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Lipids and fatty acids in muscle, liver and skin of three edible fish from the Senegalese coast: Sardinella maderensis, Sardinella aurita and Cephalopholis taeniops
Comparative Biochemistry and Physiology Part B 131 (2002) 395–402
Lipids and fatty acids in muscle, liver and skin of three edible fish from the Senegalese coast: Sardinella maderensis, Sardinella aurita and Cephalopholis taeniops Jean-Michel Njinkoue´ a, Gilles Barnathanb,*, Joseph Mirallesc, Emile-Marcel Gaydoud, Abdoulaye Sambe a
´ Departement de Biochimie, Faculte´ des Sciences, Universite´ de Douala, Douala, Cameroun Laboratoire de Chimie Marine, ISOMer, SMAB, UPRES-EA 2160, Universite´ de Nantes, 2, rue de La Houssiniere, BP 92208, F-44322 Nantes Cedex 3, France c ´ Departement de Biologie, Faculte´ des Sciences, Nouakchott, Mauritanie d Laboratoire de Phytochimie, Faculte´ des Sciences, Universite´ Aix-Marseille III, Marseille, France e ´ Laboratoire des Produits Naturels, Departement de Chimie, Faculte´ des Sciences et Techniques, Universite´ Cheikh Anta Diop, ´ ´ Dakar, Senegal b
Received 27 July 2001; received in revised form 12 November 2001; accepted 22 November 2001
Abstract Lipid content and fatty acid composition were determined in three species of edible fish caught in Senegalese waters during the upwelling season (January, 1993). Sardinella maderensis and Sardinella aurita are fat fish containing more than 5% (fresh wt.) of lipids, whereas Cephalopholis taeniops is a lean fish with approximately 1% of lipids. Skin, liver and muscle were studied for each fish species. About 40 fatty acids were identified by GC and GCyMS as methyl esters and N-acyl pyrrolidides. Palmitic acid was the main acid in the muscle and skin of all samples studied (20–33% of total fatty acids). Oleic acid was the main fatty acid in the liver of S. maderensis (27.2%"0.1) and S. aurita (44.7%"0.1). Arachidonic acid was a minor component in all samples. The flesh (muscle) of the three fish species contained high concentrations of v3 polyunsaturated fatty acids (PUFA), ranging from 16.0 to 29.1% and including 20:5 v3 (eicosapentaenoic acid, EPA) and 22:6 v3 (docosahexaenoic acid, DHA) acids as major components. These two acids together accounted for 24.7%"0.1 and 12.9%"0.1 of total acids in the skin of S. maderensis and S. aurita, respectively. The percentages of PUFA found in the fish studied were very similar to those in fish used commercially as sources of PUFA. Muscle sterols, which accounted for 9–11% of total lipids, consisted mainly of cholesterol (up to 97% of total sterols). 䊚 2002 Elsevier Science Inc. All rights reserved. Keywords: Lipid content; Fatty acid composition; Senegalese fish; Sardinella maderensis; Sardinella aurita; Cephalopholis taeniops; Polyunsaturated fatty acids
1. Introduction Fish is a major source of food for mankind, Abbreviations: CC: column chromatography; DHA: docosahexaenoic acid; EPA: eicosapentaenoic acid; GCyMS: Gas chromatographyymass spectrometry; PUFA: polyunsaturated fatty acid; TLC: thin-layer chromatography. *Corresponding author. Tel.: q33-25112-5689; fax: q3324041-2858. E-mail address: [email protected] (G. Barnathan).
providing a significant amount of the animal protein diet in many countries. As compared to red meat, fish flesh is easily digestible because it contains long muscle fibres. Moreover, the consumption of fish has been linked to health benefits, such as reduced risk of coronary heart disease, which are largely attributable to the polyunsaturated fatty acids (PUFA) in fish oils (Morris and Culkin, 1989; Burr, 1992; Paige et al., 1996). A preventive andyor curative effect has also been
1096-4959/02/$ - see front matter 䊚 2002 Elsevier Science Inc. All rights reserved. PII: S 1 0 9 6 - 4 9 5 9 Ž 0 1 . 0 0 5 0 6 - 1
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reported for arterial hypertension (Millar and Waal-Manning, 1992), human breast cancer growth (Rose and Connoll, 1993), inflammatory diseases (Belluzi et al., 1993; James and Cleland, 1996), asthma (Dry and Vincent, 1991; Hodge et al., 1996), and disorders of the immune system (Levine and Labuza, 1990; Kenneth, 1986). These beneficial PUFA can be divided into two biochemical families, v3 and v6, with different biological effects (James and Cleland, 1996). The coast of Senegal and Mauritania, with its vast continental shelf and alternating cold and warm marine currents, is the richest area of West Africa for seafood resources (mainly fish). No detailed chemical studies of the lipid and fatty acid content of these fish are available, even though Sardinella maderensis and S. aurita, two small pelagic fish, constitute a large portion of catches and are the species most often consumed in Senegal. The present study compared these two fat fish (at least 5% of lipidsyfresh wt.) with a lean fish, Cephalopholis taeniops (approximately 1% of lipids), exploited mainly for exportation. There is increasing interest today in fish and fish oils because of their PUFA content. Fish liver has long been a source of oils, (e.g. cod liver oil) for the prevention of vision and growth problems. Liver and skin are often discarded when fish are prepared for consumption, but they were included in this study, together with muscle, to determine their possible nutritional and therapeutic value. As lipid content shows seasonal variations, it seemed appropriate to choose a study period in which fish accumulate the most lipids, i.e. during upwelling when waters highly rich in nutrients and salts rise from the ocean depths to the surface. This study compared the lipid and fatty acid composition of the skin, liver and flesh (white or smooth muscle and red or striped muscle) of the three fish species. 2. Materials and methods The three marine fish species studied, Sardinella maderensis, S. aurita, and Cephalopholis taeniops, are staples of the native fishing industry. The specimens used were purchased fresh at local fish markets in Dakar (Senegal), in January, 1993 during the upwelling period and from July to October during the warm season. Specimens were transported on ice to the laboratory where they were weighed and immediately processed. The specimens were dissected and the organs to be
studied were removed. Water content was determined by drying muscle samples. The organs were extracted separately for total lipids by homogenisation in a Waring blender for 2 min with a mixture of CH2Cl2 yMeOH (1:1, vyv). The crude extract was split into two parts. The first was chromatographed on an open silica gel column to obtain the different lipid classes by the usual methods (Pham Quang and Laur, 1974; Araki et al., 1986). Phospholipid composition was analysed by thin-layer chromatography (TLC) using chloroformymethanolywater (65:25:4, vyv) as eluent. Silica gel 60-W plates (Merck) with a size of 20=20 cm and a layer thickness of 0.25 mm were used. Glycolipid composition was analysed by TLC according to Araki et al. (1986). Silica gel (70–230 mesh) column chromatography (CC) was performed with hexane, chloroform (neutral lipids), acetone (glycolipids) and methanol (phospholipids) as successive eluents. Glycolipid and phospholipid classes were quantified by preparative TLC. The second part of the crude extract was saponified (KOHyEtOH, 2 M), for 2 h under reflux. The fatty acids obtained were converted into methyl esters by reaction (30 min under reflux) with methanolic hydrogen chloride, dissolved in hexane (Carreau and Dubacq, 1978) and purified by silica gel CC with hexaneydiethyl ether (10:1, vyv) as eluent or by thin-layer chromatography (TLC) with the same eluent. The resulting methyl esters were firstly analysed by gas chromatography (GC) using a Carlo-Erba 4130 chromatograph, a non-polar OV-1 silica capillary column (25 m=0.32 mm i.d., 0.4-mm film thickness) or a polar Carbowax 20 M silica capillary column (50 m=0.32 mm i.d., 0.4-mm film thickness). The carrier gas was hydrogen (0.6 bars, split 5y100). Column temperature was programmed from 190 8C to 230 8C at 2 8Cymin. Nacyl pyrrolidides were prepared by direct treatment of methyl esters with pyrrolidineyacetic acid (10:1, vyv) for 2 h under reflux and purified by TLC on 0.5-mm silica gel layers, using hexaney diethyl ether (1:2, vyv) as developing solvent. GCyMS analyses of methyl esters and N-acyl pyrrolidides were performed on a Hewlett-Packard HP-5890 (GC) and 5989A instrument (MS) linked to an HP 9000y345 integrator. The GC column was a 30 m=0.32 mm i.d. fused silica capillary column coated with non-polar DB-1 (0.25-mm film thickness). The carrier gas was helium. Column
J.-M. Njinkoue´ et al. / Comparative Biochemistry and Physiology Part B 131 (2002) 395–402
397
Table 1 Total lipid content (% of fresh wt.) in the organsa of studied fish Fish
Skin
Liver
White muscle
Red muscle
S. maderensis S. aurita C. taeniops
26.0 (0.6) 24.0 (0.8) 2.4 (0.3)
10.0 (0.9) 12.0 (0.9) 8.0 (0.6)
5.0 (0.7) 3.5 (0.4) 1.3 (0.2)
21.0 (0.9) 10.0 (0.9) –b
ns10. S.D. in brackets. a White muscle is the major organ component, followed by red muscle, skin and liver. b C. taeniops is devoid of red muscle.
