Survey of n-3 and n-6 polyunsaturated fatty acids in fish and fish products

Transcription

1 Strobel et l. Lipids in Helth nd Disese 2012, 11:144 RESEARCH Open Access Survey of n-3 nd n-6 polyunsturted ftty cids in fish nd fish products Cludi Strobel, Gerhrd Jhreis nd Ktrin Kuhnt * Abstrct Bckground: The imblnce of the n-3/n-6 rtio in the Western diet is chrcterised by low intke of n-3 long-chin (LC) PUFA nd concurrent high intke of n-6 PUFA. Fish, in prticulr mrine fish, is unique source of n-3 LC PUFA. However, FA composition of consumed fish chnged, due to the incresing usge of n-6 PUFA-rich vegetble oils in quculture feed nd in fish processing (frying) which both led to further shift in n-6 PUFA to the detriment of n-3 LC PUFA. The im of this study ws to determine the rtio of n-3/n-6 including the contents of EPA nd DHA in fish fillets nd fish products from the Germn mrket (n=123). Furthermore, the study focussed on the FA content in frmed slmon compred to wild slmon s well s in processed Alsk pollock fillet, e.g., fish fingers. Results: Totl ft nd FA content in fish products vried considerbly depending on fish species, feed mngement, nd food processing. Mckerel, herring nd trout fillets chrcteristiclly contined dequte dietry mounts of bsolute EPA nd DHA, due to their high ft contents. However, despite lower ft content, tun, pollock, nd Alsk pollock cn contribute considerble mounts of EPA nd DHA to the humn supply. Frmed slmon re n pproprite source of EPA nd DHA owing to their higher ft content compred to wild slmon (12.3 vs. 2.1 wt %), however with elevted SFA, n-9 nd n-6 FA contents representing the use of vegetble oils nd oilseeds in quculture feed. The n-3/n-6 rtio ws deteriorted (2.9 vs. 12.4) but still cceptble. Compred to pure fish fillets, breded nd pre-fried Alsk pollock fillet contined extrordinrily high ft nd n-6 PUFA levels. Conclusions: Since fish species vry with respect to their n-3 LC PUFA contents, eting vriety of fish is dvisble. High n-6 PUFA contining pre-fried fish support the imblnce of n-3/n-6 rtio in the Western diet. Thus, consumption of pure fish fillets is to be fvoured. The lower n-3 PUFA portion in frmed fish cn be offset by the higher ft content, however, with n unfvourble FA distribution compred to wild fellows. Keywords: Fish, Aqutic food products, n-3 PUFA, n-6 PUFA, Aquculture, Wild slmon, EPA, DHA, Freshwter, Mrine Bckground Fish nd shellfish re considered to be nutritionlly high-qulity food s they re mjor source of mrinederived omeg-3 long-chin polyunsturted ftty cids (n-3 LC PUFA; C 20) for the humn diet [1,2]. In humns, n-3 LC PUFA together with their metbolites (eicosnoids) engged in vrious physiologicl processes nd re essentil for norml growth nd development [3]. They lso ply n importnt role in the prevention of crdiovsculr nd inflmmtory diseses nd hve * Correspondence: ktrin.kuhnt@uni-jen.de Deprtment of Nutritionl Physiology, Institute of Nutrition, Friedrich Schiller University Jen, Dornburger Str. 24, Jen, Germny promising impct on prevention of cognitive decline nd dementi in older people [3-7]. Since n-3 nd n-6 PUFA compete for the sme enzymes for desturtion nd elongtion nd ech clss of PUFA hs different effect on humn helth, n pproprite rtio of both is crucil. In fct, n imblnce is ssocited with the prevlence of vrious chronic diseses [8]. Pst studies indicte tht humn beings evolved on diet with n-6/n-3 rtio of pproximtely 1:1 [9] nd ccording to some uthors, rtio of between 1:1 nd 5:1 is supposedly beneficil to helth [8,10,11]. The current Western diet, involving high consumption of met nd susge products s well s n incresed intke of vegetble oils (vi excessive use in 2012 Strobel et l.; licensee BioMed Centrl Ltd. This is n Open Access rticle distributed under the terms of the Cretive Commons Attribution License ( which permits unrestricted use, distribution, nd reproduction in ny medium, provided the originl work is properly cited.

