extensive processing

or are a nutrient source or products with pharmaceut-

ical or other uses.

The Japanese Product Meikotsu

0028The soft cartilage of shark or skate is diced, boiled,

and cooled in water, the remaining muscle and hard

cartilage are removed, and the soft cartilage is again

boiled and then sun-dried. This product is made in

Japan for export to China. Shark cartilage in powder

or tablet form is available for treatment of various

cancers and autoimmune conditions such as arthritis.

While there is strong evidence of dramatic beneficial

effects in some instances, the medical fraternity seems

to be skeptical.

Extraction of Chondroitin

0029Chondroitin is extracted from the hard and soft

cartilage of the shark. The chondroitins are muco-

polysaccharides composed of glucuronic acid and

galactosamine units.

0030Shark corneas have been used to implant on to

human eyes, at least in the USA and Australia.

Shark Liver Oil, Vitamins A and D, and Squalene

0031Shark flesh is virtually free of oil. On the other hand,

the livers can contain high but variable levels of oil.

The size of the livers varies greatly with the species;

larger sharks tend to have larger livers while within

species heavier sharks have relatively larger livers.

(See Fish Oils: Dietary Importance.)

0032The liver constitutes about 17.5% of the mass of

the large tiger shark (Galeocerdo cuvieri), against

2.9% of that of the soupfin shark, in this instan-

ce Galeorhinus japonicus. Some deep-water dogfish

sampled in Australia contain relatively large livers.

For the Portuguese shark (Centroscymnus coelolep-

sis) a mean of 27% of body mass was recorded and

for the leafscale gulper shark (Centrophorus squamo-

sus) 23%. There is seasonal variation in the relative

liver mass and oil contents of the livers, with an upper

limit of liver mass in the large sharks about 20% of

the body mass.

0033Marine oils are usually used as raw materials

for products such as baking fats and margarines.

The oil of the cartilaginous fish is often not made

up predominantly of triacylglycerols. The fatty acids

in such nontriacylglycerol-rich oils are associated

with diacyl glyceryl esters which may contribute

considerably to the nonsaponifiable fraction of

such oil.

0034The fatty acid composition of shark oils is not well

documented in modern literature. Oil of the head

or the liver of the spotted spiny dogfish (Squalus

acanthias) has a relatively low content of saturated

FISH/Important Elasmobranch Species 2451

fatty acids in comparison with most fish oils, i.e.,

20% or less, and high levels of C

and C

highly

unsaturated fatty acids. Head oil, for example, was

reported to contain 10.4–15.5% eicosapentaenoic

acid and 17.7–21.8% docosahexaenoic acid, the

two fatty acids claimed to be dietary essentials.

Amongst the best defined actions of these fatty acids

in the human body are reduced blood pressure, thin-

ning of the blood, reduced blood triacylglycerol levels

and brain development and visual acuity in very

young children. An oil (probably a body oil) from

the porbeagle (Lamna cornubica) contained an even

lower level of fully saturated fatty acids and a higher

level of docosahexaenoic acid. The monoenoic fatty

acid content of this oil was lower than that of

the dogfish head oil (45–47%). Also, the liver of the

dogfish is rich in monoenoic acid compared with the

oil from the flesh of the same fish. Three elasmo-

branch species (Carcharias melanopterus 31%,

Galeocerdo cuvieri 40%, and Pristis cuspidatus

37%, of the Rajiformes order) are listed as having

oils with a high content of saturated fatty acids. (See

Fatty Acids: Dietary Importance.)

0035 Interest in shark oils lies not in the fatty acids of

which the oils are composed, but primarily in the fact

that some of the oils contain high levels of vitamin A

and others high levels of a long-chain hydrocarbon

called squalene.

