Total Lipids and Nutritionally Important Fatty Acids of Some Nova Scotia Fish and Shellfish Food Products

Can. Insl. Food 5ci. Technol. J. Vo!. 21, No. 4, pp. 390-398, 1988

RESEARCH

Total Lipids and Nutritionally Important Fatty Acids of Some Nova Scotia Fish and Shellfish Food Products R.G. Ackman and C. McLeod Canadian Institute of Fisheries Technology, Technical University of Nova Scotia Halifax, N.S., Canada B31 2X4

Abstract

of basic differences in fatty acid composition with lipid class (Ackman, 1980) there is usually more monoethylenic fatty acid and less polyunsaturated fatty acid in lipids of fish with high fat contents. The C20 and C n marine polyunsaturated fatty acids, often referred to as simply "omega-3" fatty acids, participate in complex body metabolic processes (Lands, 1986; Leaf and Weber, 1988) and are not included in most older data bases for fishery products. Shellfish have had a more chequered career in diet recommendations since the lipid is low and the total sterol is an important part of that lipid. Lately it has been recognized that at least half of this sterol is a mixture of phytosterols, with cholesterol approximating only half of the total (Gordon, 1982; Krzynowek, 1985). Human dietary studies with shellfish have in fact shown a beneficial effect of shellfish in the diet (Connor and Lin, 1982) but requests for numbers on cholesterol content are stilI frequently received. The production of seafood is a major industry in Nova Scotia, but the species and products are generally similar to those of Quebec, New Brunswick, Prince Edward Island, Newfoundland and New England. North-west Atlantic seafood is widely distributed in Canada and the U.S.A., but relevent new major data bases (Exler, 1987; Krzynowek and Murphy, 1987) on seafood composition, although well-written for general public information, often present too much information for the non-specialist. Recent popular publications (e.g., Nettleton, 1985), tend to reiterate older data. This report, although based on products available in Nova Scotia and generally produced in the region, has wider implications and should be useful to the lay public, dietitians and nutritionists, home economists and food scientists, and the fishing industry. The fishing industry of eastern Canada has a wide variety of commercially exploited fish and shellfish as its basic resource. The Halifax laboratory of the former Fisheries Research Board of Canada was a focus for lipid and fatty acid research into the composition and quality of many of these species. This

Public interest in the lipids of food product fish and shellfish has gone beyond a mere interest in cholesterol content and the total unsaturation of the fatty acids. It now includes specifically the content of eicosapentaenoic acid as well as other fatty acids of the linolenic or "omega-3" family. This report tabulates lipids, key fatty acids, and cholesterol contents for 72 products available in Nova Scotia and adjacent provinces. Several unfamiliar species are included since all available familiar fish and shellfish are now utilized and new resources must be tapped to supply the demand for fishery products, A limited number of canned and processed products are also included.

Resume L'interet du public dans les lipides presents dans les produits de poisson et de fruits de mer depasse un simple interet dans la teneur en cholesterol et dans le degre d'insaturation des acides gras, 11 inclut maintenant specifiquement la teneur en acide eicosapentaenoique ainsi que d'autres acides gras du groupe Iinolenique ou "omega-3". Ce rapport presente Ies teneurs en lipides, en acides gras clefs et en cholesterol pour 72 produits offerts en Nouvelle-Ecosse et dans les provinces adjacentes. Nous avons inclu plusieurs especes peu familieres puisque tous les poissons et fruits de mer familiers disponibles sont maintenant utilises et de nouvelles ressources doivent etre exploitees pour satisfaire a la demande pour des produits marins. Un nombre limite de produits en conserves et transformes sont egalement inclus.

Introduction The frequent recommendation that Canadians increase their fish consumption reflects the very rational view that fish fat is high in polyunsaturated fatty acids, yet that fish is generally low in total fat. The latter view is somewhat biased by the listed values for an important species, Atlantic cod (Gadus morhua), for which figures as low as 0.1010 or 0.3% lipid have been published (Sidwell, 1981). These figures reflect obsolete methods of fat determination and are misleading, since the basic minimal (cellular) lipid in cod muscle (fillet) is in the 0.6-0.7% range (Dambergs, 1959; BIigh and Scott, 1966; Addison et al., 1968; Hardy, 1980). Moreover, this basic composition extends to most fish (Ackman, 1980) and the additional fat above the basic cellular level of phospholipids is triglyceride (Exler et al., 1975). Because Copyright

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1988 Canadian Institute of Food Science and Technology