2 Strobel et l. Lipids in Helth nd Disese 2012, 11:144 Pge 2 of 10 food processing), chrcterises high quntities of n-6 PUFA nd deficit in n-3 PUFA [12,13]. Vegetble oils contin high quntities of n-6 PUFA minly s linoleic cid (C18:2 n-6; LA). The increse in consumption of LA-rich oils (e.g., soyben oil, sunflower oil) is even ssocited with decresed n-3 LC PUFA content in humn body tissue [12]. Current dt revels the n-6/ n-3 rtio in the Western diet s being between 8:1 nd 17:1 [9,14]. Hence, it follows tht by decresing n-6 PUFA nd simultneously incresing n-3 PUFA intke this rtio cn be improved leding to positive effects for humn helth [8,11]. Incresed fish consumption, especilly of mrine origin, cn led to rised supply of n-3 LC PUFA. For this reson, dieticins dvocte eting fish t lest twice week, with preferbly one mel consisting of oily mrine fish such s herring, mckerel or slmon [15]. However, the recommended intke for the mrine-derived LC PUFA eicospentenoic cid (C20:5 n-3; EPA) nd docoshexenoic cid (C22:6 n-3; DHA) s well s for totl intke of n-3 PUFA vries between the different scientific pnels. Recommendtions for totl EPA nd DHA re between 200 mg/d nd 500 mg/d [16,17]. The estimted current intke in the Europen popultion vries between 80 mg/d to 420 mg/d [16]. Since fish nd mmmls lck Δ12 nd Δ15 desturses responsible for converting oleic cid (18:1 n-9; OA) into LA nd α-linolenic cid (18:3 n-3; ALA), they re unble to synthesize n-3 LC PUFA de novo from precursors nd dietry intke of LA nd ALA is essentil [18,19]. In both fish nd humns, n-3 LC PUFA supply principlly depends on the diet nd on the bility to elongte nd desturte plnt-derived ALA to their longer C 20 nd C 22 homologues such s EPA nd DHA [20,21]. The bsic FA composition which is cumultive in the mrine food chin depends on the primry producers such s mrine phytoplnkton (microlge like ditome) [18,22]. These primry mrine producers cn effectively synthesize LC PUFA from ALA nd LA vi series of desturtion nd elongtion rections. Finlly, they re ble to directly synthesis DHA from docospentenoic cid (C22:5 n-3; DPA) vi Δ4 desturtion [22-24]. Interestingly, some microbes use polyketide synthse-like rection to produce PUFA [22,24,25]. Wheres the mrine food chin is rich in EPA nd DHA, the freshwter food system contins higher levels of LA nd ALA [19,26] leding to obvious differences between freshwter nd mrine fish in terms of FA distribution. However, some freshwter fish species cn lso serve s vluble source of EPA nd DHA [27-29], which they derive from freshwter plnkton [30] nd by endogenous metbolism [19]. Due to the high globl demnds for fish nd the resulting overfishing of the ses ( fishing down mrine/or qutic food webs [31,32,33], mrine nd freshwter quculture hs tken on incresing importnce. For exmple, frming nd consumption of slmonids hs drmticlly incresed during the pst 20 yers [33]. Furthermore, some species of freshwter fish re becoming incresingly populr mongst consumers nd re hevily cultivted. One exmple is the iridescent shrk (Pngsius hypophthlmus). It ws one of the most frequently consumed fish species in Germny in 2009 [34]. The diet of wild fish is very different from tht of their fellow species in quculture. In fct, quculture of finfish nd crustcens is still highly dependent upon mrine cpture fisheries tht provide key dietry nutrients, such s fish mel nd fish oil [35]. Fish oil is the primry source of n-3 LC PUFA in quculture [33,36,37]. Since, mrine fish oils comprise limiting fctor for the strongly growing fish frming industry (5-10% per nnum; [38]) quculture diets contin wide vriety of lterntive plnt-bsed ingredients such s legume seeds, oilseed ckes, lef mels nd n incresing portion of vegetble oils [36,39]. However, replcing fish oils with vegetble oils mens tht less n-3 LC PUFA re vilble in the fish diet, lthough in some oils such s flxseed oil, quntity of ALA is present nd cn be converted only to limited extent into LC metbolites in fish. In generl, vegetble oils in fish feed cn hve detrimentl effect on the FA distribution in fish s they cn lter the n-3/n-6 rtio [18]. In view of the fct tht demnd for fish is globlly incresing nd tht fish consumption is lso generlly recommended by dieticins, surprisingly, current overview of FA profiles nd FA content in different fish species nd in food products derived from mrine nd freshwter fish is lcking in the literture. Therefore, the im of this work ws to nlyse FA distribution (prticulrly n-3 nd n-6 PUFA) in vrious fish products nd in fillets of