0036 The kitefin (Dalatius liche) and hammerhead

(Sphyrna tudes) sharks with their large livers yield

oil with high vitamin A potency, while the liver oil

of the relatively small blacktip shark (Carcharinus

limbatus) also has a high vitamin content. These vita-

min contents are higher than those of other somewhat

larger species of the same genus: C. obscurus (dusky

shark), C. plumbeus (sandbar shark), C. falciformis

(silky shark), C. leucas (bull or Zambezi shark),

C. brevipinna (spinner shark) and C. taurus (sand

shark, Taiwan). Smooth houndstooth shark (Muste-

lus manazo) and mako shark (Isurus glaucus) oils

are also high in vitamin content, as are oils from the

black shark (Galeus glaucus) and the soupfin shark

(Galeorhinus japonicus and G. galeus). The vitamin

content values are reportedly up to 100 000 IU of

vitamin A per gram of dogfish oil and even up to

156 000 IU in oil from the liver of adult G. galeus.

In general, values are only about 10% of these, with

much lower values (< 100 and 180 IU) reported for

the basking shark (Cetorhinus maximus) and the chi-

merid Hydrolagus colliei (ratfish). Compared with

the liver oils of most finfish, the elasmobranch oils

contain very low levels of vitamin D: 1 IU g

1

for the

above-mentioned ratfish to 25 IU g

1

for the oil from

the liver of the skate, Raja inornata.(See Retinol:

Physiology.)

0037The importance of natural vitamin-rich oils in the

diet of humans and farm animals has declined greatly

since the last world war as a result of the successful

synthesis at competitive costs of synthetic vitamins A

and D. The focus of the shark oil market has therefore

moved to Japan and some western countries, where

squalene is extracted from suitable shark oils. After

hydrogenation of the almost fully saturated hydro-

carbon (C

) to squalane, this material is used as

an ingredient of cosmetics. (See Cholecalciferol:

Physiology.)

0038Elasmobranch oils have been classified into three

groups on the basis of their content of unsaponifiable

matter. The first group is similar to the majority of

finfish oils, in the sense that they have a low nonsa-

ponifiable material content, i.e., up to 2%. In these

oils, cholesterol would be the major nonsaponifiable

material. The second class of elasmobranch oils

contains 10–35% nonsaponifiable material which,

in addition to cholesterol, largely consists of long-

chain alcohols naturally present as diacyl glycyl

esters. Ratfish oil is in this category. The third group

is the high-squalene group. The nonsaponifiable

material of the liver oils from the sharks in this

group is obviously high.

0039The basking shark (Cetorhinus maximus) is one of

the sharks of which the liver oil contains the highest

content of squalene, i.e., 45–75% expressed as

unsaponifiable matter (another source gives a range

of 22.8–55.3%). Deep-sea shark species which have

oils with very high unsaponifiable matter contents are

Squalus mitsukurina, Centrophorus squamosus, C.

calceus, C. acus, C. atromarginatus, C. lusitanicus,

and C. niaukang. The cosmopolitan kitefin or seal

shark (Dalatias licha) is also said to produce oil

with a very high content of unsaponifiable matter.

0040A small amount of shark oil is traded in view of its

use in industry. Special physical properties of such oils

render them suitable for use as additives in certain

lubricants and polishes.

See also: Amines; Cholecalciferol: Physiology; Fatty

Acids: Dietary Importance; Fish Oils: Dietary

Importance; Mercury: Properties and Determination;

Toxicology; Retinol: Physiology; Smoked Foods:

Principles; Applications of Smoking

Further Reading

FAO (1991a) Fishery Statistics: Catches and Landings.FAO

Yearbook. FAO Fisheries Series 36, FAO Statistics Series

98. Rome: Food and Agriculture Organization.

FAO (1991b) Fisheries Statistics: Commodities. FAO Year-

book. FAO Fisheries Series 37, FAO Statistics Series 101.

Rome: Food and Agriculture Organization.

2452 FISH/Important Elasmobranch Species

FAO (1991c) Draft Code of Practice for the Full Utilization

of Sharks. FAO Rome December 1991. FAO Fisheries

Circular 844. Rome: Food and Agriculture Organiza-

tion.

Kreuzer R and Ahmed R (1978) Shark Utilization and

Marketing. Rome: Food and Agriculture Organization.