390

included information on both fatty acids and cholesterol which was either unpublished or published in journals not readily available to dietitians or other parties interested in fish and shellfish as food. T lis report pulls together the unpublished data, and the .:>lder information available in print, and is supplemented by recent analyses of a limited number of the fishery products currently available in the Nova Scotia region. It is not a comprehensive survey of the fishery resources of Canada. The variety of modified and convenience foods produced in Canada and based on fish and shellfish now available is increasing rapidly. It must be realized that, although Canada exported $1.6 billion worth of fishery products in 1983, it also imported $422 million worth of products in the same year (Anon, 1984). These imported products and ethnic preferences are added complications in dietary recommendations. This report can, however, basically help interpret the health benefits of such unfamiliar products if they are similar to Canadian products. In an increasing number of cases of low or reducedcalorie foods, the fish or shellfish content is minimal on a quantitative basis. To simplify the information for consumers, dietitians and researchers, we have therefore not included such products, although they are usually very acceptable and healthy alternatives to conventional meals based on red meats.

CHC1 3 and 200 mL MeOH for 2 min. The mixture was then blended with an aditional 100 mL of CHC1 3 for 30s and an additional 100 mL of water for 30s. The mixture was filtered on a Buchner funnel and the CHCl 3 layer was collected and washed with water. After drying over Na 2S04 and evaporating the solvent, the total lipid was weighed. A nitrogen atmosphere was maintained as much as possible. In preparation for GC analysis a portion of each lipid was methylated for 1 h with 70/0 BF3 MeOH. The recovered methyl esters were analyzed on a flexible fused silica column 30 m x 0.32 mm LD. coated with SUPELCOWAX-lO in a Perkin-Elmer Sigma 4 gas chromatograph equipped with a flame ionization detector. The column temperature was 172°C and the carrier gas pressure 8 psi. A hydrogenated sample was also analyzed to verify the quantitation of chain lengths. From the known amount of 22:0 standard originally added the total fatty acid content was calculated. Problems with interference of 22: 1 with 22:0 were overcome by re-injecting sample on a Durabondwax column in a Perkin-Elmer 3920 gas chromatograph equipped with a flame ionization detector and with a column temperature of 210°C and carrier gas pressure of 22 psi. The resulting separation of peaks allowed the calculation of the relative amounts of the two fatty acids.

Materials and Methods

Cholesterol Analysis

All fresh fish plus frozen swordfish analyzed in this study were purchased wholesale in Halifax, Nova Scotia. Cod, cusk, haddock, hake, winter flounder (sole), and wolffish were purchased as fresh fillets, weighing 500 g each. Halibut, salmon and swordfish were purchased as steaks and monkfish and trout as whole dressed fish. Canned products, crab products, and pickled herring were purchased commercialy from retail stores. Crab was purchased as shredded salad meat, frozen. Imitation crab legs (surimi) had been formed into sticks and frozen. The pickled herring was packed in a jar with onions and vinegar. Standard methyl behenate (22:0) and 5-a-cholestane were purchased from Serdary Research Laboratories (London, Ont.). All solvents were redistilled in glass under nitrogen.

For each sample, 50 mg of the total lipid collected was weighed into a 15 mL round bottom tube for cholesterol analysis using the method of Kovacs et al. (1979). A known amount of standard 5-a-cholestane was added, followed by 0.5 mL of 50% KOH and 2 mL of 95% ethanol. This mixture was heated to boiling in a water bath and stirred continuously for 1 h. At the end of this time the sample was extracted four times, each with 2 mL of hexane. The combined hexane extracts were concentrated by evaporation under nitrogen and the sample of unsaponifiables was injected into a 3.5 m fused silica column coated with methyl silicone in a Perkin-Elmer 900 series gas chromatograph equipped with a flame ionization detector. The column temperature was 280°C and the carrier gas pressure 30 psi.

Sample Preparation

Results

A 100 g sample of each fish was taken for analysis. Frozen foods were thawed before sampling. Canned herring and mackerel had the liquid drained from the can prior to sampling the solids. In the case of herring in tomato sauce, the fish was analyzed with whatever sauce remained on the flesh after draining. The pickled herring was removed from the liquid for sampling. Prior to analysis all fish samples were spiked with a known amount of standard methyl behenate made up in chloroform as an internal standard.