frequently consumed fish species vilble on the Germn mrket. Moreover, focus ws dditionlly plced on nlysing the FA content in frmed compred to wild slmon s well s in processed Alsk pollock fillet (e.g. fish fingers). Results Totl ft nd ftty cids in vrious fish products nd fish species Totl ft content of fresh weight of ll nlysed smples vried between 0.39% (monkfish fillet) nd 40.4% (cod liver; Tble 1). The totl n-3 PUFA proportion rnged from 2.96 ± 0.61% of FAME (iridescent shrk) to 51.2 ± 3.69% of FAME (cod fillet) (Tble 1). The lrgest frction of n-3 PUFA constituted DHA, EPA nd ALA, while DHA ws generlly higher in contrst to EPA (Tble 2). Compring the FA proportions of the seven most frequently consumed fish fillet types in Germny showed

3 Strobel et l. Lipids in Helth nd Disese 2012, 11:144 Pge 3 of 10 Tble 1 Totl ft, n-3 nd n-6 PUFA contents of different fish species Totl ft P EPA & DHA P n-3 PUFA P n-6 PUFA Fish species [wt %] [% of FAME] [wt %] [% of FAME] [wt %] [% of FAME] [wt %] (lphbeticl order) Men ± SD Men ± SD Men ± SD Men ± SD Men ± SD Men ± SD Men ± SD Alsk pollock 1 (n=17) 3.71 ± ± ± ± ± ± ± 1.96 Anchovies 2 (n=1) Blck hlibut, smoked (n=1) Butterfish, smoked (n=1) Ctfish, cnned fish (n=1) Cod fillet (n=3) 0.56 ± ± ± ± ± ± ± 0.02 Cod liver (n=1) Cod, smoked (n=1) Eel, smoked (n=1) Fried clmri 3 (n=2) 9.45 ± ± ± ± ± ± ± 2.05 Herring (n=9) 12.7 ± ± ± ± ± ± ± 0.10 Iridescent shrk (n=10) 1.54 ± ± ± ± ± ± ± 0.06 Louisin-cryfish (n=1) Mckerel (n=3) 20.6 ± ± ± ± ± ± ± 0.26 Monkfish (n=1) New Zelnd hke (n=1) Plice (n=1) Pollock (n=10) 0.99 ± ± ± ± ± ± ± 0.02 Prwn (n=4) 0.53 ± ± ± ± ± ± ± 0.04 Redfish, fillet (n=1) Redfish, smoked (n=1) Slmon; frmed (n=11) 12.3 ± ± ± ± ± ± ± 1.07 Slmon; wild (n=10) 2.07 ± ± ± ± ± ± ± 0.03 Srdine 4 (n=2) 10.2 ± ± ± ± ± ± ± 2.13 Spined loch, fillet (n=1) Spiny dogfish 5 (n=2) 33.8 ± ± ± ± ± ± ± 0.56 Sprt, smoked (n=2) 17.9 ± ± ± ± ± ± ± 0.59 Tilpi (n=1) Trout (n=10) 7.93 ± ± ± ± ± ± ± 0.60 Tun (n=10) 2.28 ± ± ± ± ± ± ± 0.08 Victori perch, fillet (n=1) Whitefish, smoked (n=1) Znder fillet (n=1) including fish fingers with coting, pure fillets nd fillets with removed coting, 2 in tin with oil (drined), 3 in crispy coting, 4 in tin with oil (drined), 5 curled strips of smoked dogfish; wt %, % of fresh weight. tht pollock fillets contined the highest portion of EPA nd DHA (44.3% of FAME), wheres iridescent shrk once more contined the lowest levels (1.66% of FAME; Tble 2). The totl ft content is prticulrly importnt for FA concentrtion with respect to the fresh weight. Iridescent shrk lso hd the lest bsolute n-3 PUFA content (0.04 ± 0.02 wt %). Fillets of herring, rinbow trout, nd slmon (verge of wild nd frmed) showed the highest bsolute contents of EPA nd DHA relted to high ft content (Tble 2). Comprison of wild nd frmed slmon Fillets from wild nd frmed slmon differed with regrd to ft content nd FA distribution (Tble 3). Ft content in fillets from cultured slmon ws significntly higher thn from the wild counterprt (12.3 vs wt %). In

4 Strobel et l. Lipids in Helth nd Disese 2012, 11:144 Pge 4 of 10 Tble 2 Totl ft content nd FA proportion of fillets of the seven most frequently consumed fish species Mrine Freshwter/mrine Freshwter (Aquculture) Herring 1 Tun 2 Pollock 3 Alsk pollock 4 Slmon 5 Rinbow trout 6 Iridescent shrk 7 (n = 9) (n = 10) (n = 10) (n = 10) (n = 21) (n = 10) (n = 10) Men ± SD Men ± SD Men ± SD Men ± SD Men ± SD Men ± SD Men ± SD Totl ft [wt %] 12.7 ± ± 2.59 c 0.99 ± 0.37 c 0.81 ± 0.27 c 7.43 ± 6.25 b 7.93 ± 3.79 b 1.54 ± 0.49 c FA [% of FAME] C16: ± 1.35 f 22.3 ± 2.79 b 18.9 ± 1.72 c 17.7 ± 2.48 cd 15.0 ± 2.98 ef 16.0 ± 1.64 de 28.9 ± 2.00 C18: ± 0.12 d 8.15 ± ± 0.85 b 3.09 ± 0.35 c 2.92 ± 0.56 c 3.42 ± 0.53 c 8.20 ± 0.76 C18:1 n-9 (OA) 10.1 ± 3.86 d 11.5 ± 1.93 d 9.67 ± 2.81 d 13.1 ± 4.78 d 18.1 ± 7.65 c 23.9 ± 3.82 b 37.4 ± 1.03 P n-3 PUFA 16.1 ± 2.69 d 35.1 ± 4.84 b 46.8 ± ± 8.65 b 24.9 ± 7.74 c 21.9 ± 4.38 c 2.96 ± 0.61 e C18:3 n-3 (ALA) 1.08 ± 0.16 bc 0.29 ± 0.13 c 0.43 ± 0.10 c 0.73 ± 0.54 c 1.47 ± 1.20 b 1.91 ± ± 0.42 c C18:4 n-3 (SDA) 1.93 ± ± 0.32 de 0.49 ± 0.19 cd 0.35 ± 0.10 de 1.04 ± 0.40 b 0.78 ± 0.34 bc 0.04 ± 0.02 e C20:4 n ± 0.12 c 0.26 ± 0.16 c 0.45 ± 0.11 c 0.28 ± 0.08 c 0.99 ± ± 0.17 b 0.05 ± 0.01 d C20:5 n-3 (EPA) 5.21 ± 1.10 cd 4.42 ± 1.37 d 9.82 ± 1.66 b 14.5 ± ± 2.18 c 4.07 ± 1.31 d 0.22 ± 0.05 e C22:5 n-3 (DPA) 0.53 ± 0.09 cd 0.87 ± 0.41 cd 0.91 ± 0.25 cd 1.04 ± 0.29 c 2.38 ± ± 0.44 b 0.31 ± 0.04 d C22:6 n-3 (DHA) 6.83 ± 1.44 e 28.4 ± 4.92 b 34.5 ± ± 5.27 c 12.3 ± 6.44 d 12.5 ± 3.58 d 