Lane IW and Comac I (1996) Sharks Still Don’t Get Cancer.

New York: Avery.

Smith M and Hiemstra C (eds) (1986) Smith’s Sea Fishes.

Grahamstown, South Africa: JLB Smith Institute of

lchthyology.

Processing

M W Moody, Louisiana State University, Baton Rouge,

LA, USA

Introduction

0001 From earliest recorded history, humans have used fish

and fishery products for sustenance, recreation, and

many other positive aspects of developing society.

Today, fish – and the associated fish-processing indus-

try – remains an important economic segment of

nearly every modern culture. Countries controlling

water and coastal resources vehemently protect their

interest. So sensitive are the issues of fisheries man-

agement and harvesting rights that disputes have been

the source of international conflicts, embargoes, and

even wars.

0002 There are hundreds of species of fish. Nearly every

large body of environmentally sound water, both

fresh and salt, is currently producing or has the po-

tential to produce commercially important fishery

products. Although most of the fishery resource is

harvested from wild stocks, aquaculture is becoming

increasingly important as a stable and reliable source

of fin fish. Worldwide landings of fin fish approach

122 million metric tons. In 1996, the top fish-

producing countries were China, Peru, and Chile.

China alone harvested more than 33 million metric

tons of fish, more than 25% of world production.

Because of the great diversity and distribution of

fishery stocks and specific consumer demand for

processed-fish products, the international trade of

processed fishery products is significant. The esti-

mated annual per-capita world consumption of fish

and shellfish (estimated live-weight equivalent) for

human food is an estimated 15.2 kg.

0003 This article reviews the basic concepts of basic fin

fish processing and associated quality considerations.

0004Fin fish can be processed into human food, animal

food, or into components for industrial applications.

Such inherent characteristics as oil content, flesh

color, bones, size, and unit cost will usually determine

the suitability for the final product.

Onboard Handling

0005Fin fish are harvested by various capture methods,

including nets, trawlers, seines, traps, and hook and

line. In many cases, regulations will dictate approved

methods if conservation is an issue. The degree that

fish are properly handled or mishandled at the

time of capture will directly affect the quality of the

final processed product. Fish should be quickly and

thoroughly chilled and properly stored prior to

processing.

0006Most fish are initially landed on to fishing vessels

for temporary storage and transport to shore process-

ing facilities. Depending upon time and distance, the

fish may be iced, chilled, or frozen. In some instances,

the harvesting vessel is designed and equipped to

process fish on board the vessel.

Processing Plant Operations

0007In its simplest form, fin fish processing may involve

only simple evisceration. It may also be complex,

requiring specialized and expensive equipment, such

as in the value-added production of fish analogs.

Fin fish can be processed manually, with automated

equipment or, more typically, by using a combination.

Automated processing is more suited to processing

fish that are uniform in dimension and where high

volume is a consideration. Automated fish-processing

equipment can be expensive and may require a high

degree of maintenance. Manually processed fish, on

the other hand, generally provide the highest meat

yield, and this technique is used where product

appearance is a major consideration.

0008Although there can be many varied steps and tech-

niques used in fin fish processing, the common steps

that may be used include grading or sorting, heading,

evisceration, scaling, skinning, cutting, trimming,

filleting, and one of many methods of preservation. A

processing line is commonly used for fin fish oper-

ations. The raw material, usually whole, live, or

drawn fish, is introduced into the plant and moves

from one processing step to another until that day’s

delivery has been completed. Each processing step

must be synchronized to avoid bottlenecks and delays

in processing. Fish harvests can be seasonal or unpre-

dictable, and processing plants must cope with daily

shortages or gluts. The objective of fin fish-processing

operations is to maximize meat yield and product

FISH/Processing 2453

shelf-life, size and grade product accurately, and

generate the minimum amount of waste. Meat yield

is the bottom line and will depend upon the species

being processed and the method of processing used.