temperature was programmed from 180 to 300 8C at 3 8Cymin in order to get the better resolution. The detector and injector temperature was 250 8C. Total sterols were extracted from unsaponifiable fraction by silica gel column using chloroform as eluent and analysed as acetates by GC under the following conditions: OV-1 column as described above, hydrogen as carrier gas, and a column temperature of 230 8C. The detector and injector temperature was 250 8C. Data statistical analysis was carried out with a Sigmastat software (version 2.03). Data were subjected to Student’s t-test for determining significant differences between means. Each sample lot consisted of six fish. Data are expressed as mean"S.D., n values are given for each Table. 3. Results Table 1 shows the lipid content of different parts (skin, liver, muscle) of the three edible fish species studied during the same upwelling period. Lipid content ranged from 1.3%"0.2 (white muscle of C. taeniops) to 26.0%"0.6 (skin of S. maderensis). As shown in Table 1, S. maderensis contained more lipids than S. aurita, especially in red muscle (twice as much). Red muscle of the Sardinella species contained more lipids than white muscle: approximately 3 times as much in S. aurita and 4 times as much in S. maderensis. Both Sardinella species had similar lipid content in skin. Lipid content in liver was also similar in the Sardinella
species. C. taeniops, which is devoid of striped muscle, had much lower lipid content than the two Sardinella species. The lipids of C. taeniops were concentrated particularly in liver, which contained more than muscle and skin. The liver of the three fish species contained 8.0%"0.6 to 12.0%"0.9 of total lipids and represented 1.1%"0.2 to 2.0%"0.5 of total body weight: 1.1%"0.2 of body weight and 8.0%"0.6 of lipids for C. taeniops; 2.0%"0.5 and 12.0%"0.9, respectively for S. aurita; and 1.5%"0.2 and 10.0%"0.9, respectively for S. maderensis. The following values were obtained from the Student’s t-test for each organ from both Sardinella species: for skin, ts 6.382, d.f. (degree of freedom)s18, P-0.001; for liver, ts4.940, d.f. s18, P-0.001; for white muscle, ts5.590, d.f.s18, P-0.001; and for red muscle, ts28.194, d.f.s18, P-0.001. A significant difference (P-0.001) was found between the lipid contents in Sardinella. Therefore, a significant difference was also found between Sardinella and C. taeniops. Lipid content differed according to season. In the warm season, when waters were poor in nutrients and mineral salts, the value ranged from 2.8"0.2 to 4.0%"0.2 in white muscle of the two Sardinella species and was F0.8%"0.2 in C. taeniops muscle. Lipid content differed not only from one organ to another, but also inversely to water content. For example, the water content for C. taeniops was 68.8%"0.4 in liver, 73.3%"0.5
Table 2 Water content (%) of the fish muscles and liver C. taeniops
S. maderensis
Muscle 80.0"0.8
White muscle 72.0"0.7
Liver 68.8"0.4
71.2"0.5
ns10.
S. aurita Red muscle 65.0"0.6
White muscle 73.0"0.6 73.7"0.6
Red muscle 68.0"0.9
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J.-M. Njinkoue´ et al. / Comparative Biochemistry and Physiology Part B 131 (2002) 395–402
Table 3 Sterol content and composition of white muscle in the three fish species Fish species
Sterol contenta
Cholesterolb
Campesterolb
S. maderensis S. aurita C. taeniops
9.8"0.5 9.5"0.4 10.8"0.5
97.0"0.8 98.0"0.4 99.3"0.3
3.0"0.2 2.0"0.2 0.3"0.1
ns5. a As a percentage of total lipids. b As a percentage of total sterols.
in skin and 80.0%"0.8 in muscle. Table 2 shows the water content in the muscles and in the liver of both Sardinella and C. taeniops. The Student’s t-test showed a significant difference between water contents in fish muscles: ts3.388, d.f.s18, Ps0.003 for the white muscle; and ts8.321, d.f.s18, P-0.001 for the red muscle. The average total lipid fraction in white muscle contained 10.0"0.4 to 15.0"0.5% polar lipids. The major phospholipid classes were shown to be phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol, and the major glycolipid classes were shown to be monogalactosyldiglyceride and digalactosyldiglyceride, as judged by TLC analysis in the three fish. Phospholipids accounted for 10.0"0.1% and 6.0"0.2% of total white muscle lipids in C. taeniops and both Sardinella species, respectively. It was observed that phospholipid content tended to be higher in fish with low lipid content. Unsaponifiable matter represented 17–19% of the fish total lipids. Sterols accounted for approximately 56% of the unsaponifiable matter in the three fish. As shown in Table 3, the sterol content in lipids of white muscle (the major site) was 9.8%"0.5 of total lipid weight in S. maderensis, 9.5%"0.4 in S. aurita and 10.8%"0.5 in C. taeniops. Two sterols were only present in all cases, namely campesterol and cholesterol as the major sterol (97–99%). Fatty acids represented 60.0–70.0% of total lipid weight in the three fish species. Approximately 40 fatty acids were characterised as methyl esters and N-acyl pyrrolidides by GC and GCyMS. Table 4 shows the fatty acid profiles of the three fish species, which are listed in the order of chromatographic retention time and the number of their carbons and unsaturations. The main acid in all samples analysed was palmitic acid (20.0–33.0% of total fatty acids), except in the liver of S.