1.44 ± 0.41 f P EPA & DHA 12.0 ± 2.10 d 32.9 ± 5.18 b 44.3 ± ± 8.57 b 18.7 ± 8.08 c 16.6 ± 4.44 cd 1.66 ± 0.45 e P n-6 PUFA 2.58 ± 0.41 b 7.67 ± 1.70 b 4.27 ± 2.37 b 12.6 ± ± 6.09 b 12.2 ± ± 2.16 C18:2 n-6 (LA) 1.90 ± 0.50 c 1.25 ± 0.25 c 2.15 ± 2.51 c 11.4 ± ± 5.77 bc 10.3 ± 3.97 b 8.15 ± 1.88 b C18:3 n-6 (GLA) 0.11 ± 0.03 b 0.14 ± 0.04 b 0.09 ± 0.02 b 0.11 ± 0.03 b 0.23 ± ± ± 0.05 C20:4 n-6 (AA) 0.21 ± 0.03 d 3.38 ± ± 0.20 b 0.73 ± 0.17 c 0.40 ± 0.12 cd 0.49 ± 0.16 cd 1.56 ± 0.45 b C22:5 n ± 0.03 c 2.50 ± ± 0.07 c 0.16 ± 0.04 c 0.16 ± 0.04 c 0.22 ± 0.11 c 0.82 ± 0.24 b P P n-3/ n ± 1.70 bc 4.97 ± 2.17 bc 12.6 ± ± 8.53 b 7.41 ± 5.68 b 2.06 ± 0.91 c 0.24 ± 0.03 d P P n-6/ n ± 0.04 c 0.22 ± 0.06 c 0.09 ± 0.06 c 0.38 ± 0.35 bc 0.34 ± 0.39 bc 0.62 ± 0.39 b 4.19 ± 0.58 P SFA 23.2 ± 2.30 c 34.8 ± 4.00 b 25.9 ± 2.08 c 22.7 ± 2.67 c 23.2 ± 3.87 c 24.2 ± 2.32 c 41.3 ± 2.81 P MUFA 53.4 ± ± 4.21 c 20.7 ± 4.77 c 22.9 ± 3.80 c 41.0 ± 7.19 b 37.9 ± 3.89 b 40.9 ± 1.13 b P PUFA 20.0 ± 2.65 d 43.2 ± 5.06 b 51.3 ± ± ± 6.92 c 35.2 ± 2.07 c 15.3 ± 2.66 e FA [wt %] P n-3 PUFA 1.95 ± ± 0.92 b 0.43 ± 0.15 b 0.30 ± 0.11 b 1.51 ± ± ± 0.02 b C18:3 n-3 (ALA) 0.13 ± 0.04 b 0.01 ± 0.01 b 0.01 ± 0.00 b 0.01 ± 0.01 b 0.15 ± ± ± 0.01 b C20:5 n-3 (EPA) 0.64 ± ± 0.20 cd 0.09 ± 0.04 cd 0.11 ± 0.04 cd 0.41 ± 0.32 b 0.30 ± 0.20 bc 0.01 ± 0.00 d C22:6 n-3 (DHA) 0.81 ± ± 0.63 b 0.32 ± 0.11 bc 0.17 ± 0.06 c 0.61 ± 0.37 b 0.86 ± ± 0.01 c P n-6 PUFA 0.31 ± 0.10 b 0.14 ± 0.08 b 0.04 ± 0.02 b 0.10 ± 0.10 b 0.71 ± 1.00 b 0.94 ± ± 0.06 b C18:2 n-6 (LA) 0.23 ± 0.09 b 0.03 ± 0.04 b 0.02 ± 0.02 b 0.10 ± 0.10 b 0.59 ± 0.90 b 0.80 ± ± 0.04 b C20:4 n-6 (AA) 0.03 ± 0.01 bcd 0.05 ± ± 0.01 cd 0.01 ± 0.00 d 0.03 ± 0.02 bc 0.04 ± 0.02 b 0.02 ± 0.01 bcd 1 contins herring fillets (Clupe hrengus) in tin (drined); 2 consists of Thunnus lbcres, Thunnus Allung, Ktsuwonus pelmis; 3 Pollchius virens; 4 Thergr chlcogrmm, consists of pure fillets nd fillets with removed coting; 5 consists of wild slmon (Oncorhynchus ket, Oncorhynchus gorbusch, Oncorhynchus nerk) nd slmon from quculture (Slmo slr); 6 Oncorhynchus mykiss; 7 Pngsius hypophthlmus. bc Mens with different superscript letters indicte significnt differences, P AA, rchidonic cid; ALA, α-linolenic cid; DHA, docoshexenoic cid; DPA, docospentenoic cid; EPA, eicospentenoic cid; GLA, γ-linolenic cid; LA, linoleic cid; OA, oleic cid; SDA, steridonic cid. terms of FAME, wild slmon showed significntly higher proportion of totl n-3 PUFA (28.9% vs. 21.2%), which resulted minly from higher EPA (7.29%) nd DHA (16.9% of FAME; Tble 3). In contrst, cultured slmon exhibited greter bsolute mounts of totl n-3 PUFA, which were, however, ssocited with higher ft intke consisting minly of SFA, OA nd LA (Tble 3). Comprison of breded nd pure Alsk pollock fillet Fish fingers contined significntly higher totl ft nd n-6 PUFA compred to pure Alsk pollock fillets (Tble 4). In ddition, the breded pre-fried products hd incresed MUFA (minly OA) nd SFA levels in reltion to ft. Although Alsk pollock fish fingers with removed breding showed significntly lower n-6 PUFA (19.0% of FAME) in

5 Strobel et l. Lipids in Helth nd Disese 2012, 11:144 Pge 5 of 10 Tble 3 Totl ft nd FA proportion of wild nd frmed slmon Slmon fillet Slmon fillet Reltive FA mount [% of FAME] Absolute FA mount [% of fresh weight] Wild 1 Frmed 2 Wild Frmed (n = 10) (n = 11) (n = 10) (n = 11) Men ± SD Men ± SD P 3 Men ± SD Men ± SD P 4 Totl Ft [wt %] 2.07 ± ± 4.72* FA C16: ± ± 1.85* 0.32 ± ± 0.60* C18: ± ± ± ± 0.17* C18:1 n-9 (OA) 13.4 ± ± 8.42* 0.27 ± ± 1.83* P n-3 PUFA 28.9 ± ± 4.03* 0.53 ± ± 0.78* C18:3 n-3 (ALA) 0.58 ± ± 1.15* 0.01 ± ± 0.20* C18:4 n-3 (SDA) 0.94 ± ± ± ± 0.05* C20:4 n ± ± 0.35* 0.02 ± ± 0.05* C20:5 n-3 (EPA) 7.29 ± ± ± ± 0.26* C22:5 n-3 (DPA) 2.21 ± ± ± ± 0.12* C22:6 n-3 (DHA) 16.9 ± ± 2.67* 0.31 ± ± 0.29* P EPA & DHA 24.2 ± ± 3.92* 0.44 ± ± 0.52* P n-6 PUFA 2.35 ± ± 6.23* 0.05 ± ± 1.07* C18:2 n-6 (LA) 1.27 ± ± 6.04* 0.02 ± ± 1.00* C18:3 n-6 (GLA) 0.14 ± ± 0.10* 0.01 ± ± 0.02* C20:4 n-6 (AA) 0.40 ± ± ± ± 0.02* C22:5 n ± ± ± ± 0.01* P P n-3/ n ± ± 1.96* 12.4 ± ± 1.96* P n-6/ P n ± ± 0.42* 0.09 ± ± 0.42* P SFA 24.7 ± ± ± ± 0.95* P MUFA 39.5 ± ± ± ± 2.22* P PUFA 32.0 ± ± ± ± 1.56* 1 Wild slmon (Oncorhynchus ket, Oncorhynchus gorbusch, Oncorhynchus nerk); 2 slmon from quculture (Slmo slr), 3 significnt differences between wild nd quculture slmon in terms of % of FAME, P 0.05; 4 significnt differences between wild nd quculture slmon in terms of % of fresh weight, P AA, rchidonic cid; ALA, α-linolenic cid; DHA, docoshexenoic