The lipids of edible parts of almost all groundfish and shellfish (Table I) can be taken as =:;2%. The exception on the Atlantic Coast is the Newfoundland turbot (formerly the Greenland halibut) Reinhardtius hippoglossoides (Ackman et al., 1967), and it has a parallel on the Pacific Coast in the sablefish Anoplopoma fimbria (Ackman, 1980). However, both of these fatty species of groundfish have fats of very low unsaturation, so their EPA and DHA content will be probably less than that of salmon, herring or mackerel with fat contents of 8-120/0. The pelagic/estuarial group is one of the most difficult to assess for fat content as these species usually have seasonal cycles of fat content associated with migration and spawning. The maximum fat con-

Lipid Extraction/GC Analysis Fish samples of 100 g were extracted for total lipid content by the method of Bligh and Dyer, 1959. The fish was blended in a Waring Blender with 100 mL Can. Inst. Food Sci. Technol. J. Vol. 21, No. 4, 1988

Ackman and McLeod / 391

Table I. Lipid Analysis: Amount of Total Lipid, Eicosapentaenoic (EPA) and Docosahexaenoic (DHA) Acids, Total n3 Acids, and Cholesterol, in Seafood Available from Nova Scotia Sources Total Lipid EPA (20:5n3) DHA (22:6n3) Total n3 Cholesterol (g/100g) (g/100g) (g/IOOg) (g/100g) (mg/100g) Groundfish Cod Cusk Haddock Hake (white) Halibut Monkfish Pollock (Bluefish) Redfish, Lean (Perch) Turbot Winter Flounder (Sole) Wolffish (Catfish)

0.73 0.67 0.59 0.69 2.04 0.42 1.10 1.15 10.0 0.45 0.59

0.08 0.03 0.07 0.05 0.16 0.03 0.08 0.14 0.34 0.Q7 0.11

0.23 0.09 0.14 0.22 0.22 0.07 0.18 0.Q7 0.28 0.12 0.06

0.32 0.13 0.23 0.30 0.45 0.11 0.26 0.21 0.84 0.22 0.20

Pelagic, Estuarial Argentine Capelin, Offshore Capelin, Inshore Eel, Frozen Gaspereau Herring Mackerel Mackerel, Smoked Salmon, Farm-Reared Smelt Sturgeon Swordfish, Frozen Trout, Farm-Reared

1.78 10.8 2.6 14.2 3.49 12.0 20.6 21.2 8.3 1.2 7.2 11.4 3.90

0.12 0.65 0.11 0.30 0.10 1.05 1.45 1.47 0.25 0.12 1.40 0.14 0.12

0.19 0.20 0.05 0.66 0.27 1.29 2.16 2.30 0.73 0.18 0.57 0.44 0.50

0.31 1.32 0.22 1.13 0.51 3.12 5.10 5.25 1.28 0.32 2.56 0.90 0.72

1.4 1.1 0.75 1.2 1.2 1.27 1.6 0.62 0.80 1.0 2.43 2.0

0.14 0.28 0.20 0.27 0.24 0.13 0.11 0.11 0.09 0.19 0.28 0.27

0.21 0.10 0.09 0.15 0.12 0.17 0.09 0.09 0.08 0.18 0.16 0.64

0.38 0.38 0.30 0.42 0.38 0.36 0.29 0.23 0.20 0.44 0.50 0.93

16.9 7.4

0.14 0.05

0.10

0.14 0.15

21.6 32.5

15.2 7.7 5.4

0.03 0.04 0.02

0.04 0.06 0.05

0.Q7 0.10 0.Q7

27.4 32.7 19.5

15.1 8.8

0.03 0.03

0.Q7

0.03 0.10

24.7 37.6

14.2

0.98

1.03

2.38

13.4 14.7

0.79 0.64

0.82 1.06

2.23 2.51

45.8 23.5

23.5 16.0

1.28 0.79

1.72 1.80

3.97 3.74

47.3 38.2

8.9 6.3 8.5 13.5

0.49 0.29 0.50 0.70

0.85 0.50 1.11 1.18

1.50 0.89 1.82 2.12

59.9 66.4 66.9 70.9

9.0 8.3

0.49 0.48

0.86 1.05

1.79 1.96

16.7

0.05

0.04

0.10

Molluscs, Crustaceans Clam (Surf) Crab (Jonah) Crab (Queen) Crab (Rock) Lobster Mussel Oyster (American) Quahog (Bay) Quahog (Ocean) Scallop Shrimp Squid Convenience Foods Boston Bluefish battered, frozen sticks, frozen Cod battered, frozen sticks, frozen cake, frozen Haddock battered, frozen sticks, frozen Herring pickled Herring (canned, drained solids) in tomato sauce smoked Mackerel (canned, drained solids) plain fillets smoked fillets Salmon (canned, drained solids) Pacific coho Pacific keta Pacific pink Pacific red sockeye Sardines, (canned, drained solids) in soya oil in water Sole battered, frozen