maderensis and S. aurita where oleic acid was the main acid, accounting for 26.0% and 44.0% of fatty acids, respectively. Arachidonic acid was a minor compound in all fatty acid mixtures analysed. Saturated fatty acids accounted for 32.0– 58.0% in the different fatty acid mixtures. These species of fish are poor in branched fatty acids and no isoprenoid fatty acid was detected. An interesting result of this study was the content found for v3 PUFA, which ranged from 16.0 to 32.0%. The 20:5 v3 (EPA) and 22:6 v3 (DHA) acids were major components of the series in flesh and skin of the three fish species. The flesh and skin of all three species contained a similar percentage of saturated fatty acids, whereas the liver of C. taeniops contained more saturated fatty acids than those of the two Sardinella species. All specimens showed low amounts of v6 PUFA. 4. Discussion The two Sardinella species are closely related, have a similar diet and occupy the same geographical areas. The growth and reproductive patterns of both species, as well as their exploitation as food resources, are highly influenced by the dynamics of upwelling systems (Cury and Fontana, 1988). These common edible fish were caught in Senegalese waters in January, 1993 during the upwelling period. Along the coasts of Senegal and Mauritania, S. maderensis is richer in lipids than S. aurita, whereas along the Congolese coasts the curve for monthly variations in the fatty acid content of S. aurita remains above that of S. maderensis throughout the year (Cury and Fontana, 1988). In the warm season (July to October), when waters are poor in nutrients and mineral salts, lipid content decreases considerably, dropping to 2.8%, and G0.8% in the muscle of S. aurita and C. taeniops, respectively. In fat fish, the lipid content of both types of muscle is richer in older animals. The considerable variation in lipid content reported in many studies on fish in different areas around the world is apparently due to factors such as season, temperature, diet, age, size and sex (Kherunnisa et al., 1996). Compared to the oil content of muscle, the liver of C. taeniops contains significant lipid content. However, this liver content is low compared to that of other lean fish, such as the cod and certain shark species in which the liver represents, respec-
Table 4 Fatty acid composition (% total fatty acids) of total lipids from three Senegalese fish species: Sardinella maderensis (A), S. aurita (B) and Cephalopholis taeniops (C)a Fatty acids
White muscle
Red muscle
Liver
Skin
C
A
B
C
A
B
C
A
B
C
7.8"0.2 0.5"0.1 0.7"0.1 23.2"0.5 Tr 1.8"0.1 6.2"0.2 0.6"0.1 2.5"0.3 0.3"0.1 43.6"0.5
4.0"0.1 0.3"0.1 0.4"0.1 31.4"0.1 Tr 1.2"0.1 10.5"0.4 0.5"0.1 0.3"0.1 0.8"0.1 49.4"0.2
8.3"0.1 Tr 0.6"0.1 25.6"0.1 Tr 1.8"0.1 6.4"0.1 0.9"0.1 3.1"0.1 0.8"0.1 47.5"0.5
5.9"0.1 0.3"0.1 0.6"0.1 23.1"0.1 Tr 1.4"0.1 6.4"0.1 0.8"0.1 1.8"0.1 0.3"0.1 40.6"0.5
– – – – – – – – – – –
3.2"0.1 0.3"0.1 0.3"0.1 25.6"0.1 0.3"0.1 1.1"0.1 5.4"0.1 0.3"0.1 0.5"0.1 1.0"0.1 38.0"0.3
2.0"0.1 – 0.3"0.1 23.2"0.2 Tr 0.3"0.1 5.0"0.1 0.3"0.1 0.9"0.2 0.3"0.1 32.3"0.5
9.2"0.1 1.7"0.1 2.4"0.1 33.9"0.1 Tr 1.4"0.1 9.2"0.1 0.3"0.1 0.5"0.1 Tr 58.6"0.3
8.1"0.1 0.3"0.1 0.5"0.1 20.5"0.2 0.3"0.1 2.0"0.1 5.8"0.1 1.2"0.1 2.3"0.1 0.5"0.1 41.5"0.4
7.8"0.1 0.4"0.1 0.6"0.1 20.5"0.1 Tr 1.8"0.1 5.6"0.1 0.8"0.1 2.5"0.1 0.3"0.1 40.3"0.2
5.0"0.1 0.3"0.1 0.7"0.1 28.4"0.2 0.4"0.1 1.0"0.1 8.4"0.1 0.3"0.1 0.3"0.1 1.6"0.1 46.4"0.4
Monounsaturated fatty acids (MUFA) % 16:1 v8 0.4"0.1 0.7"0.2 18:1 v7 9.2"0.2 9.5"0.1 7-Me-16:1v10 Tr 0.7"0.1 17:1 v9 1.1"0.1 1.0"0.1 18:1 v9 7.7"0.2 14.4"0.2 18:1 v7 4.4"0.1 5.1"0.5 20:1 v12 0.3"0.1 0.3"0.1 20:1 v9 1.9"0.1 1.4"0.4 20:1 v7 0.4"0.1 Tr 22:1 v11 Tr 0.3"0.2 24:1 v9 0.8"0.1 1.0"0.2 S MUFA 26.5"0.5 34.4"0.9
0.5"0.1 9.5"0.1 – 0.6"0.1 11.6"0.1 5.3"0.2 0.3"0.1 1.2"0.1 0.3"0.1 0.3"0.1 1.0"0.1 30.6"0.4
0.6"0.1 8.1"0.1 0.6"0.1 0.8"0.1 10.4"0.1 4.9"0.1 0.4"0.1 2.8"0.1 0.4"0.1 0.4"0.1 0.5"0.1 29.9"0.5
– 6.1"0.1 0.3"0.1 0.8"0.1 13.7"0.1 4.0"0.1 0.3"0.1 1.4"0.1 Tr Tr Tr 26.6"0.4
– – – – – – – – – – – –
0.7"0.1 3.9"0.1 0.5"0.1 0.3"0.1 27.2"0.1 6.6"0.1 0.4"0.1 3.2"0.1 0.5"0.1 0.6"0.1 0.3"0.1 44.2"0.6
0.6"0.1 2.6"0.1 Tr Tr 44.7"0.2 4.0"0.1 0.4"0.1 1.7"0.1 Tr Tr Tr 54.0"0.1
0.8"0.1 16.4"0.1 – 0.5"0.1 8.6"0.1 3.4"0.1 1.0"0.1 – Tr – – 30.7"0.2
– 8.0"0.1 0.3"0.1 1.4"0.1 8.2"0.1 3.1"0.1 1.9"0.1 – 0.3"0.1 Tr Tr 23.2"0.3
0.4"0.1 10.1"0.1 Tr 1.2"0.1 15.5"0.1 4.2"0.1 0.3"0.1 1.6"0.2 0.3"0.1 0.4"0.1 Tr 34.0"0.3
1.2"0.1 11.8"0.1 Tr 0.3"0.1 12.5"0.1 4.3"0.2 Tr 1.5"0.1 0.3"0.2 1.7"0.1 Tr 33.6"0.4
Diunsaturated fatty acids ( DUFA ) % 18:2 v6 0.3"0.2 0.7"0.2 18:2 0.9"0.1 0.6"0.1 20:2 v9 0.7"0.1 1.1"0.2 S DUFA 1.9" 2.4"0.2
0.7"0.1 – Tr 0.7"0.1
1.0"0.1 0.5"0.1 Tr 1.5"0.1
0.6"0.1 0.4"0.1 0.9"0.1 1.9"0.1
– – – –
0.5"0.1 0.5"0.1 0.7"0.1 1.7"0.3
1.7"0.1 0.3"0.1 4.3"0.1 6.3"0.2
0.5"0.1 Tr 0.3"0.1 0.8"0.2
1.2"0.1 0.7"0.1 0.3"0.1 2.2"0.1
0.7"0.1 0.8"0.1 1.2"0.1 2.7"0.2
0.8 0.3 Tr 1.1
Triunsaturated fatty acids ( TrUFA ) % 16:3 v4 0.3"0.2 0.4"0.2 18:3 v6 0.4"0.1 0.5"0.3 18:3 Tr Tr 18:3 v3 0.3"0.1 0.3"0.2 20:3 v3 1.1"0.2 0.7"0.2 S TrUFA 2.1"0.3 1.9"0.5
Tr 0.3"0.2 0.3"0.1 Tr 0.7"0.1 1.3"0.2
0.3"0.1 Tr 0.3"0.1 0.5"0.1 1.0"0.1 2.1"0.2
Tr 0.4"0.1 Tr 0.4"0.1 0.9"02 1.7"0.1
– – – – – –
0.4"0.1 0.3"0.1 0.4"0.1 0.4"0.1 0.5"0.1 2.0"0.3
0.5"0.1 0.3"0.1 Tr 0.7"0.1 0.3"0.1 1.8"0.4
0.8"0.1 Tr – 0.9"0.1 1"0.1 2.7"0.2
Tr 0.3"0.1 0.8"0.1 0.3"0.1 0.3"0.1 1.7"0.2
0.3"0.1 0.8"0.1 0.3"0.1 0.3"0.1 0.6"0.1 2.3"0.2
Tr 0.3"0.1 0.3"0.1 0.3"0.1 1.7"0.1 2.6"0.3
Saturated fatty acids ( SFA) % 14:0 11.0"0.6 Iso-15:0 0.6"0.1 15:0 0.7"0.1 16:0 23.0"0.3 Iso-17:0 Tr 17:0 1.9"0.1 18:0 6.0"0.3 20:0 1.1"0.2 22:0 2.3"0.2 24:0 0.7"0.1 S SFA 47.3"0.9
399
Tetraunsaturated fatty acids ( TeUFA ) %
J.-M. Njinkoue´ et al. / Comparative Biochemistry and Physiology Part B 131 (2002) 395–402
B
A
400
Table 4 (Continued) White muscle A
B
C
A
B
C
A
B
C
A
B
C
16:4 v3 18:4 v3 20:4 v6 20:4 v3 S TeUFA
Tr 1.4"0.2 Tr 0.4"0.2 1.8"0.3
Tr 1.0"0.4 Tr 0.3"0.2 1.3"0.4
– 0.3"0.1 Tr 0.3"0.1 0.6"0.2
Tr 1.1"0.1 Tr 0.5"0.1 1.6"0.2
Tr 1.4"0.1 Tr 0.4"0.1 1.8"0.2
– – – – –
– 0.6"0.1 Tr 0.4"0.1 1.0"0.1
– 0.3"0.1 Tr 0.3"0.1 0.6"0.1
– Tr Tr 0.9"0.1 0.9"0.1
– 2.0"0.1 1.0"0.1 0.5"0.1 3.5"0.1
Tr 1.3"0.1 Tr" 0.4"0.1 1.7"0.2
– 0.3"0.1 Tr 0.3"0.1 0.6"0.1
Pentaunsaturated fatty acids ( PeUFA ) % 20:5 v3 11.6"0.2 10.2"0.3 21:5 v3 Tr 0.3"0.1 22:5 v3 1.9"0.1 0.9"0.2 S PeUFA 13.5"0.3 11.4"0.1