cid; DPA, docospentenoic cid; EPA, eicospentenoic cid; GLA, γ-linolenic cid; LA, linoleic cid; OA, oleic cid; SDA, steridonic cid. contrst to the breded products (51.5% of FAME), these concentrtions were still higher in comprison to pure fillets (2.6% of FAME). The n-3 PUFA portion ws the lowest in fish fingers, but with reference to the higher ft content, the bsolute n-3 PUFA per 100 g product ws nlogous (0.39, 0.30, 0.30 wt %). However, when seprted into single n-3 PUFA, it is evident tht EPA nd DHA in fish fingers showed significntly the lowest levels (Tble 4) in ccordnce with the decresed fish portion per 100 g of fish fingers (Tble 4). Discussion Totl ft nd n-3 PUFA in vrious fish products nd fish fillets The totl ft content nd the proportion of n-3 PUFA vried gretly mongst the fish species nd the fish products. It is not surprising tht due to their incresed bsolute EPA nd DHA levels, oily se fish such s mckerel nd herring re considered to be of higher nutritionl vlue (Tbles 1, 2). In order to meet dietry EPA nd DHA recommendtions in humn nutrition the Americn Hert Assocition (AHA) recommends the consumption of two servings (3 oz; 85 g) of fish (prticulrly oily fish) twice week [40]. Referring to the ft content, the Germn Nutrition Society (DGE) recommends lower serving of oily fish (e.g., 70 g) nd greter serving of len fish ( g) once week [41]. This illustrtes the importnce of nlysing the totl ft nd its reltion to the bsolute FA content in fish species. Nonetheless, ccording to the dt obtined in this study, we cn sfely ssume tht, even the other fish species frequently consumed in Germny re dequte

6 Strobel et l. Lipids in Helth nd Disese 2012, 11:144 Pge 6 of 10 Tble 4 Totl ft content, FA proportion nd FA content of Alsk pollock 1 products depending on breding Reltive FA mount [% of FAME] Absolute FA mount [% of fresh weight] Pure fillets Fish fingers with removed coting Fish fingers with coting Pure fillets Fish fingers with removed coting Fish fingers with coting (n = 4) (n = 6) (n = 7) (n = 4) (n = 6) (n = 7) Men ± SD Men ± SD Men ± SD Men ± SD Men ± SD Men ± SD Totl ft [wt %] 0.77 ± 0.31 b 0.88 ± 0.26 b 7.85 ± 1.61 FA C16: ± ± 0.83 b 7.48 ± 1.75 c 0.16 ± 0.01 b 0.14 ± 0.01 b 0.59 ± 0.14 C18: ± ± 0.31 b 3.36 ± ± 0.00 b 0.03 ± 0.00 b 0.26 ± 0.03 C18:1 n-9 (OA) 6.81 ± 0.46 c 16.5 ± 1.79 b 29.6 ± ± 0.00 c 0.15 ± 0.02 b 2.32 ± 0.58 P n-3 PUFA 50.2 ± ± 4.13 b 3.83 ± 1.60 c 0.39 ± ± ± 0.13 C18:3 n-3 (ALA) 0.29 ± 0.08 c 0.94 ± 0.59 b 1.69 ± ± 0.00 b 0.01 ± 0.01 b 0.13 ± 0.12 C18:4 n-3 (SDA) 0.43 ± ± 0.08 b 0.02 ± 0.01 c 0.00 ± ± ± 0.00 C20:4 n ± ± 0.05 b 0.01 ± 0.01 c 0.00 ± ± ± 0.00 C20:5 n-3 (EPA) 18.4 ± ± 1.61 b 0.82 ± 0.16 c 0.14 ± ± ± 0.01 b C22:5 n-3 (DPA) 1.26 ± ± 0.27 b 0.07 ± 0.01 c 0.01 ± ± ± 0.00 C22:6 n-3 (DHA) 29.4 ± ± 2.45 b 1.20 ± 0.25 c 0.23 ± ± ± 0.02 b P EPA & DHA 47.8 ± ± 4.02 b 2.02 ± 0.40 c 0.37 ± ± ± 0.03 b P n-6 PUFA 2.58 ± 0.43 c 19.0 ± 6.85 b 51.5 ± ± 0.00 b 0.17 ± 0.06 b 4.04 ± 0.60 C18:2 n-6 (LA) 1.07 ± 0.46 c 18.0 ± 6.90 b 51.4 ± ± 0.00 b 0.16 ± 0.06 b 4.03 ± 0.60 C18:3 n-6 (GLA) 0.13 ± ± 0.03 b 0.01 ± 0.01 c 0.00 ± ± ± 0.00 C20:4 n-6 (AA) 0.96 ± ± 0.05 b 0.04 ± 0.01 c 0.01 ± ± ± 0.00 b C22:5 n ± ± 0.02 b 0.01 ± 0.01 c 0.00 ± ± ± 0.00 P P n-3/ n ± ± 1.48 b 0.08 ± 0.04 c 19.8 ± ± 1.48 b 0.08 ± 0.04 c P P n-6/ n ± 0.01 c 0.59 ± 0.28 b 16.0 ± ± 0.01 c 0.59 ± 0.28 b 16.0 ± 7.67 P SFA 26.0 ± ± 0.69 b 12.2 ± 1.87 c 0.20 ± 0.01 b 0.18 ± 0.01 b 0.96 ± 0.15 P MUFA 18.4 ± 0.34 b 24.9 ± 3.00 b 31.7 ± ± 0.00 b 0.22 ± 0.03 b 2.49 ± 0.62 b P PUFA 53.2 ± ± ± ± 0.01 b 0.47 ± 0.03 b 4.36 ± Thergr chlcogrmm. bc Mens with different superscript letters indicte significnt differences, P 0.05; P 0.1 compred to pure fillets. AA, rchidonic cid; ALA, α-linolenic cid; DHA, docoshexenoic cid; DPA, docospentenoic cid; EPA, eicospentenoic cid; GLA, γ-linolenic cid; LA, linoleic cid; OA, oleic cid; SDA, steridonic cid. sources of n-3 LC PUFA (Tble 2). In contrst, the incresingly consumed iridescent shrk nd tilpi fils to sufficiently contribute towrds n-3 PUFA supply in humns (Tbles 1, 2). In generl, ft nd FA content in fish vry gretly both between nd within fish species s vlues re minly influenced by feeding s well s further fctors such s the geogrphicl loction of the fishing ground, seson, food vilbility, wter temperture, ge nd size of the fish nd the mturtion sttus [42-47]. This cn be seen in the fct tht published dt vries to gret extent with respect to FA content in fish. In ddition, it is well known tht lipid distribution in fish is not uniform