392 / Ackman and McLeod

34.6 31.8 29.3 22.9 19.8 16.7 50.2 15.1 32.1 22.8 151 42

34.7 73.2 43.7 44.9 65.6 78.4 76 70.9 69

26.7

J. Inst. Can. Sci. Technol. Alimenl. Vol. 21, No. 4, 1988

tent of edible parts is almost certainly 20070, and salmon, herring and mackerel usually have 6070 or more fat as a minimum, but can occasionally have less (Exler, 1987; Krzynowek and Murphy, 1987). Two capelin analyses are included to show that the proportions among omega-3 fatty acids are approximately proportional to lipid content although the proportion of triglycerides to phospholipids leads to some differences (Ackman, 1974; 1980; Exler et al., 1975). The fat contents of the convenience foods prepared from groundfish or shellfish are highly variable, depending on the type of pack. Nevertheless, if not diluted by too much vegetable components they are still useful sources of marine omega-3 fatty acids (Table 1).

The fatty acid details given in Table 2 omit the longchain monoethylenic fatty acids (20: 1 and 22: 1) which are not usually important in lean fish muscle, or in shellfish. In pelagic species they may occasionally be as much as half of the fat, but 25-35070 total would be more usual (Ackman, 1974; 1980). Increasing interest is apparent in the cardiovascular health benefits of monoethylenic fatty acids (Mattson and Grundy, 1985), but this has so far been restricted to the C l8 fatty acids. Broadly speaking, Table 2 shows that totals for saturated fatty acids and polyunsaturated fatty acids are approximately equal at about 25070 each of the fat with the balance made up of monoethylenic acids. When this fat is quantitatively important in the diet, it is reasonable to assume that

Table 2. Amount of 12 fatty acids in seafood available from Nova Scotia sources (g/100g). Groundfish Cod Cusk Haddock Hake (white) Halibut Monkfish Pollock (Bluefish) Redfish, Lean (Perch) Turbot Winter Flounder (Sole) Wolffish (Catfish) Pelagic, Estuarial Argentine Capelin, Offshore Capelin, Inshore Eel, Frozen Gaspereau Herring Mackerel Mackerel, Smoked Salmon, Farm-Reared Smelt Sturgeon Swordfish, Frozen Trout, Farm-Reared Can. Inst. Food Sci. Technol. J. Vol. 21, No. 4, 1988

14:0

16:0

16:1

18:0

18:1

18:2

18:3

18:4

20:4n6

20:5n3

22:5n3

22:6n3

.01 tr .01 .01 .06 .01 .01 .08 .61 .01 .01

.08 .03 .07 .08 .23 .04 .11 .20 1.09

.01 tr .01 .01 .17 .01 .02 .20 1.55 .02 .02

.02 .01 .02 .02 .07 .01 .03 .03 1.53 .02 .02

.05 .02 .05 .08 .54 .07 .09 .28 1.50 .03 .06

tra tr tr .01 .02 .01 tr .01 .10 tr

tr tr tr tr .01 tr tr tr .03 tr tr

tr tr tr tr .01 tr tr .01 .10 tr tr

.01 tr .02 .01 .03 .01 .01 tr .02 .02 .03

.08 .03 .07 .05 .16 .03 .08 .14 .34 .07 .11

.01 tr .01 .01 .04 tr tr .01 .06 .02 .02

.23 .09 .14 .22 .22 .07 .18 .07 .28 .12 .06

.12 1.43 .47

.05

.23 .97 .18 2.42 1.00 2.02 3.00 2.98 1.60 .25 1.39 1.85 .68

.10 .03 .05 .06 .22 .27 .25 .56 .01 .08 .06 .26

.10 .01 .04 .06 .22 .29 .32 .08 tr .05 .04 .03

.17 .04 tr .03 .39 .69 .66 .08 .01 .21 .05 .02

.03 tr .05

.12 .65 .11 .30 .10 1.05 1.45 1.47 .25 .12 1.40 .14 .12

.06 .01 .17 .04 .04 .13 .15 .11 .01 .20 .12 .03

.19 .20 .05 .66 .27 1.29 2.16 2.30 .73 .18 .57 .44 .50

.06 .05

.11 .33 .70 1.24 .19 .20 .26 1.55 .21 .56 .84 2.16 1.24 3.10 1.44 3.25 .21 .96 .04 .20 .26 l.l8 .20 .73 .13 .45

