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JOURNAL OFFOOD COMPOSITION

AND ANALYSIS

Journal of Food Composition and Analysis 18 (2005) 717–722

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Short Communication

Fatty acid composition of oil extracted from Nile perch(Lates niloticus) head

Fabrice Turona,�, Brian Rwabwogob, Bruno Bareac, Michel Pinac, Jean Graillec

aBERTIN, Route de Mareuil, BP 51, 60330 Lagny-le-Sec, FrancebRECO Industries Limited, Plot 25, Nkrumah Rd., P.O. Box 257 Kampala, Uganda

cCIRAD/AMIS, Laboratoire de Lipotechnie, TA 40/16, F 34398 Montpellier Cedex, France

Received 6 October 2003; received in revised form 12 July 2004; accepted 19 July 2004

Abstract

Oil was extracted from Nile perch (Lates niloticus) head collected from the Victoria Lake (Uganda). Oilcontent was in the range 15–18% of dry weight. The predominant fatty acids found in crude oil were 14:0,16:0, 16:1, 17:0, 18:0, 18:1, 18:2, 18:3, 20:4, 20:5, 22:5 and 22:6. The crude Nile perch oil contained asubstantial amount of oleic acid (15.2mol%) and an appreciable level of combined n-3 polyunsaturatedfatty acids (16.2mol%). Comparing with the commercial production of fish oils, oil from Nile perch headsmight stimulate its future use for human consumption and easily could be valorized.r 2004 Elsevier Inc. All rights reserved.

Keywords: Lake Victoria; Lates niloticus; Nile perch; Head; Triacylglycerols; Fatty acid; Regiodistribution

1. Introduction

Formerly called Nile perch, the Lake Victoria perch (Lates niloticus) is a freshwater fish foundin central Africa’s lakes and rivers. In the 1960s, the perch was first introduced to Lake Victoria tocurb the growth of other species and develop a sport fishery (Fryer, 1960). Due to its ecologicaltenacity, this voracious predator now accounts for approximately two thirds of the lake’s

see front matter r 2004 Elsevier Inc. All rights reserved.

jfca.2004.07.003

ding author. Tel.: +33-344-608-927: fax: +33-344-608-076.

ress: huiles-michelbertin@wanadoo.fr (F. Turon).

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population (Ogutu-Ohwayo, 1990; Wanink and Goudswaard, 1994). Nile perch has become themost abundant species in commercial catches, with the prospect of a virtually continuous supply.Uganda’s fish catch is about 220 thousand metric tons per year. The tonnage of perch annuallyexported head off increased from 8.5 thousand metric tons in 1999 to approximately 14.7thousand metric tons in 2000. Fillets find their way to diners in Europe; shoes, belts and purses aremade from tanned perch hide; dried swim bladders are sent to England for filtering beer and wineand to Orient for making soup stock (Rogers and Mosille, 1990; Tall, 1990). In contrast, most ofthe fish heads are not exported but sold locally or wasted. Accordingly, we tried to valorize the L.

niloticus heads by extracting oil content. The fatty acid composition, including their positionaldistribution and oxidative status of L. niloticus head oil are discussed in terms of the nutritionalvalue as a large body of work has been reported on the docosahexaenoic (DHA) (22:6) andeicosapentaenoic acid (EPA) (20:5) content of some freshwater tropical fish (Zenebe et al., 1998;Simopoulos, 1989).

2. Materials and methods

Nile Perch head and chemicals. Ten heads from Nile perch (about 1.02 kg per heads) werecollected on July from a local market in Uganda. Ethyl magnesium bromide 3.0M solution indiethyl ether and a methanolic solution of BF3 (10%wt/vol) were obtained from Aldrich(Milwaukee, USA). All organic solvents were purchased from Merck (Darmstadt, Germany).

Oil extraction. The oil from the fish head was extracted mainly according to the followingprocedure. Ten heads were roughly crushed in a mincing machine. The crushed heads were mixedwith water (20%wt/vol) and heated at 50 1C for 30min. The upper phase was drained, and the oilin the water was centrifuged until a separation of those two phases. The oil which was collected inthe surface liquid was weighed.

Regiodistribution analysis of triacylglycerols (TAG). The regiodistribution analysis of TAG wasperformed after degradation to partial acylglycerols with ethyl magnesium bromide (Turon et al.,2002). The resulting mixture of partial acylglycerols was separated by preparative thin-layerchromatography. The plates were developed with a chloroform/acetone/acetic acid solution(85:15:1, by vol). The a-monoacylglycerols (a-MAG) band was visualized under ultraviolet light(Rf ¼ 0:26) and scrapped off. The a-MAG were converted to fatty acid methyl esters (FAME) andanalyzed by GLC. The fatty acid composition in the b position was obtained by calculation from3�TAG minus 2� a-MAG.

FAME preparation. FAME were prepared according to Morrison and Smith (1964). To twodrops of oil, introduced in a Teflon-lined screw-capping tube, was added 1mL of a methanolicsolution of BF3 (10%wt/vol), and the mixture was homogenized with 1mL of hexane. The tubeswere tightly capped, and the methylation was performed at 100 1C for 60min. FAME wereextracted twice with 1mL hexane, with water (1mL) being added to the mixture.