nd fluctutes throughout the body [44,48]. In cod, for exmple, reserve ft is stored in the liver [49] nd not between the muscle fibrils s in oily fish, rendering cod fillet very len (in liver the ft content is 67 times higher compred to fillet; Tble 1). Therefore, despite cod fillets contining significntly higher n-3 PUFA (51.2 ± 3.7% of FAME) thn cod liver (22.0% of FAME) but the bsolute n-3 PUFA content ws low (0.28% vs. 8.5%; Tble 1). Differences in FA profile nd FA contents between wild nd frmed fish Wild slmon is lso known s Pcific slmon [44]. The reltively high n-3 PUFA nd low n-6 PUFA proportion found in wild slmon is directly relted to their diet. Wild slmon re predtory fish tht feed on smller fish, e.g. herring, sprt or shellfish, which contin elevted n-3 LC PUFA. Slmon nd trout re mjor cultivted species rised on compound quculture feeds [35]. The bulk of Atlntic slmon (Slmo slr) vilble on the mrket tody is frmed. The feed for frmed slmon is bsed on fish mel nd fish oil rich in n-3 LC PUFA [36]. Therefore, frmed fish should hve similr n-3 PUFA levels comprble to

7 Strobel et l. Lipids in Helth nd Disese 2012, 11:144 Pge 7 of 10 wild fish [44]. However, becuse mrine fish oils re limiting fctor, vegetble oils nd oil seeds re frequent lterntives in quculture feed [35-37,50] nd led to high mounts of n-9 MUFA nd n-6 PUFA s seen in frmed slmon (Tble 3). Recent studies hve confirmed n increse of C 18 FA such s OA, LA, nd ALA in the fillet of frmed fish through the use of vegetble oils in the feed, whilst the content of n-3 LC PUFA ws decresed [36,51-54]. The ctul noticebly higher LA nd ALA found in cultured slmon nd lso in rinbow trout (Oncorhynchus mykiss; often clled slmon-trout) presumbly indictes the use of vegetble oils such s sunflower, soyben, rpeseed, nd linseed oil in the feed (Tbles 2, 3). Rinbow trout on the mrket originte minly from quculture [35]. The reltively high EPA nd DHA levels in frmed slmon nd rinbow trout (13.7% nd 16.6% of FAME; Tbles 2, 3) cn result primrily from the direct dietry intke of fish oil-contining feed [55], but lso to lesser extent from the limited endogenous conversion of ALA [19,56]. Turkey wild rinbow trout flesh contined similr mounts of totl n-3 PUFA compred to cultured rinbow trout, however, with higher ALA nd EPA nd lower DHA [48]. In contrst, iridescent shrk, which re lso lmost exclusively frmed, hve only low n-3 PUFA level (Tble 2). Industril feed for iridescent shrk (rice hulls, rice, soy flour, nd bnns [57-59]) hs reltively low concentrtion of n-3 PUFA nd cn contin round 2-3% fish oil [57]. This hs only low impct on n-3 PUFA content s reflected by recent nlyses. The minly plnt-bsed nutrition is echoed in higher n-6 PUFA proportion, however, it is negligible with respect to the low ft content in fresh weight (Tble 2). The high levels of ft in the feed for frmed slmon re intended to chieve stronger growth s well s fster lipid deposition within short period of time. In most cultured fish, the often lower n-3 PUFA portion is offset by higher ft content [44,60]. Therefore, the bsolute EPA nd DHA intke when consuming 100 g of frmed slmon would be 3 4 times higher compred to eting wild slmon (Tble 3), thus, identifying frmed slmon s suitble source of n-3 LC PUFA. Although frmed slmon hs n dequte n-3/n-6 rtio (2.9), it is lower compred to wild slmon (12.4) nd consumption is ccompnied by high intke of totl ft (e.g., 5 times higher SFA content). According to the present results, totl ft ws lso higher in cultured compred to wild rinbow trout [48]. Whilst the flesh contined similr mounts, the skin of the cultured fish hd higher lipid content [48]. In generl, quculture feeding shows regionl disprities nd feed cn contin different lipid sources nd concentrtions of fish oil [39]. All in ll, the conditions in quculture feeding re extremely heterogeneous [35] nd cn chnge rpidly with trend to further chnge in the future. The precise composition of the different feeds of ll the vrious fish smples nlysed ws not known, in this survey, hence no direct conclusions relting to the influence of ftty cid composition between the diets of the nlysed wild nd frmed slmon is possible. Moreover, we nlysed only smples from the Germn mrket which dditionlly differ with regrd to species, diet (piscivorous, plnkton consuming, vrious quculture feed), fishing zone nd individul genetic vrition. Clerly, this survey is limited to the nlysed smples nd is not representtive of ll frmed or wild slmon. Nevertheless, the present dt cn provide n indiction