4.8"0.1 Tr 1.8"0.1 6.6"0.2
8.3"0.1 – 1.9"0.1 10.2"0.2
14.9"0.1 Tr 1.4"0.1 16.3"0.1
– – – –
4.7"0.1 Tr 1.2"0.1 5.9"0.1
1.8"0.1 – 0.7"0.1 2.5"0.1
1.6"0.1 – 0.5"0.1 2.1"0.1
20.5"0.1 Tr 1.5"0.1 22.0"0.1
10.4"0.1 2.1"0.1 0.8"0.1 13.3"0.3
3.1"0.1 0.6"0.1 2.6"0.1 6.3"0.2
9.3"0.4 0.3"0.1 18.5"0.6 18.2"0.7 17.2"0.6 2.1"0.5
5.4"0.1 0.6"0.1 20.8"0.3 19.7"0.3 18.7"0.3 1.8"0.5
9.7"0.2 0.6"0.2 31.4"0.4 30.1"0.6 29.1"0.5 1.4"0.5
– – – – – –
4.8"0.1 1.1"0.2 15.4"0.4 13.4"0.2 12.6"0.2 2.4"0.6
1.4"0.1 Tr 12.6"0.5 7.5"0.5 5.5"0.3 1.1"0.7
1.1"0.1 1.7"0.1 7.6"0.2 6.5"0.2 6.0"0.2 3.1"0.6
4.2"0.1 0.9"0.3 33.6"0.4 32.5"0.3 30.3"0.2 1.7"0.5
2.5"0.1 0.4"0.1 22.5"0.1 19.9"0.3 18.4"0.4 3.2"0.4
6.9"0.1 0.7"0.2 17.5"0.3 16.9"0.2 15.8"0.4 2.5"0.4
Hexaunsaturated fatty 22:6 v3 S branched FA S PUFA (S v3qS v6) FA S v3 FA S unidentified FA
acids (HUFA 6.9"0.2 0.6"0.1 26.2"0.7 24.3"0.7 23.6"0.8 0.3"0.2
Red muscle
)% 2.5"0.3 1.2"0.2 19.5"0.5 17.4"0.6 16.2"0.4 2.5"0.6
ns5. a C. taeniops is devoid of red muscle.
Liver
Skin
J.-M. Njinkoue´ et al. / Comparative Biochemistry and Physiology Part B 131 (2002) 395–402
Fatty acids
J.-M. Njinkoue´ et al. / Comparative Biochemistry and Physiology Part B 131 (2002) 395–402
tively, 2.5–3.0% of body weight and contains 10.0–70.0% and 8.0–80.0% of lipids (Piclet, 1987). The results found for phospholipid levels in our study (10.0% and 6.0%) are in good agreement with values reported in the literature. For the few species in which lipid class composition was determined, phospholipid rates tended to be higher in those with low lipid content (Maia et al., 1995). The percentages of fatty acids identified differ among species and organs. In red muscle and liver, lipids undergo more enzymatic activities than in smooth muscle, producing large amounts of free fatty acids in oils (Hooper et al., 1973). The high amounts of saturated and monounsaturated fatty acids in our samples are in good agreement with data in the literature. These saturated and monounsaturated fatty acids are generally abundant in fish from warm or temperate regions, whereas PUFA show high levels in fish from cold regions (Dey et al., 1993; Wodtke, 1981). The large amounts of palmitic acid found in our specimens have often been observed. Although EPA content in Sardinella is higher than that of DHA in other species, especially those of temperate or cold regions, DHA is more abundant (Ackman, 1967). The EPA and DHA, still regarded as essential fatty acids and classified among liposoluble vitamins in the past, are the main v3 and v6 polyunsaturated fatty acids. In fish oils, the v6 series generally represents less than 5% of total fatty acids (Ratnayake et al., 1989). The very low amount of arachidonic acid found in the fish studied here could be related to the low percentage of 18:2 v6 in the samples; v3 fatty acid levels were generally higher than those of v6, as is typical for marine fish (Green and Selivonchick, 1987). The amounts of EPA and DHA in the three species studied are comparable to those in fish used for the production and commercialisation of their oils (herring, sardines, menhaden, etc.). This is indicative of their importance as well as the need to study more precisely their lipid composition, according to season, and depending on the effects of storage and processing. Considering the high amounts of polyunsaturated EPA and DHA, these fish would deserve to be better valorised, including liver and skin, in the form of cooking oil for example.
401
Acknowledgments This work was performed in the Laboratory of Phytochemistry, Dakar, in the context of a cooperative program between the University of AixMarseille III and Cheikh Anta Diop University. The GCyMS analyses were performed by Gilbert Nourrisson of the Organic Synthesis Laboratory of the College of Sciences of the University of Nantes, France. References Ackman, R.G., 1967. Characteristics of the fatty acid composition and biochemistry of some fresh water fish oil and lipids in comparison with marine oil and lipids. Comp. Biochem. Physiol. 22, 907–922. Araki, S., Sakurai, T., Omata, T., Kawaguchi, A., Murata, N., 1986. Lipid and fatty acid composition in the red alga ¨ Porphyra yezoensis. Jpn. J. Phycol. (Sorui) 34, 94–100. Belluzi, A., Campieri, M., Brignola, C., Gionchetti, P., Miglioli, M., Barbara, L., 1993. Polyunsaturated fatty acid pattern and oil treatment in inflammatory bowel disease. Gut 34, 1289–1290. Burr, M.L., 1992. Fish food, fish oil and cardiovascular disease. Clin. Exp. Hypertens. A 14, 181–192. Carreau, J.P., Dubacq, J.P., 1978. Adaptation of a macro-scale method to micro-scale for fatty acid methyl transesterification of biological lipid extract. J. Chromatogr. 151, 384–390. ´ ´ ´ Cury, P., Fontana, A., 1988. Competition et strategies demo´ de deux especes ` graphiques comparees de sardinelles (Sarˆ dinella aurita et Sardinella maderensis) des cotes ouest-Africaines. Aquat. Living Resour. 1, 165–180. Dey, I., Buda, C., Wiik, H., Halver, J.E., Farkas, T., 1993. Molecular and structural composition of phospholipid membranes in livers of marine and freshwater fish in relation to temperature. Proc. Ntl. Acad. Sci. USA 90, 7498–7502. Dry, J., Vincent, D., 1991. Effects of fish oil diet on asthma: results of a year double-blind study. Int. Arch. Allergy Appl. Imm. 95, 156–157. Green, D.H.S., Selivonchick, D.P., 1987. Lipid metabolism in fish. Progr. Lipid Res. 26, 53–85. Hodge, L., Salome, C.M., Peat, J.K., Haby, M.M., Xuan, W., Woolcock, A.J., 1996. Consumption of oil fish and childhood asthma risk. Med. J. Aust. 164, 137–140. Hooper, S.N., Paradis, M., Ackman, R.G., 1973. Distribution of trans-6-hexadecenoic acid, 7-methyl-7-hexadecenoic acid and common fatty acids in lipids of the Ocean Sunfish Mola mola. Lipids 11, 247–249. James, M.J., Cleland, L.G., 1996. Dietary polyunsaturated fats and inflammation.. Proceed. Nutr. Soc. Aust. 20, 71–77. Kenneth, C., 1986. Biological effects of fish oil in relation to chronic diseases. Lipids 21, 731–732. Kherunnisa, R.B., Qadri, S., Touheed, A., Viqaruddin, A., 1996. Fatty acid profile of four marine fish species from Karachi coastal waters. J. Chem. Soc. Pak. 18, 44–47. Levine, A.S., Labuza, T.P., 1990. Food systems: the relationship between health and food scienceytechnology. Environ. Health Persp. 86, 233–238.