.72 .18 .80 1.06 U8 .49 .12 .49 .30 .28

.03 .27 .05 .14 .48 .48 .22 .03 .13 .38 .09

.02 .09 .10 .03 .02 .11 .03 .02

ReLb

I

2 3

4 5 6 I

7 8 8 9 10

Ackman and McLeod / 393

Table 2. (Cont'd) Molluscs, Crustaceans Clam (Surf) Crab (Jonah) Crab (Queen) Crab (Rock) Lobster Mussel Oyster (American) Quahog (Bay) Quahog (Ocean) Scallop Shrimp Squid Convenience Foods Boston Bluefish battered, frozen sticks, frozen Cod battered, frozen sticks, frozen cake, frozen Haddock battered, frozen sticks, frozen Herring pickled Herring (canned, drained solids) in tomato sauce smoked Mackerel (canned, drained solids) plain fillets smoked fillets Salmon (canned, drained solids) Pacific coho Pacific keta Pacific pink Pacific red sockeye Sardines, (canned, drained solids) in soya oil in water Sole battered, frozen Clams battered, frozen canned, drained solids Crab canned, drained solids frozen surimi Mussels canned, drained solids Oysters canned, drained solids smoked Scallops battered, frozen breaded, frozen Shrimp battered, frozen canned, drained solids atr - trace bReferences are: I) 2) 3) 4) 5) 6) 7) 8) 9) 10)