tht wild slmon hve generlly lower ft nd n-6 PUFA content, resulting in fvourble n-3/n-6 rtio compred to fellow frmed species. However, due to the stedily incresing world humn popultion together with the depleting supply of mrine fish due to overfishing of the ses, obtining the dietry recommend dose of n-3 LC PUFA vi consumption of wild fish is not vible solution in the long term. Frmed fish cn generlly be regrded s n pproprite source of EPA nd DHA with respect to the higher ft content which is clerly dependent on EPA nd DHA contined quculture feed [38]. Feeding only n-3 PUFA-poor vegetble oils such s soyben nd plm oil s lipid source will led to decline of EPA nd DHA in frmed fish with n increse of SFA nd n-6 PUFA. Thus, bsed on this trend, fish consumption in the future will lose its unique positive helth impct. Therefore, number of promising strtegies relted ltering quculture diets with respect to providing dequte lterntives to fishmel nd fish oil re being developed nd implemented in order to improve the nutritionl vlue of commercilly frmed fish in the future; e.g., culture of qutic (prtly trnsgenic) microbes (microlge nd yest) which synthesize EPA nd/or DHA nd trnsgenic plnts (e.g., rpeseed) which produce these n-3 LC PUFA [18,23,24,38,61,62]. Influence of food processing on FA contents using the exmple of fish fingers The processing of fish fillets (breding nd frying in vegetble oils) hd n dverse influence on totl ft nd FA distribution, especilly on incresing LA nd decresing the n-3/n-6 rtio (0.08 vs vs. 19.8; Tble 4). Due to the lower proportion of pure fish fillet in 100 g fish finger (t lest 65% fillet), the EPA nd DHA concentrtions were hlved, whilst ALA, OA, nd LA hd incresed due to breding nd frying (Tble 4). The totl n-6 PUFA intke is certinly higher in breded fish foods compred to frmed slmon fillet s confirmed in the

8 Strobel et l. Lipids in Helth nd Disese 2012, 11:144 Pge 8 of 10 present nlysis (4.0 vs. 1.3 wt %). Furthermore, removing the breding gretly reduced the high ft content in fish fingers, lthough, due to frying oils penetrting into the fish fillet, the n-6 lipid portion ws still higher (Tble 4). Similrly, the totl ft content ws incresed in breded cod fillet whilst the n-3/n-6 rtio decresed [63]. In generl, the totl trns-fa (nlysed by GC-column: CP-select for FAME; 200 m) were t lest below 2% of FAME (dt not shown). Conclusion It cn be concluded tht the n-3 PUFA content of foods of qutic origin vries strongly depending on the fish species, the ft content of fish, nd the feeding conditions. Consumption of fish nd shellfish does not necessrily result in sufficient supply of EPA nd DHA in humns. Therefore, consumers should consume vriety of different fish species. The present work confirmed tht intke of the frequently consumed fish species such s herring, tun, pollock, Alsk pollock, slmon, nd rinbow trout meets the dietry recommendtions for totl EPA nd DHA of mg/d. Due to their generlly higher ft content, even frmed fish cn be n pproprite source of EPA nd DHA, lthough these re ssocited with higher mounts of n-6 PUFA nd lower n-3/n-6 rtio compred to wild fish. One reson for this low rtio is the incresing usge of n-6 PUFA-rich vegetble oils s n lterntive to fish oil in quculture feed, resulting in decresed nutritionl vlue of frmed fish. In generl, strtegies to ensure lterntive n-3 LC PUFA sources in quculture feed need to be developed nd relised (e.g., trnsgenic microlge nd plnts). Consumption of breded pre-fried fish should generlly be voided owing to the high ft nd n-6 PUFA content which is known to promote the shift to n unfvourble n-3/n-6 rtio, currently widespred phenomenon of the n-6 PUFA-rich Western diet. Mterils nd methods Smples The fresh, cnned or deep-frozen pckged fish smples (n = 123; 26 fish species nd shellfish) used for the study were purchsed in vrious Germn discounters, supermrkets nd fish counters between 2009 nd For cnned fish, suces nd oils were seprted from the fish fillet. Fish fingers mde of Alsk pollock (Thergr chlcogrmm) were nlysed both with nd without breded coting. To determine the most frequently consumed fish species, dt of fish consumption from internl studies (unpublished dt) nd other references (e.g., [34]) were used. The group of wild slmon comprised Oncorhynchus ket, Oncorhynchus gorbusch nd Oncorhynchus nerk wheres the quculture slmon group consisted of Slmo slr. Dt from fish smples in Tbles 2 nd 3 re exclusively from fillets (skin nd bones hd been removed). Smple preprtion Smples were stored t 