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Maia, E.L., Amaya, R.D.B., Hotta, L.K., 1995. Fatty acid composition of the neutral and phospholipids of pond-raised Brazilian Piaractus mesopotamicus. Int. J. Food Sc. Techn. 30, 591–597. Millar, J.A., Waal-Manning, H.J., 1992. Fish oil in treatment of hypertension. New Zeal. Med. J. 105, 155. Morris, R.J., Culkin, F., 1989. Fish. In: Ackman, R.G. (Ed.), Marine Biogenic Lipids, Fats and Oils, Vol. I, II. CRC Press, Boca Raton CA, pp. 146–178. Paige, J.A., Liao, R., Hajjar, R.J., Foisy, R.L., Cory, C.R., O’Brien, P.J., Gwathmey, J.K., 1996. Effects of a high omega-3 fatty acid diet on cardiac contractile performance in Oncorhynchus mykyss. Cardiovasc. Res. 31, 249–262. Pham Quang, L., Laur, M.H., 1974. Les lipides polaires de Pelvetia canaliculate (L.) Dech. et Thur. Fucus.. Biochimie 56, 925–935.
´ ˆ Piclet, G., 1987. Le poisson aliment. Composition-interet nutritionnel. Cah. Nutr. Diet. 22, 317–336. Ratnayake, M.W.N., Olson, B., Ackman, R.G., 1989. Novel branched-chain fatty acids in certain fish oils. Lipids 24, 630–637. Rose, D.P., Connoll, J.M., 1993. Effects of dietary omega-3 fatty acids on human breast cancer growth and metastases in nude mice. J. Nat. L. Cancer-Inst. 85, 1743–1747. Wodtke, E., 1981. Temperature adaptation of biological membranes. The effects of acclimatation temperature on the unsaturation of the main neutral and charged phospholipids in mitochondrial membranes of the carp (Ciprinus carpio L.). Biochim. Biophys. Acta 640, 698–709.
Lipids and fatty acids in muscle, liver and skin of three edible fish from the Senegalese coast: Sardinella maderensis, Sardinella aurita and Cephalopholis taeniops Jean-Michel Njinkoue´ a, Gilles Barnathanb,*, Joseph Mirallesc, Emile-Marcel Gaydoud, Abdoulaye Sambe a
´ Departement de Biochimie, Faculte´ des Sciences, Universite´ de Douala, Douala, Cameroun Laboratoire de Chimie Marine, ISOMer, SMAB, UPRES-EA 2160, Universite´ de Nantes, 2, rue de La Houssiniere, BP 92208, F-44322 Nantes Cedex 3, France c ´ Departement de Biologie, Faculte´ des Sciences, Nouakchott, Mauritanie d Laboratoire de Phytochimie, Faculte´ des Sciences, Universite´ Aix-Marseille III, Marseille, France e ´ Laboratoire des Produits Naturels, Departement de Chimie, Faculte´ des Sciences et Techniques, Universite´ Cheikh Anta Diop, ´ ´ Dakar, Senegal b
Received 27 July 2001; received in revised form 12 November 2001; accepted 22 November 2001
Abstract Lipid content and fatty acid composition were determined in three species of edible fish caught in Senegalese waters during the upwelling season (January, 1993). Sardinella maderensis and Sardinella aurita are fat fish containing more than 5% (fresh wt.) of lipids, whereas Cephalopholis taeniops is a lean fish with approximately 1% of lipids. Skin, liver and muscle were studied for each fish species. About 40 fatty acids were identified by GC and GCyMS as methyl esters and N-acyl pyrrolidides. Palmitic acid was the main acid in the muscle and skin of all samples studied (20–33% of total fatty acids). Oleic acid was the main fatty acid in the liver of S. maderensis (27.2%"0.1) and S. aurita (44.7%"0.1). Arachidonic acid was a minor component in all samples. The flesh (muscle) of the three fish species contained high concentrations of v3 polyunsaturated fatty acids (PUFA), ranging from 16.0 to 29.1% and including 20:5 v3 (eicosapentaenoic acid, EPA) and 22:6 v3 (docosahexaenoic acid, DHA) acids as major components. These two acids together accounted for 24.7%"0.1 and 12.9%"0.1 of total acids in the skin of S. maderensis and S. aurita, respectively. The percentages of PUFA found in the fish studied were very similar to those in fish used commercially as sources of PUFA. Muscle sterols, which accounted for 9–11% of total lipids, consisted mainly of cholesterol (up to 97% of total sterols). 䊚 2002 Elsevier Science Inc. All rights reserved. Keywords: Lipid content; Fatty acid composition; Senegalese fish; Sardinella maderensis; Sardinella aurita; Cephalopholis taeniops; Polyunsaturated fatty acids
1. Introduction Fish is a major source of food for mankind, Abbreviations: CC: column chromatography; DHA: docosahexaenoic acid; EPA: eicosapentaenoic acid; GCyMS: Gas chromatographyymass spectrometry; PUFA: polyunsaturated fatty acid; TLC: thin-layer chromatography. *Corresponding author. Tel.: q33-25112-5689; fax: q3324041-2858. E-mail address: [email protected] (G. Barnathan).