14:0

16:0

16:1

18:0

18:1

18:2

18:3

18:4

20:4n6

20:5n3

22:5n3

22:6n3

Ref. b

.02 .01 tr .01 .01 .04 .03 .01 .01 .DJ .05 .04

.18 .12 .09 .14 .18 .20 .28 .08 .01

.04 .04 .04 .04 .09 .10 .04

.Q7

.01

.04 .07

tr

.01

.03

.06

.27 .48

.26 .01

.01 .01 .03 .01 tr .01 .02 tr

tr .02 .02 .01 tr .04 .02 tr

.03 .03 .05 .02 .02 .10 .03 .02 .01

.15 .28 .20 .27 .24 .13 .11 .11 .09 .19 .28 .27

.03

.19 .14 .19 .29 .14 .08 .05 .05 .10 .37 .08

.01 .01 tr .01 .02 .01 .02 tr tr .01 .01 tr

.01

.17

.08 .05 .02 .05 .06 .05 .04 .03 .04 .04 .05 .08

.01 .01 tr .02 .tr

.21 .10 .09 .15 .12 .17 .09 .09 .08 .18 .16 .64

11 12 13 12 14 15 16 15 17 15 18 19

.03 .02

1.5 .87

.02 .03

.54 .25

3.71 2.16

3.93 1.90

.17 .08

tr tr

tr

.14 .05

tr

.10

.03

1.41 .66 .33

.03 .02 .01

.50 .23 .13

4.07 2.36 1.46

3.23 1.51 .73

.17

.02 .01

.08 .04

tr tr tr

tr tr tr

.03 .04 .02

tr tr tr

.04 .06 .05

.04 .07

1.71 2.39

.03 .03

.54 .29

4.37 2.24

4.48 .56

.23 tr

tr tr

tr

.03 .03

.49

5.27

.80

.08

.82

.09

.05

.17

.02

.98

.11

1.03

.54 .72

.83 1.12

.43 .40

.06 .08

.63 .79

.10 .15

.08 .17

.23 .44

.10 .02

.79 .64

.09 .08

.82 1.06

.60 .69

1.72 1.46

.87 .51

.33 .25

1.89 1.09

.19 .24

.15 .24

.34 .50

.04 .09

1.28 .79

.25 .15

1.72 1.80

.19 .23 .16 .37

.88 .53 .78 1.41

.41 .28 .22 .52

.23 .13 .21 .29

1.12 .89 1.03 2.08

.Q7

.04

.03 .08 .10

.09 .05 .17 .19

.06

.06 .13 .24

.03 .09 .11

.49 .29 .50 .70

.14 .10 .19 .22

.85 .50 1.11 1.18

.60 .58

1.05 1.07

.38 .47

.14 .10

.90 .69

.83 .10

.15 .14

.13 .20

.06 .03

.49 .48

.Q7

.06

.86 1.05

.04

1.98

.07

.65

5.45

5.39

.37

.01

tr

.05

.01

.04

.01

.03

1.03 .31

.02 .15

.48 .08

2.31 .13

4.80 .02

.53 tr

.02

tr tr

.02 .23

.04 tr

tr

tr .01 .01

.09 .05 .03

.04 .02 tr

.02 .01 .02

.14 .09 .02

tr tr

tr tr tr

tr tr tr

.02 .02 tr

.23 .17 .04

.02 .01 tr

.12 .12 .10

.04

.24

.01

.04

.07

.06

.06

.07

.03

.33

.02

.02

.14 .14

.54 2.19

.21 .12

.10 .26

.29 1.83

.06 5.51

.06 .07

.11 .07

.03 .01

.58 .28

.02 tr

.34 .27

.01 tr

.49 .39

.02 .01

.14 .18

1.33 1.64

1.12 .76

.06 .04

tr tr

tr tr

.03 .03

tr .03

.03 .04

.04 .02

1.42 .18

.05 .06

.48 .08

3.79 .18

3.22 .01

.19 tr

tr tr

tr

.01

.02 .20

tr tr

.01 .14

.03 .03

Kovacs, 1978, unpublished data; Ackman and Hooper, 1972, unpublished data; Ackman et al., 1967, Ackman and Harrington, 1975; Ratnayake, 1977; Ackman, 1980; Ackman et al., 1969; Ackman et al., 1975a; Bhuiyan et al., 1986a; Addison and Ackman, 1970; Ackman et al., 1975b;

394 / Ackman and McLeod

11) 12) 13) "14) 15) 16) 17) 18) 19)

.01 tr .02

.07

Krzynowek et al., 1983; Krzynowek et al., 1982; Addison et al., 1972; Castell , 1973, unpublished data; Paradis and Ackman, 1977, Ackman and Cormier, 1967; Watanabe and Ackman, 1974; Ackman et al., 1974; Ackman and Eaton, 1967; Jangaard and Ackman, 1965.

J. Inst. Can. Sci. Technol. Aliment. Vo!. 21, No. 4, 1988

marine food fats are similar to depot fat triglycerides which are the source of commercial fish oils for which additional analytical data is available (Ackman, 1980; 1982).

Discussion The organization of data for basic seafoods (Tables 1 and 2) follows that of the statistics on landings and values of Fisheries and Oceans Canada (Anon 1984; 1986a). For example on the Atlantic Coast total groundfish landings for 1985 were 765,000 tonnes, but this was dominated by cod at 478,000 tonnes. As a point of information for those unfamiliar with the industry it should be noted that Atlantic groundfish products (fresh or frozen) totalled 303,700 tonnes, of which only 176,800 tonnes were in filleted forms (i.e., with little further wastage in preparation for food use). The US market alone absorbed 137,167 tonnes of such groundfish products from both coasts, worth more than $478 million. Salted split fish took up a further 33,800 tonnes. The Atlantic pelagic group of fish landings of 258,680 tonnes was dominated by herring with landings of 188,800 tonnes of which smoked, pickled or canned products totalled 36,500 tonnes. In fact, probably half of the landings were roe herring. After removal of the roe (5,800 tonnes valued at $40 million) for export to Japan, some firms further process the rest of the bodies into frozen or cured products, or fish meal. However, a large quantity, perhaps as much as 50,000 tonnes of carcasses, is simply dumped at sea after removal of roe on shore (Anon, 1987a). In view of the above figures of wastage and exports it is not surprising that Canadian consumption of fish and shellfish is about 7 kg/capita/annum and that for 1985 this includes 136,130 tonnes of imports valued at $495,800,000. Yet if the often-quoted admonition to eat fish three times a week for good health were adopted, the population of Canada could easily be , supplied with 30-50,000 tonnes of product even if 10% were to switch from the extreme of no consumption of fish or shellfish to such a diet. The lipid content of groundfish flesh is quite low, usually ~ 1%. Landings of Atlantic halibut which is somewhat higher in fat, regrettably are low (3,800 tonnes in 1985) and the high fat Newfoundland turbot is not widely known in Canada, most being exported as frozen fillets. As a source of EPA and DHA it would not in fact be very good were it not for the high fat content. The commercial oil made from scrap is of exceptionally low iodine value (Ackman et al., 1967), reflecting the low EPA and DHA content and confirming this analysis. The pelagic fish are of the most interest for increasing the omega-3 fatty acids in the Canadian diet. Mackerel and capelin are underexploited resources, and Canadians eat much less herring than Europeans. Farmed Atlantic salmon is included in the landings and is a new and major growth industry. In 1987, harvesting should yield approximately 1,100 tonnes (D. Lemon, private communication). As long as these salmon are reared in seawater and are fed a high Can, Ins!, Faad Sd, Techno/, J, Vo/. 21, No, 4, 1988