0009 Fish come in all sizes and shapes. Consequently, the

final product can vary greatly in size, shape, and

weight. There can be variability within the same

species. Markets, however, require product sizing uni-

formity and consistency. In the last few years, there

have been significant developments in sizing and

grading technology. Computers, using advanced

optic and weighing systems, can sort fish fillets and

other meat cuts quickly and accurately. Fin fish-

processing operations generate a significant amount

of waste in the form of viscera, skin, bones, and

unrecoverable meat. This is a growing problem since

disposal options are becoming more restrictive. Fish

processors are subject to governmental regulations,

as is any food manufacturer. Fish nomenclature,

fish-processing regulations, and international trade

requirements are all challenges to modern fin fish

processing. The following discussion considers some

of the significant preservation methods and value-

added products for processed fish.

Fresh Processing

0010 Fish products processed and offered as fresh have a

relatively short shelf-life. Depending on the quality of

the fish and the conditions of storage, the shelf-life

can be as short as a few days or as long as several

weeks. Typical fresh products include whole drawn,

headed, fillets, and other meat cuts. There is a direct

correlation between the temperature of fresh fish

products and the shelf-life. For maximum shelf-life,

fish should be stored at temperatures near the freezing

point of water (i.e., 0



C). At this point the flesh will

not freeze, but bacterial and enzymatic activities will

be minimized. As storage temperatures rise above



C, bacterial and enzymatic activities can increase

significantly, dramatically shortening the shelf-life.

Where applicable, crushed ice is used to hold fresh

fish. The ice maintains the desired temperature of the

fish. Water from the melting ice ‘washes’ microorgan-

isms from the product, thus extending shelf-life. Little

or no sophisticated packaging is required for the

product. Most fin fish can be processed for fresh

markets. (See Storage Stability: Parameters Affecting

Storage Stability.)

Frozen Processing

0011 To reach worldwide markets effectively, frozen fish

processing is becoming increasingly important. Not

all species of fish are suitable for freezing. Fish with a

high fat content may become rancid in a relatively

short time. In some cases, there may be undesirable

textural changes or discolorations. There are a variety

of frozen fish products, such as frozen fish blocks and

breaded products, that are not available using any

other method of preservation. Modern fish-freezing

technology and equipment are economical, efficient,

and specific for fish products. Bulk frozen products,

such as frozen fish blocks (fillets, mince, or other

meat cuts frozen as a single unit), are normally frozen

using a direct-contact freezer such as a plate freezer.

Individually quick frozen (IQF) products use the effi-

ciency and speed of cryogenic freezers. Other types of

freezers used in fish processing include blast and im-

mersion freezing (brine freezing). Regardless of the

type of freezing equipment used, there are common

factors that have an impact on the product quality.

(See Freezing: Blast and Plate Freezing; Cryogenic

Freezing.)

0012Rate of freezing Rapid freezing produces smaller ice

crystals than slow freezing. These smaller ice crystals

are responsible for less structural damage to the

fish flesh. In addition, rapid freezing minimizes the

destructive concentration of cellular constituents.

Rapid freezing is encouraged when processors use

thin, prechilled packages of fish, and high-capacity,

low-temperature freezers. (See Freezing: Principles.)

0013Freezer storage temperature There is no significant

microbiological activity in frozen fishery products,

but enzymatic activity can have a pronounced effect.

Most frozen fishery products must be maintained at

extremely low temperatures to negate enzyme de-

struction. Research shows that storage temperatures

in the range 23



to 29



C are acceptable for most

fishery products. Lower temperatures are even better

but, at some point, economic considerations are

prohibitive.

0014Packaging Frozen fish products are packaged to

minimize dehydration and oxidation. Desiccation of

poorly packaged frozen fish is a serious problem.