Gas–liquid chromatography (GLC). Analysis of FAME was performed using a Carlo Erba GC6000 Vega Serie 2 chromatograph (Carlo Erba, Milan, Italy) equipped with a fused-silica capillarycolumn (CP-Sil 88, 50m� 0.22mm i.d., 0.2 mm film; Chrompack, Middelburg, The Netherlands).The oven was heated from 150 to 225 1C by 5 1Cmin�1 and held for 10min, while the injector(split mode) and the flame-ionization detector were maintained at 250 1C. The inlet pressure of

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carrier gas (hydrogen) was 85 kPa. Quantitative data were given by a D-2500 integrator (Merck,Darmstadt, Germany). Peak area percentages obtained with the integrator were divided bymolecular weight of individual FAME to yield moles per cent of fatty acids. Two GC analyses ofproducts from four experiments were made.

Determination of free fatty acid content (FFA). FFA was determined by titration with NaOH0.1mol/L solution using phenolphthalein as an indicator (AOCS, 1989). The amount of FFAswas calculated as wt% oleic acid. Analyses were made in duplicate.

Determination of peroxide value (PV). PV expressed as meq O2/kg oil was measured accordingto the American Oil Chemists’ Society official method Method Cd 8b-90 (AOCS, 1998). Analyseswere made in duplicate.

Determination of anisidine value (AnV). AnV was determined spectrophotometrically by AOCSmethod Method Cd 18-90 (AOCS, 1994). Analyses were made in duplicate.

3. Results and discussion

Material balance. An average of 10.2 kg of whole L. niloticus heads was required to produce1.8 kg of crude oil which corresponds to an oil content of 15–18% of dry weight. Crude oilcontained a low amount of FFA (1.070.1% oleic acid) and its oxidative status is quite acceptablefor a non-refined oil (PV=5.270.2meqO2/kg; AnV ¼ 3:7� 0:1). According to the CodexAlimentarius, criteria of quality for a crude oil are a FFA content of 2% and a PV lower than15meqO2/kg (CODEX STAN, 19—1981, 1999).

FA composition. The FA composition and its corresponding GC profile are shown in Table 1and Fig. 1, respectively. The 12 major FA (41mol%) found in crude Nile perch oil included 14:0,16:0, 16:1, 17:0, 18:0, 18:1, 18:2, 18:3, 20:4, 20:5, 22:5 and 22:6. The saturated FA accounted for39.9mol%; comparable contents were observed in freshwater fish from tropical lakes (Zenebe etal., 1998). Palmitic acid was the pre-dominant FA in L. niloticus crude oil, accounting for about60% of all saturated FA. The total unsaturated FA content was greater than that of the totalsaturated FA and amounted to 57.3mol%. Among unsaturated FA, oleic and palmitic acids werethe pre-dominant FA, accounting for almost 26% and 24% of total unsaturated FA, respectively.In contrast, oleic and palmitic acids values reported for tropical fish (Zenebe et al., 1998) werefour times lower than those of the Nile perch oil. The polyunsaturated fatty acids (PUFA) areconsidered to be of major importance in terms of human health. The crude L. niloticus oilcontained 6.5 and 3.0mol% of DHA and EPA, respectively. Combined n-3 PUFA (18:3, 20:5,22:5 and 22:6) accounted for 16% of total FA. Freshwater fish are capable of performing theconversion of linolenic acid to the longer n-3 PUFA by chain elongation and desaturation(Henderson and Tocher, 1987). Accordingly, PUFA levels in the fish examined (57.3%) werehigher than those observed in many tropical fish. A reported level of PUFA in tropical freshwaterfish is between 5.8% and 29.5% (Zenebe et al., 1998).

Positional distribution. The regiospecific analysis of L. niloticus head oil is presented in Table 1.The saturated 14:0 and 16:0 were low in the a position, whereas 70% and 90% of the acids 17:0and 18:0, respectively, were esterified in this position. The unsaturated FA were preferentiallyesterified in the a position. The contents of 16:1, 18:1, 18:3, EPA and 22:5 in the a position were62%, 88%, 78%, 75% and 56%, respectively. Fifty seven percent of DHA, however, was located

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1

2

3 4

5

6

7

8

9

10

11

12

131415

16

17

min

18

19

20

2122

23 24

25

26

27

29

2830

31

32

33

34 35

Fig. 1. Typical chromatogram of fatty acid methyl esters prepared from the oil extracted from Nile perch heads.

Analysis on a CP-Sil 88 capillary column (50m� 0.22mm i.d., 0.2 mm film; Chrompack, Middelburg, The Netherlands)

operated from 150 to 225 1C by 5 1Cmin�1 and held for 10min, with an inlet carrier gas (hydrogen) pressure of 85 kPa.