proportion of fish scrap and/or fish oil then the fatty acids will be close in composition to those of wild salmon. West Scottish salmon, for example, had EPA of 0.89g/100g and DHA of 1.19g/100g. With 0.29g of 22:5n3, the total omega-3 acids were 2.55g/100g (Paul et al., 1978). This wild salmon had 11-12070 fat, or more than the farmed fish in the single analyses of Tables 1 and 2, hence the higher proportion of 22:6n3 in the latter from the quantitatively more important phospholipids (Exler et al., 1975; Ackman, 1980). Atlantic shellfish, in this context, does include both molluscs (scallops, oysters, clams, mussels) and crustaceans (lobster and shrimp), with landings of 145,240 tonnes. "Products", in 1985, totalled about half of this by weight, but the exports, primarily from the Atlantic Coast, were just over 50,000 tonnes. The culture of mussels has also expanded greatly in the last two years and will also now increase landings for shellfish. Mussels are mostly eaten as appetizers so their contribution of fatty acids to a meal is not necessarily a major one. The frequent inclusion of fish in lists of foods recommended for persons with high serum cholesterol (e.g., Walker, 1983) follows from wide acceptance of a correlation between serum cholesterol and risk of cardiovascular health problems (Anon, 1985a). Despite, or rather because this view is a "consensus" , various criticisms can be levelled at it (Mattson and Ahrens, 1985; Grundy, 1985; Jacoby and Rose, 1985; Olivier, 1985; Steinberg, 1985). Other more or less specific studies should also be considered (Harper, 1983; Flynn et al., 1985; Reiser et al., 1985). Despite recommendations that more fish be eaten, fish consumption has regrettably been virtually static for several decades in the U.S.A. (Welsh and Marston, 1982) and in Canada (Danielson and Robbins, 1984), and at about 7 kg/year/capita is notably well below the consumption by Japanese of 33-91 kg/year/capita (Hirai et al., 1980). In that country ischaemic heart death rates have been markedly lower than in western countries such as Sweden (Svanborg et al., 1985), an effect possibly related to the formerly very high consumption of fish in Japan (Shiba et al., 1980; Isibasi et al., 1987). Although fat content data is available (Anon, 1987b), there are no general guidelines on the fatty acid composition of food fat from Canadian marine animals as it is highly dependent on species and subject to seasonal variation (Ackman, 1974; 1982). The well-informed consumer presumably realizes that ~on­ venience foods or prepared products canned in oil, or breaded and deep fried, will have extra fat over and above the lipid native to the fish content. Others can still benefit from the EPA and DHA content of the fish/shellfish component since in effect the added cooking fat, usually of vegetable origin, is merely part of their normal high-fat diet. Thus, Singer et al. 1985 have shown that the EPA and/or DHA of mackerel is effective in reducing blood pressure in certain classes of patients when consumed as an addition to the customary East German diet. Among shellfish, most crab is an especially good Ackman and McLeod / 395

source of EPA (Table 2, see also Addison et al., 1972; Kryznowek et al., 1982; Kryznowek, 1985), but as is clear from Table 1, it should be emphasized that surimi crab does not contain as much in the way of useful dietary fatty acids. For bivalve shellfish, the decrease in the availability of waters free of domestic and industrial pollution is already a serious problem but some offshore resources, such as the ocean quahaug Arctica islandica, remain to be developed. Temporary health problems are not uncommon with all species of shellfish (Anon, 1986b). As sources of omega-3 fatty acids they can be grouped with the groundfish. The beneficial role of fish/shellfish lipids in cardiovascular health is not yet universally accepted. Dyerberg and Bang (1981) have postulated a definitive role for 20:5n3 (eicosapentaenoic acid or EPA). This C20 fatty acid, with five cis ethylenic bonds, is ubiquitous in lipids of marine fish and shellfish (Ackman, 1974; 1980), varying from 5 to 25% of total fatty acids. Usually it is accompanied by the C n fatty acid 22: 6n3 with six cis ethylenic bonds (docosahexaenoic acid or DHA). These two fatty acids are accompanied by both hexadecatetraenoic (16:4n3) and octadecatetraenoic (18:4n3) acids respectively at 2-5010 of the total, and collectively these have been dubbed the "omega-3" acids. This reflects a relationship to 18:3n3 (alpha-linolenic acid) from which the successors 18:4n3, 20:5n3 and 22:6n3 can be derived in animals (Lands, 1986). Linolenic acid itself seldom exceeds 1% of the fatty acids of marine animal lipids. While beneficial (Beare-Rogers, 1988), linolenic acid itself in the diet should not be assigned the presumed biochemical role of the marine EPA and DHA. The desired health benefits mayor may not be due solely to the EPA, and DHA looks increasingly effective as well (Leaf and Weber, 1988). The proportions of these two omega-3 fatty acids total at least 90% of all polyunsaturated fatty acids in North Atlantic and North Pacific species. The other major series of polyunsaturated fatty acids, called the omega-6 series, are chiefly represented in marine lipids by the parent 18:2n6 (linoleic acid) and its successor 20:4n6 (arachidonic acid). The two seldom total more than 2% of total fatty acids. These polyunsaturated fatty acids are complemented by palmitic acid (16:0) with rather less myristic acid (14:0), and relatively little stearic acid (18:0). While the two shorter-chain monoethylenic fatty acids 16: 1 and 18: 1 are ubiquitous, the relative proportions in fish lipids of 20: 1 and 22: 1 are variable since these are of exogenous origin (Ackman et al., 1980). In Japan, with a low cardiovascular health risk and a traditional fish-oriented diet, the intake of EPA has been estimated to be up to 0.5 g/day (Hirai et al., 1980; Kagawa et al., 1982), or more (Terano et al., 1983), whereas in European (British) diets the 19th century (1840) estimated intake of 1.7 g/week has dropped to 0.2 g/week in the late 20th century (Rice, 1984). A similar figure calculated for Britain is 0.1 g/person/day (Bull et al., 1983), and this "average" probably exceeds the intake in North America generally. 396 / Ackman and McLeod