Over a period of time, a highly undesirable drying

condition (freezer burn) may occur. Fish fats and oils

are easily oxidized in the presence of air. The resulting

rancidity is responsible for undesirable flavors and

color. Fish processors depend on commercial pack-

aging materials and wraps to serve as effective bar-

riers to minimize dehydration and oxidation. The

fish-freezing industry has made great use of ice glazes

for minimizing these same effects, especially in IQF

products. Typically, ice glazes are formed by immers-

ing or spraying frozen fish fillets or other fish prod-

ucts in chilled water immediately after emerging from

the cryogenic freezing equipment. In this manner, a

2454 FISH/Processing

coating of ice is formed around the product. The fish-

processing industry also uses modified-atmospheric

packaging (MAP) and vacuum-packaging to extend

shelf-life and maintain quality. However, in the USA

the use of such technology may be restricted without

approved controls on fresh, unfrozen fish products

because of potential growth of anaerobic pathogens

such as Clostridium botulinum.(See Storage of

Frozen Foods; Freezing: Structural and Flavor (Fla-

vour) Changes.)

Fish Canning

0015 Fish has been successfully canned commercially for

more than 100 years. However, with the advent of

improvements in freezing technology, transportation,

marketing, and storage facilities, the percentage of

canned fish products has been declining. One of the

major advantages of canned fish is the relatively long

shelf-life when stored at ambient temperatures. At the

same time, canned fish is notably different from fresh

and frozen fish. Canning requires subjecting fish to

high temperatures to produce commercial sterility.

The resulting product is fully cooked. Salmon, tuna,

and herrings (including sardines and anchovies) are

species of high commercial value that are tradition-

ally canned. Fish may be delivered to the canning

facility fresh (salmon and herrings) or frozen (tuna).

Generally, fish are processed for canning by first

heading, eviscerating, scaling, and cleaning. Add-

itional processing steps can be quite variable,

depending on the species and the desired end product.

For example, salmon are packed raw into cans

and, although the fins are removed, the skin and

bones, which soften and are edible after processing,

are considered part of the pack. Tuna and some of

the herrings are cooked before packing the cans.

Cooking removes excess water from the fish tissue

and improves the appearance of the final pack.

Bones, skin, and dark-meat portions are removed

from tuna before packing into cans. (See Canning:

Principles.)

0016 Canned fish may or may not be packed with add-

itional ingredients, such as oils, water, or sauces.

Salmon are not generally packed with any additional

media. Tuna may be packed in vegetable oil, water, or

broth. Sardines and herrings may be packed in oils,

flavors, or a number of sauces such as mustard or

tomato. Cans used in the process are of many sizes

and shapes. Metal cans are sealed with double-

seaming machines that exhaust the head space to

produce the proper vacuum. Hermetic sealing is essen-

tial if product integrity is to be maintained throughout

heat processing, cooling, and storage. Leaks will

cause spoilage and jeopardize product safety. Canned

fish are low-acid foods and, consequently, will readily

support the growth of most microorganisms. Clostri-

dium botulinum is a heat-tolerant microorganism

capable of growing and producing a highly potent

toxin in canned fish that has been underprocessed,

or contaminated as a result of container leaks. For

this reason, most countries require minimum heat

process times and temperatures to destroy all micro-

biological vegetative cells and spores to commercial

sterility. Properly sealed and packed cans are heat-

processed using steam under pressure in a retort.

The processing time depends on can size, initial

temperature of the fish at the time of processing,

and the internal temperature of the retort. After pro-

cessing, cans are quickly cooled in cold chlorinated

water, labeled, and packed in shipping containers.

Canned fish are subject to deteriorative changes

during heat processing and subsequent storage.

For example, meat discoloration may occur if the

product is overprocessed. Struvite, a harmless glass-

like crystal of magnesium compounds, may develop

in canned tuna after an extended storage period; the

use of appropriate food additives, such as chelating

agents, usually minimizes the problem. (See Canning:

Quality Changes During Canning; Clostridium:

Occurrence of Clostridium botulinum; Botulism.)