20 C until prepred for lyophilistion. Following lyophilistion, smples were crushed, homogenised, nd stored t 20 C until further nlysis. After n cid hydrolysis using 4 N hydrochloric cid (Crl Roth GmbH & Co. KG, Krlsruhe, Germny), totl ft content ws extrcted in SOXTHERM 2000 S306 Automtic Extrctor System Gerhrdt (Gerhrdt; Bonn, Germny) with 140 ml of petroleum ether (Crl Roth GmbH & Co. KG; extrction time: 30 min; temperture: 150 C). The mount of totl ft expressed s % (g/100 g) of fresh weight (wt %) ws determined grvimetriclly fter drying. Lipids for FA nlysis were extrcted ccording to Folch et l. [64] (methnol/chloroform/2% sodium chloride solution; 1/2/1 v/v/v; Merck KGA, Drmstdt, Germny). To prevent oxidtion of the sensitive n-3 nd n-6 PUFA during smple processing, methnol incorporting the ntioxidnt 2,6-di-tert-butyl-4-methylphenol (BHT; 0.05%; Fluk Chemie AG, Buchs, Switzerlnd) ws employed. We hd previously verified tht possible BHT peks would not disturb the gs chromtogrphy (GC) nlysis [unpublished results]. The lipid extrct ws stored t 20 C until further nlysis. Totl lipids (25 mg) were sponified with 0.5 M methnolic sodium hydroxide solution t 100 C (10 min). The subsequent methyltion of FA to FA methyl esters (FAME) ws performed using methnolic boron trifluoride (BF 3 ) solution (10% w/w, Supelco; Tufkirchen, Germny) t 100 C for 5 min [65]. The efficiency of methyltion ws proved by thin-lyer chromtogrphy. GC nlysis The FAME were nlysed by GC (GC-17A; Shimdzu, Kyoto, Jpn) using 60 m fused-silic cpillry column of medium polrity (DB 225MS: 60 m 0.25 mm i.d. with 0.25 mm film thickness; Agilent Technologies, USA). Conditions for GC nlysis nd pek integrtion s well s the stndrds used hve previously been described by Kuhnt et l. [66]. In totl, 86 FA were identified with minimum re of 500 counts (2% FAME in hexne, split rtio 1:100). To identify fish oil specific peks, we used in ddition to stndrds (No. 463, 674: NU-CHEK PREP, INC., Elysin, U.S.; BR2, BR4, ME 93: Lrodn, Mlmö, Sweden; Supelco W 37 Component FAME Mix: Supelco, Bellefonte, U.S. [66]) commercil menhden oil (PUFA-3: Mtrey LLC, USA). Only identified peks were included in the summtion of the pek

9 Strobel et l. Lipids in Helth nd Disese 2012, 11:144 Pge 9 of 10 res. FA were expressed s FAME of totl identified FAME (FA/% of totl FAME). To convert FAME into bsolute FA content in totl ft extrcts, we used the fctor 0.9 to consider the portion of glycerine (FA/% of fresh weight; wt %). The FAME were grouped into sturted FA (SFA), monounsturted FA (MUFA), PUFA, nd LC PUFA (C 20). Totl n-3 nd n-6 PUFA were clculted without conjugted linoleic cids. Sttisticl nlysis Sttisticl nlysis ws crried out using PASW Sttistics, version 18.0 ( 2009 SPSS Sttistics 18 Inc, Illinois, USA). Results were stted s mens with stndrd devition (SD) nd P 0.05 indicted significnt difference. The single-fctor ANOVA ws used for compring the men vlue between two groups, whilst the multivrite post hoc test ccording to Student-Newmn-Keuls ws employed to compre the men vlues of severl food groups. Abbrevitions AA: Archidonic cid; ALA: α-linolenic cid; BF 3 : Boron trifluoride; BHT: 2,6-ditert-butyl-4-methylphenol; DHA: Docoshexenoic cid; DPA: Docospentenoic cid; EPA: Eicospentenoic cid; FA: Ftty cids; FAME: Ftty cid methyl esters; GC: Gs chromtogrphy; GLA: γ-linolenic cid; LA: Linoleic cid; LC PUFA: Long chin polyunsturted ftty cids; MUFA: Monounsturted ftty cids; OA: Oleic cid; PUFA: Polyunsturted ftty cids; SDA: Steridonic cid; SFA: Sturted ftty cids. Competing interests The uthors declre tht they hve no competing interests. Authors contributions KK nd GJ designed the study. CS nd KK collected the smples, performed the ftty cid nlysis nd the sttisticl nlyses. CS nd KK wrote the pper. All uthors red nd pproved the finl mnuscript. Acknowledgements The study ws supported by the Germn Reserch Foundtion, project KU We thnk Mrs. Nsim Kroegel nd Dr. Ulrich Schefer for linguistic review of the mnuscript. 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Eur J Lipid Sci Tech 2011, 113: doi: / x Cite this rticle s: Strobel et l.: Survey of n-3 nd n-6 polyunsturted ftty cids in fish nd fish products. Lipids in Helth nd Disese :144. Submit your next mnuscript to BioMed Centrl nd tke full dvntge of: Convenient online submission Thorough peer review No spce constrints or color figure chrges Immedite publiction on cceptnce Inclusion in PubMed, CAS, Scopus nd Google Scholr Reserch which is freely vilble for redistribution Submit your mnuscript t