providing a significant amount of the animal protein diet in many countries. As compared to red meat, fish flesh is easily digestible because it contains long muscle fibres. Moreover, the consumption of fish has been linked to health benefits, such as reduced risk of coronary heart disease, which are largely attributable to the polyunsaturated fatty acids (PUFA) in fish oils (Morris and Culkin, 1989; Burr, 1992; Paige et al., 1996). A preventive andyor curative effect has also been
1096-4959/02/$ - see front matter 䊚 2002 Elsevier Science Inc. All rights reserved. PII: S 1 0 9 6 - 4 9 5 9 Ž 0 1 . 0 0 5 0 6 - 1
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reported for arterial hypertension (Millar and Waal-Manning, 1992), human breast cancer growth (Rose and Connoll, 1993), inflammatory diseases (Belluzi et al., 1993; James and Cleland, 1996), asthma (Dry and Vincent, 1991; Hodge et al., 1996), and disorders of the immune system (Levine and Labuza, 1990; Kenneth, 1986). These beneficial PUFA can be divided into two biochemical families, v3 and v6, with different biological effects (James and Cleland, 1996). The coast of Senegal and Mauritania, with its vast continental shelf and alternating cold and warm marine currents, is the richest area of West Africa for seafood resources (mainly fish). No detailed chemical studies of the lipid and fatty acid content of these fish are available, even though Sardinella maderensis and S. aurita, two small pelagic fish, constitute a large portion of catches and are the species most often consumed in Senegal. The present study compared these two fat fish (at least 5% of lipidsyfresh wt.) with a lean fish, Cephalopholis taeniops (approximately 1% of lipids), exploited mainly for exportation. There is increasing interest today in fish and fish oils because of their PUFA content. Fish liver has long been a source of oils, (e.g. cod liver oil) for the prevention of vision and growth problems. Liver and skin are often discarded when fish are prepared for consumption, but they were included in this study, together with muscle, to determine their possible nutritional and therapeutic value. As lipid content shows seasonal variations, it seemed appropriate to choose a study period in which fish accumulate the most lipids, i.e. during upwelling when waters highly rich in nutrients and salts rise from the ocean depths to the surface. This study compared the lipid and fatty acid composition of the skin, liver and flesh (white or smooth muscle and red or striped muscle) of the three fish species. 2. Materials and methods The three marine fish species studied, Sardinella maderensis, S. aurita, and Cephalopholis taeniops, are staples of the native fishing industry. The specimens used were purchased fresh at local fish markets in Dakar (Senegal), in January, 1993 during the upwelling period and from July to October during the warm season. Specimens were transported on ice to the laboratory where they were weighed and immediately processed. The specimens were dissected and the organs to be
studied were removed. Water content was determined by drying muscle samples. The organs were extracted separately for total lipids by homogenisation in a Waring blender for 2 min with a mixture of CH2Cl2 yMeOH (1:1, vyv). The crude extract was split into two parts. The first was chromatographed on an open silica gel column to obtain the different lipid classes by the usual methods (Pham Quang and Laur, 1974; Araki et al., 1986). Phospholipid composition was analysed by thin-layer chromatography (TLC) using chloroformymethanolywater (65:25:4, vyv) as eluent. Silica gel 60-W plates (Merck) with a size of 20=20 cm and a layer thickness of 0.25 mm were used. Glycolipid composition was analysed by TLC according to Araki et al. (1986). Silica gel (70–230 mesh) column chromatography (CC) was performed with hexane, chloroform (neutral lipids), acetone (glycolipids) and methanol (phospholipids) as successive eluents. Glycolipid and phospholipid classes were quantified by preparative TLC. The second part of the crude extract was saponified (KOHyEtOH, 2 M), for 2 h under reflux. The fatty acids obtained were converted into methyl esters by reaction (30 min under reflux) with methanolic hydrogen chloride, dissolved in hexane (Carreau and Dubacq, 1978) and purified by silica gel CC with hexaneydiethyl ether (10:1, vyv) as eluent or by thin-layer chromatography (TLC) with the same eluent. The resulting methyl esters were firstly analysed by gas chromatography (GC) using a Carlo-Erba 4130 chromatograph, a non-polar OV-1 silica capillary column (25 m=0.32 mm i.d., 0.4-mm film thickness) or a polar Carbowax 20 M silica capillary column (50 m=0.32 mm i.d., 0.4-mm film thickness). The carrier gas was hydrogen (0.6 bars, split 5y100). Column temperature was programmed from 190 8C to 230 8C at 2 8Cymin. Nacyl pyrrolidides were prepared by direct treatment of methyl esters with pyrrolidineyacetic acid (10:1, vyv) for 2 h under reflux and purified by TLC on 0.5-mm silica gel layers, using hexaney diethyl ether (1:2, vyv) as developing solvent. GCyMS analyses of methyl esters and N-acyl pyrrolidides were performed on a Hewlett-Packard HP-5890 (GC) and 5989A instrument (MS) linked to an HP 9000y345 integrator. The GC column was a 30 m=0.32 mm i.d. fused silica capillary column coated with non-polar DB-1 (0.25-mm film thickness). The carrier gas was helium. Column
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397
Table 1 Total lipid content (% of fresh wt.) in the organsa of studied fish Fish
Skin
Liver
White muscle
Red muscle
S. maderensis S. aurita C. taeniops
26.0 (0.6) 24.0 (0.8) 2.4 (0.3)
10.0 (0.9) 12.0 (0.9) 8.0 (0.6)
5.0 (0.7) 3.5 (0.4) 1.3 (0.2)
21.0 (0.9) 10.0 (0.9) –b
ns10. S.D. in brackets. a White muscle is the major organ component, followed by red muscle, skin and liver. b C. taeniops is devoid of red muscle.
temperature was programmed from 180 to 300 8C at 3 8Cymin in order to get the better resolution. The detector and injector temperature was 250 8C. Total sterols were extracted from unsaponifiable fraction by silica gel column using chloroform as eluent and analysed as acetates by GC under the following conditions: OV-1 column as described above, hydrogen as carrier gas, and a column temperature of 230 8C. The detector and injector temperature was 250 8C. Data statistical analysis was carried out with a Sigmastat software (version 2.03). Data were subjected to Student’s t-test for determining significant differences between means. Each sample lot consisted of six fish. Data are expressed as mean"S.D., n values are given for each Table. 3. Results Table 1 shows the lipid content of different parts (skin, liver, muscle) of the three edible fish species studied during the same upwelling period. Lipid content ranged from 1.3%"0.2 (white muscle of C. taeniops) to 26.0%"0.6 (skin of S. maderensis). As shown in Table 1, S. maderensis contained more lipids than S. aurita, especially in red muscle (twice as much). Red muscle of the Sardinella species contained more lipids than white muscle: approximately 3 times as much in S. aurita and 4 times as much in S. maderensis. Both Sardinella species had similar lipid content in skin. Lipid content in liver was also similar in the Sardinella
species. C. taeniops, which is devoid of striped muscle, had much lower lipid content than the two Sardinella species. The lipids of C. taeniops were concentrated particularly in liver, which contained more than muscle and skin. The liver of the three fish species contained 8.0%"0.6 to 12.0%"0.9 of total lipids and represented 1.1%"0.2 to 2.0%"0.5 of total body weight: 1.1%"0.2 of body weight and 8.0%"0.6 of lipids for C. taeniops; 2.0%"0.5 and 12.0%"0.9, respectively for S. aurita; and 1.5%"0.2 and 10.0%"0.9, respectively for S. maderensis. The following values were obtained from the Student’s t-test for each organ from both Sardinella species: for skin, ts 6.382, d.f. (degree of freedom)s18, P-0.001; for liver, ts4.940, d.f. s18, P-0.001; for white muscle, ts5.590, d.f.s18, P-0.001; and for red muscle, ts28.194, d.f.s18, P-0.001. A significant difference (P-0.001) was found between the lipid contents in Sardinella. Therefore, a significant difference was also found between Sardinella and C. taeniops. Lipid content differed according to season. In the warm season, when waters were poor in nutrients and mineral salts, the value ranged from 2.8"0.2 to 4.0%"0.2 in white muscle of the two Sardinella species and was F0.8%"0.2 in C. taeniops muscle. Lipid content differed not only from one organ to another, but also inversely to water content. For example, the water content for C. taeniops was 68.8%"0.4 in liver, 73.3%"0.5
Table 2 Water content (%) of the fish muscles and liver C. taeniops
S. maderensis
Muscle 80.0"0.8
White muscle 72.0"0.7
Liver 68.8"0.4
71.2"0.5
ns10.
S. aurita Red muscle 65.0"0.6
White muscle 73.0"0.6 73.7"0.6
Red muscle 68.0"0.9
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Table 3 Sterol content and composition of white muscle in the three fish species Fish species
Sterol contenta
Cholesterolb
Campesterolb
S. maderensis S. aurita C. taeniops
9.8"0.5 9.5"0.4 10.8"0.5
97.0"0.8 98.0"0.4 99.3"0.3
3.0"0.2 2.0"0.2 0.3"0.1
ns5. a As a percentage of total lipids. b As a percentage of total sterols.
in skin and 80.0%"0.8 in muscle. Table 2 shows the water content in the muscles and in the liver of both Sardinella and C. taeniops. The Student’s t-test showed a significant difference between water contents in fish muscles: ts3.388, d.f.s18, Ps0.003 for the white muscle; and ts8.321, d.f.s18, P-0.001 for the red muscle. The average total lipid fraction in white muscle contained 10.0"0.4 to 15.0"0.5% polar lipids. The major phospholipid classes were shown to be phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol, and the major glycolipid classes were shown to be monogalactosyldiglyceride and digalactosyldiglyceride, as judged by TLC analysis in the three fish. Phospholipids accounted for 10.0"0.1% and 6.0"0.2% of total white muscle lipids in C. taeniops and both Sardinella species, respectively. It was observed that phospholipid content tended to be higher in fish with low lipid content. Unsaponifiable matter represented 17–19% of the fish total lipids. Sterols accounted for approximately 56% of the unsaponifiable matter in the three fish. As shown in Table 3, the sterol content in lipids of white muscle (the major site) was 9.8%"0.5 of total lipid weight in S. maderensis, 9.5%"0.4 in S. aurita and 10.8%"0.5 in C. taeniops. Two sterols were only present in all cases, namely campesterol and cholesterol as the major sterol (97–99%). Fatty acids represented 60.0–70.0% of total lipid weight in the three fish species. Approximately 40 fatty acids were characterised as methyl esters and N-acyl pyrrolidides by GC and GCyMS. Table 4 shows the fatty acid profiles of the three fish species, which are listed in the order of chromatographic retention time and the number of their carbons and unsaturations. The main acid in all samples analysed was palmitic acid (20.0–33.0% of total fatty acids), except in the liver of S.