The study of Kromhout et al. (1985) provided enough food information to allow an estimation of EPA intake of 140 mg/day in the dietary group eating fish regularly. This finding, based on a twenty-year study of adult males in Zutphen, the Netherlands, created a sensation in the media and has greatly stimulated public interest in increasing the fish and shellfish content in their diet. In brief, adult males consuming fish two or three times per week, to give a daily intake of 30 g/day, had a reduction by half in coronary heart disease mortality. An independent Swedish study, over fourteen years, has confirmed this type of relationship (Norell et al., 1986). The wider dietary health interactions and social implications of increasing consumption of marine fatty acids are very complex (Lands, 1986), and based in part on epidemiological considerations (Dyerberg and Bang, 1979; Bang et al., 1980; Bang and Dyerberg, 1980; Bang and Dyerberg, 1981; Kagawa et al., 1982). There are over 200 scientific papers on the subject recorded, but public interest has forced both the food industry (Kinsella, 1986) and the fishing industry (Anon, 1985c; McKnight et al., 1985; Anon, 1986c) to examine the marketing aspects of EPA very intensively. A serious question is that of supplies of food fish and shellfish. Familiar species of food fish are already exploited to the limit of availability, and aquaculture is not apt to provide low-cost supplemental products in the volume thought necessary by increased public interest. Unfamiliar species such as cusk (Brosme brosme) and the wolffish (Anarhichas lupus), newly renamed the ocean catfish, an irrational step since it is now designated as non-kosher, are alternatives for which we have included data. Fatty fish, notably herring (Clupea harengus) and mackerel (Scomber scombrus) are potential low-cost valuable sources of dietary EPA, and contain relatively little cholesterol. The two are not necessarily comparable as dietary sources of EPA (cL Singer et al., 1985) and are possibly less than attractive as a steady diet, but would provide tasty additions and variety to a basic diet high in fish and shellfish. Quality problems with mackerel have been partly overcome (Ke et al., 1976). Smoked mackerel, for example, retains almost all polyunsaturated fatty acids, including EPA (Bhuiyan et al., 1986a) in a form slightly enriched by water removal (Bhuiyan et al., 1986b). Pacific salmon, canned or as fillets, are good sources, as are farmed Atlantic salmon. Canned products, such as herring fillets and Canadian sardines, are also very good sources of EPA, but tuna is possibly less valuable in that context as several species are quite lean and DHA markedly exceeds EPA (Exler et al., 1975). In some respects the basic biochemical roles of the omega-3 and omega-6 fatty acids in human nutrition are well understood (Goodnight et al., 1982). Much research is however still needed and in December of 1985 the National Institute of Health of the U.S.A. called for research proposals on omega-3 fatty acids (Anon, 1985b). This interest of a major U.S. agency funding health research emphasizes the serious attitude that many responsible parties take in regard to the J. Inst. Can. Sci. Technol. Aliment. Vo!. 21, No. 4, 1988

potential health benefits of the polyunsaturated fatty acids of seafoods.

Acknowledgements Some of the data compiled in this report was accumulated prior to 1979 during the operations of the Halifax Laboratory, Fisheries Research Board of Canada. M.LP. Kovacs, S.N. Hooper, C.A. Eaton and others contributed to these records. The Province of Nova Scotia supported parts of the investigation under the Canada-Nova Scotia Fisheries Development Subagreement.

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J. Inst. Can. Sei. Teehnol. Aliment. Vo!. 21, No. 4, 1988