Dried, Salted, or Smoked Fish Processing

0017Curing and drying fish with salt and smoke were

among the earliest methods used by humans to pre-

serve fish. Over the years, these products have de-

veloped traditional markets and today represent a

relatively small but important commercial segment

of the processed fish industry. These products depend

on low water activity to minimize the growth of

microorganisms. Dried salted fish are processed by

increasing tissue surface area, usually by splitting the

fish, packing in salt to reduce tissue moisture quickly

and, finally, air drying to achieve a moisture content

low enough to provide product stability. Smoked fish

can be processed using a variety of techniques and types

of equipment.There aretwo basic types of smokedfish:

cold-smoked and hot-smoked. Cold-smoked fish, as

the name implies, is generally processed at lower tem-

peratures than hot-smoked fish over a longer period of

time. The salt content may be higher and the texture

drier. Hot-smoked fish is succulent and is processed ina

significantly shorter period using much higher tem-

peratures. (See Preservation of Food; Smoked Foods:

Principles; Applications of Smoking.)

0018There are several important steps in the processing

of most smoked fish. Salting the raw fish before

smoking firms the texture, adds a desirable flavor

and, in some cases, may serve as a preservative.

Soaking fish in a brine solution is the most desirable

method of adding salt. This procedure provides

FISH/Processing 2455

control and uniformity. Several factors directly affect

the rate at which salt is absorbed, such as: (1) the

strength of the brine solution; (2) the amount of

exposed tissue (skin retards salts penetration); (3) the

fat content of the fish (the higher the fat content of the

fish, the slower the salt penetration); (4) the size of

the fish or pieces of fish (the larger the pieces, the

slower the penetration); and (5) the amount of agita-

tion and temperature of the brine. After brining, but

before smoking, the surface of the fish is air dried to

facilitate ‘pellicle’ formation.

0019 Drying is performed by a skilled individual and

usually within the oven that will be used to smoke

and cook the fish. A properly formed ‘pellicle’ will

produce an attractive finished product. Smoke par-

ticles will cling to its surface, imparting a pleasing

golden or bronze color. After drying, the fish is

smoked and then cooked to the required internal

temperature for a specified period. Cooking time

and temperature will vary, depending on the final

salt concentration and the use of other food additives.

Modern smoking ovens have automatic controls that

carefully monitor critical parameters. C. botulinum is

a microorganism of great concern to smoked fish

processors. In some countries, cooking times and

temperatures and salt concentrations are established

by regulations to eliminate the risk associated with

this organism. In addition, the final product must be

held under suitable refrigeration to prevent the

growth of microorganisms.

Further Processing

0020 Full use of the fish resource is a difficult challenge for

the processing industry. There are many species that,

because of economics and demand, are not suitable

for traditional processing. In addition, fish frames

and other filleting wastes resulting from processing

operations represent a significant source of recover-

able meat. Mechanical flesh-separating equipment

can be used to recover meat economically. Most

systems work by forcing edible meat through a per-

forated surface. In this way, the fish flesh is separated

from the skin, bones, and other unwanted fish waste

materials. The resulting comminuted material is

paste-like and is called fish mince. Ideally, the mince

should be as white in color as possible, but mince can

be dark if it contains blood, organs, or pigments.

Mince has many potential uses. Its primary use may

be as an extender in other fish and seafood products.

Fish mince may also serve as a base material for the

manufacture of analogs and other fabricated seafood

and meat products. Surimi is made from mince that

has been washed in water to remove many of the

solubles, including color, to render a highly functional

material. Surimi can be processed and formed into

various imitation seafood products, such as shrimp,

crabmeat, and lobster meat. The production of these

imitation seafood products from surimi is highly tech-

nical and requires expertise and sophisticated equip-

ment. The process begins with the addition of certain

functional ingredients that will give desired properties

to the final product, including water, starches, pro-

tein, fats, and other ingredients. In addition, various

natural and artificial colors and flavors may be

blended with the surimi to mimic the desired seafood

product. Ingredients including color and flavors used

must be in compliance with food regulations and

laws. The resulting product is extruded into the de-

sired shape, cooked, and packaged.

Quality Considerations

0021Fish and fish products are among the most perishable

of all foods. Decomposition and spoilage can begin

shortly after harvesting, and can be minimized only

with extreme care and diligence on the part of the

fisherman and processor. The two primary causes of

spoilage in fish are microbiological and enzymatic.