maderensis and S. aurita where oleic acid was the main acid, accounting for 26.0% and 44.0% of fatty acids, respectively. Arachidonic acid was a minor compound in all fatty acid mixtures analysed. Saturated fatty acids accounted for 32.0– 58.0% in the different fatty acid mixtures. These species of fish are poor in branched fatty acids and no isoprenoid fatty acid was detected. An interesting result of this study was the content found for v3 PUFA, which ranged from 16.0 to 32.0%. The 20:5 v3 (EPA) and 22:6 v3 (DHA) acids were major components of the series in flesh and skin of the three fish species. The flesh and skin of all three species contained a similar percentage of saturated fatty acids, whereas the liver of C. taeniops contained more saturated fatty acids than those of the two Sardinella species. All specimens showed low amounts of v6 PUFA. 4. Discussion The two Sardinella species are closely related, have a similar diet and occupy the same geographical areas. The growth and reproductive patterns of both species, as well as their exploitation as food resources, are highly influenced by the dynamics of upwelling systems (Cury and Fontana, 1988). These common edible fish were caught in Senegalese waters in January, 1993 during the upwelling period. Along the coasts of Senegal and Mauritania, S. maderensis is richer in lipids than S. aurita, whereas along the Congolese coasts the curve for monthly variations in the fatty acid content of S. aurita remains above that of S. maderensis throughout the year (Cury and Fontana, 1988). In the warm season (July to October), when waters are poor in nutrients and mineral salts, lipid content decreases considerably, dropping to 2.8%, and G0.8% in the muscle of S. aurita and C. taeniops, respectively. In fat fish, the lipid content of both types of muscle is richer in older animals. The considerable variation in lipid content reported in many studies on fish in different areas around the world is apparently due to factors such as season, temperature, diet, age, size and sex (Kherunnisa et al., 1996). Compared to the oil content of muscle, the liver of C. taeniops contains significant lipid content. However, this liver content is low compared to that of other lean fish, such as the cod and certain shark species in which the liver represents, respec-
Table 4 Fatty acid composition (% total fatty acids) of total lipids from three Senegalese fish species: Sardinella maderensis (A), S. aurita (B) and Cephalopholis taeniops (C)a Fatty acids
White muscle
Red muscle
Liver
Skin
C
A
B
C
A
B
C
A
B
C
7.8"0.2 0.5"0.1 0.7"0.1 23.2"0.5 Tr 1.8"0.1 6.2"0.2 0.6"0.1 2.5"0.3 0.3"0.1 43.6"0.5
4.0"0.1 0.3"0.1 0.4"0.1 31.4"0.1 Tr 1.2"0.1 10.5"0.4 0.5"0.1 0.3"0.1 0.8"0.1 49.4"0.2
8.3"0.1 Tr 0.6"0.1 25.6"0.1 Tr 1.8"0.1 6.4"0.1 0.9"0.1 3.1"0.1 0.8"0.1 47.5"0.5
5.9"0.1 0.3"0.1 0.6"0.1 23.1"0.1 Tr 1.4"0.1 6.4"0.1 0.8"0.1 1.8"0.1 0.3"0.1 40.6"0.5
– – – – – – – – – – –
3.2"0.1 0.3"0.1 0.3"0.1 25.6"0.1 0.3"0.1 1.1"0.1 5.4"0.1 0.3"0.1 0.5"0.1 1.0"0.1 38.0"0.3
2.0"0.1 – 0.3"0.1 23.2"0.2 Tr 0.3"0.1 5.0"0.1 0.3"0.1 0.9"0.2 0.3"0.1 32.3"0.5
9.2"0.1 1.7"0.1 2.4"0.1 33.9"0.1 Tr 1.4"0.1 9.2"0.1 0.3"0.1 0.5"0.1 Tr 58.6"0.3
8.1"0.1 0.3"0.1 0.5"0.1 20.5"0.2 0.3"0.1 2.0"0.1 5.8"0.1 1.2"0.1 2.3"0.1 0.5"0.1 41.5"0.4
7.8"0.1 0.4"0.1 0.6"0.1 20.5"0.1 Tr 1.8"0.1 5.6"0.1 0.8"0.1 2.5"0.1 0.3"0.1 40.3"0.2
5.0"0.1 0.3"0.1 0.7"0.1 28.4"0.2 0.4"0.1 1.0"0.1 8.4"0.1 0.3"0.1 0.3"0.1 1.6"0.1 46.4"0.4
Monounsaturated fatty acids (MUFA) % 16:1 v8 0.4"0.1 0.7"0.2 18:1 v7 9.2"0.2 9.5"0.1 7-Me-16:1v10 Tr 0.7"0.1 17:1 v9 1.1"0.1 1.0"0.1 18:1 v9 7.7"0.2 14.4"0.2 18:1 v7 4.4"0.1 5.1"0.5 20:1 v12 0.3"0.1 0.3"0.1 20:1 v9 1.9"0.1 1.4"0.4 20:1 v7 0.4"0.1 Tr 22:1 v11 Tr 0.3"0.2 24:1 v9 0.8"0.1 1.0"0.2 S MUFA 26.5"0.5 34.4"0.9
0.5"0.1 9.5"0.1 – 0.6"0.1 11.6"0.1 5.3"0.2 0.3"0.1 1.2"0.1 0.3"0.1 0.3"0.1 1.0"0.1 30.6"0.4
0.6"0.1 8.1"0.1 0.6"0.1 0.8"0.1 10.4"0.1 4.9"0.1 0.4"0.1 2.8"0.1 0.4"0.1 0.4"0.1 0.5"0.1 29.9"0.5
– 6.1"0.1 0.3"0.1 0.8"0.1 13.7"0.1 4.0"0.1 0.3"0.1 1.4"0.1 Tr Tr Tr 26.6"0.4
– – – – – – – – – – – –
0.7"0.1 3.9"0.1 0.5"0.1 0.3"0.1 27.2"0.1 6.6"0.1 0.4"0.1 3.2"0.1 0.5"0.1 0.6"0.1 0.3"0.1 44.2"0.6
0.6"0.1 2.6"0.1 Tr Tr 44.7"0.2 4.0"0.1 0.4"0.1 1.7"0.1 Tr Tr Tr 54.0"0.1
0.8"0.1 16.4"0.1 – 0.5"0.1 8.6"0.1 3.4"0.1 1.0"0.1 – Tr – – 30.7"0.2
– 8.0"0.1 0.3"0.1 1.4"0.1 8.2"0.1 3.1"0.1 1.9"0.1 – 0.3"0.1 Tr Tr 23.2"0.3
0.4"0.1 10.1"0.1 Tr 1.2"0.1 15.5"0.1 4.2"0.1 0.3"0.1 1.6"0.2 0.3"0.1 0.4"0.1 Tr 34.0"0.3
1.2"0.1 11.8"0.1 Tr 0.3"0.1 12.5"0.1 4.3"0.2 Tr 1.5"0.1 0.3"0.2 1.7"0.1 Tr 33.6"0.4
Diunsaturated fatty acids ( DUFA ) % 18:2 v6 0.3"0.2 0.7"0.2 18:2 0.9"0.1 0.6"0.1 20:2 v9 0.7"0.1 1.1"0.2 S DUFA 1.9" 2.4"0.2
0.7"0.1 – Tr 0.7"0.1
1.0"0.1 0.5"0.1 Tr 1.5"0.1
0.6"0.1 0.4"0.1 0.9"0.1 1.9"0.1
– – – –
0.5"0.1 0.5"0.1 0.7"0.1 1.7"0.3
1.7"0.1 0.3"0.1 4.3"0.1 6.3"0.2
0.5"0.1 Tr 0.3"0.1 0.8"0.2
1.2"0.1 0.7"0.1 0.3"0.1 2.2"0.1
0.7"0.1 0.8"0.1 1.2"0.1 2.7"0.2
0.8 0.3 Tr 1.1