Peak identification: 1, 12:0; 2, 14:0; 3, 15 iso; 4, 15:0; 5, 16 iso; 6, 16:0; 7, 17 iso; 8, 16:1; 9, 17:0; 10, 18 iso; 11, 17:1; 12,

unknown; 13, 18:0; 14, 9–18:1; 15, 11–18:1; 16, 9,12–18:2; 17, 20:0; 18, 6,9,12–18:3; 19, 20:1; 20, 9,12,15–18:3; 21,

6,9,12,15–18:4; 22, 11,14–20:2; 23, 22:0; 24, 8,11,14–20:3; 25, unknown; 26, 5,8,11,14–20:4; 27, 8,11,14,17–20:4; 28, 24:0;

29, 5,8,11,14,17–20:5; 30, 15–24:1; 31, 7,10,13,16–22:4; 32, unknown; 33, 4,7,10,13,16–22:5; 34, 7,10,13,16,19–22:5; 35,

4,7,10,13,16,19–22:6. Double bonds are in the cis configuration.

F. Turon et al. / Journal of Food Composition and Analysis 18 (2005) 717–722720

in the b position. This distribution pattern resembles that observed for tuna head oil in the reportsof Ando et al. (1996, 2000). The analytical method used in the previous studies involved theseparation and HPLC elution profiles of a- and b-MAG generated by Grignard hydrolysis ofTAG. Presently, our study was based on TLC separation and GC analysis of a-MAG formedfrom TAG (Turon et al., 2002).

4. Conclusions

In summary, the results of the present study confirm the possibility for commercial andindustrial exploitation of heads from Nile perch. The fishery of Lake Victoria is of incalculableworth as a source of fish. Traditionally, the heads of Nile perch were usually wasted. Oil couldeasily be extracted from these heads by crushing, heating and decanting oil in water. This type ofextraction leads to a crude oil and palatable fish protein, which is easily available for theindigenous population. Oil extracted from the fish head contained significant amounts of oleic

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Table 1

Fatty acid composition and distribution (from a to b positions) of oil from Nile perch heads (as mol%)

Fatty acida Fatty acid profileb (mol%) Fatty acid distributionb (mol%)

a position b position

12:0 0.1670.05 0.2470.03 —7—

14:0 4.3670.09 2.7870.71 7.5270.40

15:0 iso 0.6970.02 0.4770.06 1.1270.06

15:0 0.7670.07 0.5870.03 1.1470.10

16:0 iso 0.2970.01 0.2070.02 0.4670.03

16:0 23.770.26 19.170.99 33.070.62

17:0 iso 0.5170.07 0.4770.05 0.4070.06

16:1c 13.970.13 13.070.25 15.870.20

17:0 1.4970.14 1.6170.02 1.2770.08

18:0 iso 0.1570.01 0.1370.02 0.2170.02

17:1 0.8870.01 0.9570.04 0.7270.03

18:0 7.0170.41 9.6270.74 1.7870.21

9–18:1 15.270.43 20.070.59 5.5170.51

11–18:1 4.5970.13 5.7870.42 2.2070.20

9,12–18:2 2.2370.02 2.5670.23 1.5970.12

20:0 0.3770.02 0.5570.01 —7—

6,9,12–18:3 0.2670.02 0.2770.02 0.2270.03

20:1c 0.6370.05 0.6170.03 0.6870.11

9,12,15–18:3 2.2670.09 2.6570.14 1.4970.11

6,9,12,15–18:4 0.2370.03 0.1170.01 0.5870.06

11,14–20:2 0.2070.02 0.2670.03 0.1070.02

22:0 0.2370.03 0.3470.07 0.0370.00

8,11,14–20:3 0.2670.03 0.4270.04 —7—

5,8,11,14–20:4 1.6570.04 1.6470.02 1.6870.03

8,11,14,17–20:4 0.3470.03 0.5170.05 —7—

24:0 0.1170.01 0.1470.02 0.1970.01

5,8,11,14,17–20:5 3.0070.29 3.3370.50 2.3570.22

15–24:1 0.2170.02 0.1670.01 0.3170.04

7,10,13,16–22:4 0.4870.03 0.5670.07 0.3170.05

4,7,10,13,16–22:5 0.8170.02 0.7970.04 0.8370.03

7,10,13,16,19–22:5 3.8770.01 3.2070.13 5.2170.07

4,7,10,13,16,19–22:6 6.5070.39 4.2070.17 11.170.28

Otherd 2.62 2.76 1.97

Saturated 39.971.12 36.273.07 45.870.65

Monounsaturated 35.270.48 40.470.88 24.970.92

Unsaturated 57.371.41 60.972.46 50.472.21

n–3 16.270.86 14.071.01 20.771.02

n-6 5.9070.06 5.7170.60 4.7370.51

Sat./Unsat. 0.6670.01 0.6070.07 0.9170.08

aAll ethylenic bonds in the cis configuration;bValues are means7SD of two GC analyses of products from four experiments;cSum of two isomers;dRepresents the unknown components eluted.

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acid and n-3 PUFA, especially EPA and DHA. In view of these results, the Nile perch is apotential nutritional food fish for human consumption.

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