Bacteria are the primary microorganisms that affect

fish quality but molds and yeasts can also be respon-

sible for spoilage of fishery products. Large numbers

of microorganisms are found naturally in the gut and

body slime of living fish. When fish die as a result of

harvesting or when they are butchered during pro-

cessing, bacteria are introduced into muscle or organ

tissues and cause spoilage and decomposition. Under

favorable conditions, bacteria can grow and repro-

duce extremely rapidly. Unchecked, decomposition is

quick. Proper temperature controls and sanitation

procedures can provide the maximum shelf-life for

most seafood products. Fish may harbor a large var-

iety of bacteria, even some pathogens. However, since

fish are generally cooked prior to consumption, most

do not pose an immediate health hazard. Processing

techniques used to process fish require individual

evaluations to determine control methods. Please

refer to the previous example of C. botulinum and

the use of vacuum or MAP packaging.

0022Processors are concerned not only about the

number of microorganisms and controlling their

numbers, but also about contamination by specific

types of microorganisms. Pathogens, even in small

numbers, are capable of causing disease or producing

toxins. Naturally occurring proteolytic enzymes

cause spoilage, called autolysis, by producing undesir-

able textural and flavor changes. Like microbial

spoilage, the undesirable effects of enzymes are min-

imized by proper handling and temperature control.

However, unlike microbial spoilage, enzyme activity

may occur during frozen storage.

2456 FISH/Processing

0023 Several natural toxins may occur in processed fin

fish products. Ciguatera and scombroid (histamine)

are, perhaps, the most well known. Ciguatera is most

commonly associated with reef fish in tropical zones.

Fish flesh is made toxic as a result of fish consuming

the benthic dinoflagellate Gambierdiscus toxicus.

Scombroid poisoning is caused by the ingestion of

fish containing a high level of histamine. Histamine

is produced in fish flesh by enteric bacteria after

harvesting. In most cases, this condition can be traced

to improper cold storage of the fish. Scombridae

(tuna and mackerel) and Scomberesociadae fish

are more commonly associated with scombroid

poisoning, although other families have been impli-

cated. Other naturally occurring fish quality consider-

ations include paralytic shellfish poisoning and

parasites.

Fish Products

0024 Products resulting from fin fish processing are diverse

and complex and yet most of the world production

can be summarized within several categories

(Table 1). One reason for the complexity is product

and species nomenclature. The common name of a

fish or fish product in one region may not be the same

as in another. In addition, there is the large number of

fin fish species. A consistent and meaningful nomen-

clature system of fish and fish products is necessary

for international trade. Although there have been

attempts by various organizations and governmental

agencies to standardize fish nomenclature, this issue

remains a major problem not only in international

trade but also within commercial domestic trade.

Quality and sanitation are other major considerations

for fish products. Microorganism count and species

under certain conditions may give an indication of the

overall quality of the finished product and under

what conditions it was processed. These microbio-

logical requirements and standards, however, may

vary considerably among countries and nationalities.

In general, most countries involved in international

trade will consider aerobic plate count, enteric micro-

organisms, and pathogens as microbiological indica-

tors of food quality and sanitation. Mandatory

government fishery inspection programs are becom-

ing increasingly important. In the USA, the Hazard

Analysis Critical Control Point (HACCP) concept is

being considered as the basis for a national fishery

inspection program. HACCP requires processors to

evaluate all processing steps and to identify those

steps where hazards could occur if the step is not

controlled. Control systems, monitors and records

are required to insure that the processing of the fish

is in compliance with requirements. (See Hazard

Analysis Critical Control Point.)

See also: Canning: Principles; Quality Changes During

Canning; Clostridium: Occurrence of Clostridium

botulinum; Botulism; Freezing: Principles; Blast and Plate

Freezing; Cryogenic Freezing; Storage of Frozen Foods;

Structural and Flavor (Flavour) Changes; Hazard

Analysis Critical Control Point; Preservation of Food;

Smoked Foods: Principles; Applications of Smoking;

Storage Stability: Parameters Affecting Storage Stability