Triunsaturated fatty acids ( TrUFA ) % 16:3 v4 0.3"0.2 0.4"0.2 18:3 v6 0.4"0.1 0.5"0.3 18:3 Tr Tr 18:3 v3 0.3"0.1 0.3"0.2 20:3 v3 1.1"0.2 0.7"0.2 S TrUFA 2.1"0.3 1.9"0.5
Tr 0.3"0.2 0.3"0.1 Tr 0.7"0.1 1.3"0.2
0.3"0.1 Tr 0.3"0.1 0.5"0.1 1.0"0.1 2.1"0.2
Tr 0.4"0.1 Tr 0.4"0.1 0.9"02 1.7"0.1
– – – – – –
0.4"0.1 0.3"0.1 0.4"0.1 0.4"0.1 0.5"0.1 2.0"0.3
0.5"0.1 0.3"0.1 Tr 0.7"0.1 0.3"0.1 1.8"0.4
0.8"0.1 Tr – 0.9"0.1 1"0.1 2.7"0.2
Tr 0.3"0.1 0.8"0.1 0.3"0.1 0.3"0.1 1.7"0.2
0.3"0.1 0.8"0.1 0.3"0.1 0.3"0.1 0.6"0.1 2.3"0.2
Tr 0.3"0.1 0.3"0.1 0.3"0.1 1.7"0.1 2.6"0.3
Saturated fatty acids ( SFA) % 14:0 11.0"0.6 Iso-15:0 0.6"0.1 15:0 0.7"0.1 16:0 23.0"0.3 Iso-17:0 Tr 17:0 1.9"0.1 18:0 6.0"0.3 20:0 1.1"0.2 22:0 2.3"0.2 24:0 0.7"0.1 S SFA 47.3"0.9
399
Tetraunsaturated fatty acids ( TeUFA ) %
J.-M. Njinkoue´ et al. / Comparative Biochemistry and Physiology Part B 131 (2002) 395–402
B
A
400
Table 4 (Continued) White muscle A
B
C
A
B
C
A
B
C
A
B
C
16:4 v3 18:4 v3 20:4 v6 20:4 v3 S TeUFA
Tr 1.4"0.2 Tr 0.4"0.2 1.8"0.3
Tr 1.0"0.4 Tr 0.3"0.2 1.3"0.4
– 0.3"0.1 Tr 0.3"0.1 0.6"0.2
Tr 1.1"0.1 Tr 0.5"0.1 1.6"0.2
Tr 1.4"0.1 Tr 0.4"0.1 1.8"0.2
– – – – –
– 0.6"0.1 Tr 0.4"0.1 1.0"0.1
– 0.3"0.1 Tr 0.3"0.1 0.6"0.1
– Tr Tr 0.9"0.1 0.9"0.1
– 2.0"0.1 1.0"0.1 0.5"0.1 3.5"0.1
Tr 1.3"0.1 Tr" 0.4"0.1 1.7"0.2
– 0.3"0.1 Tr 0.3"0.1 0.6"0.1
Pentaunsaturated fatty acids ( PeUFA ) % 20:5 v3 11.6"0.2 10.2"0.3 21:5 v3 Tr 0.3"0.1 22:5 v3 1.9"0.1 0.9"0.2 S PeUFA 13.5"0.3 11.4"0.1
4.8"0.1 Tr 1.8"0.1 6.6"0.2
8.3"0.1 – 1.9"0.1 10.2"0.2
14.9"0.1 Tr 1.4"0.1 16.3"0.1
– – – –
4.7"0.1 Tr 1.2"0.1 5.9"0.1
1.8"0.1 – 0.7"0.1 2.5"0.1
1.6"0.1 – 0.5"0.1 2.1"0.1
20.5"0.1 Tr 1.5"0.1 22.0"0.1
10.4"0.1 2.1"0.1 0.8"0.1 13.3"0.3
3.1"0.1 0.6"0.1 2.6"0.1 6.3"0.2
9.3"0.4 0.3"0.1 18.5"0.6 18.2"0.7 17.2"0.6 2.1"0.5
5.4"0.1 0.6"0.1 20.8"0.3 19.7"0.3 18.7"0.3 1.8"0.5
9.7"0.2 0.6"0.2 31.4"0.4 30.1"0.6 29.1"0.5 1.4"0.5
– – – – – –
4.8"0.1 1.1"0.2 15.4"0.4 13.4"0.2 12.6"0.2 2.4"0.6
1.4"0.1 Tr 12.6"0.5 7.5"0.5 5.5"0.3 1.1"0.7
1.1"0.1 1.7"0.1 7.6"0.2 6.5"0.2 6.0"0.2 3.1"0.6
4.2"0.1 0.9"0.3 33.6"0.4 32.5"0.3 30.3"0.2 1.7"0.5
2.5"0.1 0.4"0.1 22.5"0.1 19.9"0.3 18.4"0.4 3.2"0.4
6.9"0.1 0.7"0.2 17.5"0.3 16.9"0.2 15.8"0.4 2.5"0.4
Hexaunsaturated fatty 22:6 v3 S branched FA S PUFA (S v3qS v6) FA S v3 FA S unidentified FA
acids (HUFA 6.9"0.2 0.6"0.1 26.2"0.7 24.3"0.7 23.6"0.8 0.3"0.2
Red muscle
)% 2.5"0.3 1.2"0.2 19.5"0.5 17.4"0.6 16.2"0.4 2.5"0.6
ns5. a C. taeniops is devoid of red muscle.
Liver
Skin
J.-M. Njinkoue´ et al. / Comparative Biochemistry and Physiology Part B 131 (2002) 395–402
Fatty acids
J.-M. Njinkoue´ et al. / Comparative Biochemistry and Physiology Part B 131 (2002) 395–402
tively, 2.5–3.0% of body weight and contains 10.0–70.0% and 8.0–80.0% of lipids (Piclet, 1987). The results found for phospholipid levels in our study (10.0% and 6.0%) are in good agreement with values reported in the literature. For the few species in which lipid class composition was determined, phospholipid rates tended to be higher in those with low lipid content (Maia et al., 1995). The percentages of fatty acids identified differ among species and organs. In red muscle and liver, lipids undergo more enzymatic activities than in smooth muscle, producing large amounts of free fatty acids in oils (Hooper et al., 1973). The high amounts of saturated and monounsaturated fatty acids in our samples are in good agreement with data in the literature. These saturated and monounsaturated fatty acids are generally abundant in fish from warm or temperate regions, whereas PUFA show high levels in fish from cold regions (Dey et al., 1993; Wodtke, 1981). The large amounts of palmitic acid found in our specimens have often been observed. Although EPA content in Sardinella is higher than that of DHA in other species, especially those of temperate or cold regions, DHA is more abundant (Ackman, 1967). The EPA and DHA, still regarded as essential fatty acids and classified among liposoluble vitamins in the past, are the main v3 and v6 polyunsaturated fatty acids. In fish oils, the v6 series generally represents less than 5% of total fatty acids (Ratnayake et al., 1989). The very low amount of arachidonic acid found in the fish studied here could be related to the low percentage of 18:2 v6 in the samples; v3 fatty acid levels were generally higher than those of v6, as is typical for marine fish (Green and Selivonchick, 1987). The amounts of EPA and DHA in the three species studied are comparable to those in fish used for the production and commercialisation of their oils (herring, sardines, menhaden, etc.). This is indicative of their importance as well as the need to study more precisely their lipid composition, according to season, and depending on the effects of storage and processing. Considering the high amounts of polyunsaturated EPA and DHA, these fish would deserve to be better valorised, including liver and skin, in the form of cooking oil for example.
401
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