Results Analysis of the pasture is outlined in Table 1 and is limited to total number of species present and the three most dominant species found.

Transcription

1 Effect of psture type on lmb product qulity i F. M. Whittington 1, R. Dunn 2, G.R. Nute 1, R. I. Richrdson 1 nd J.D. Wood 1 1 Division of Frm Animl Science, Deprtment of Clinicl Veterinry Science, University of Bristol, Lngford, North Somerset, BS4 5DU, UK, 2 Institute of Grsslnd nd Environmentl Reserch, North Wyke Reserch Sttion, Okehmpton, Devon, EX2 2SB, UK Introduction There is much necdotl evidence of distinctive flvour in lmb met when the nimls re rised on trditionl extensive grzing systems, nd this influence of psture is often quoted in dvertising when met is sold through locl butchers, frmer s mrkets, nd by direct internet or frm-shop sles. In order to substntite these clims, there hve been number of scientific studies to identify dietry components tht re linked to differences in lmb flvour. In study t Bristol, Fisher et l. (2) showed tht there ws significnt difference in lmb flvour between nimls finished on either grss or concentrtes, with the concentrte-fed lmb met being higher in bnorml flvour, mmoni, bitter, metllic nd rncid ttributes, nd lower in norml lmb flvour nd overll liking. Young et l. (23) compred met from lmbs finished on rye-grss/clover psture, or either dried lucerne or mize concentrte, nd found tht the flvour profiles were quite distinct, with psture-fed lmb scoring higher in sheepmet flvour nd lower in brnyrd nd oily/ftty ttributes. This ltter study lso demonstrted differences in flvour voltiles, sktole nd 4- & 3-methylphenols in dipose tissue being higher in psture-fed rms compred to concentrte-fed rms, which in turn, hd higher levels of brnched chin ftty cids thn the psture-fed group. In ddition to these compounds, trils involving feeding protected lipid sources to ruminnts hve shown tht long chin polyunsturted ftty cids ( PUFA) re lso implicted in the development of flvour compounds during cooking of the met (Elmore et l. 2). When compring different psture types, most studies hve used grzing which ws often comprised of 1 or 2 species, for exmple, Shorlnd et l. (197) studied 2 vrieties of white clover; Prk et l. (1972) compred lucerne to phlris grss. The present study ims to determine whether grzing pstures high in biodiversity of botnicl species results in met tht is different in ftty cid composition nd eting qulity, to tht from lmbs rered on more conventionl ryegrss bsed psture. Mterils nd Methods Three unimproved grzing types were identified s sltmrsh, hether, nd moorlnd. These were evluted for plnt species nd dominnce of cover by the Institute of Grsslnd nd Environmentl Reserch. Semi-improved neutrl dry grsslnd comprised of t lest 8% ryegrss ws selected s control psture. Groups of 1 Scottish Blckfce wethers were rised nd finished on hether nd moorlnd pstures, nd 1 Suffolk Mule cross wethers on sltmrsh nd 9 on semi-improved psture. All lmbs were on their respective pstures for minimum of 1 dys before trnsport to the University of Bristol EU-pproved bttoir for slughter. Hot nd cold crcss weights were recorded nd ph mesurements tken t 45mins (initil) nd 24hrs (finl) post-slughter. Crcsses were chilled overnight t 1 C before butchery nd lloction of smples for nlysis. Loins were vcuum pcked nd conditioned for 1 dys t o C before removl of the bone, re-vcuum pcking nd freezing t -2 C witing sensory ssessment s described by Vtnsever et l. (2). Two 2cm leg steks were vcuum pcked nd conditioned for 1 dys t O C before re-pcking in modified-tmosphere (8% O 2 /2%CO 2 )for colour mesurements under simulted retil disply conditions of 1 lux, 16hrs on, 8hrs off, t 4 O C, (Vtnsever et l. 2). Mesurement of lipid oxidtion (TBARS vlue) ws mde t 7 dys of disply by the modified method of Trldgis et l. (196). Ftty cid composition of m. semimembrnosus muscle ws nlysed s described by Teye et l. (26) nd Vitmin E concentrtion using the method of Liu et l. (1996). Sktole ws mesured in voltiles obtined from simultneous distilltion-extrction of subcutneous ft using Likens-Nikerson condensers, s described by Whittington et l. (24). Sttisticl nlysis of dt ws crried out using one-wy nlysis of vrince (SPSS, Version 11.) Results Anlysis of the psture is outlined in Tble 1 nd is limited to totl number of species present nd the three most dominnt species found. Tble 1 Identifiction of botnicl species present in the psture Sltmrsh Hether Moorlnd Totl no. species Dominnt species Lolium perenne Cynosurus cristtus Holcus lntus Festuc rubr Armeri mritim Juncus mritimus Cllun vulgris Vccinium myrtillus D. flexuos Festuc ovin D. flexuos Nrdus strict There were no significnt differences in hot or cold crcss weight between lmbs from the different pstures lthough the sltmrsh lmbs were slightly hevier thn the other groups (Tble 2). Initil ph vlues were not different lthough finl ph vlues were higher in control nd moorlnd lmbs thn hether nd sltmrsh lmb (P<.1). There were no

2 differences between groups in conformtion score (ll men vlues close to clss R) but the hether nd moorlnd lmbs were ftter (men vlues close to clsses 3L nd 3H, respectively) thn control nd sltmrsh lmbs (men vlues close to clss 2) (P<.1). Tble 2 Crcss dt Crcss mesurements Sltmrsh Hether Moorlnd SED Sig. Hot Weight (kg) ns Cold Weight (kg) ns Initil ph (45 mins) ns Finl ph (24 hrs) b b.49 *** Conformtion Score ns Ftness Score b 12.8 b.788 *** Mens within rows with different superscripts differ significntly, ***= P>.1. ns =not significnt EUROP. Numericl conversions of clsses used for sttisticl nlysis: conformtion scle E = 5, U = 4, R = 3, O = 2, P = 1; ftness scle 1 = 4, 2 = 8, 3L = 11, 3H = 13, 4L = 15, 4H = 17, 5 = 2 Colour mesurements on the m. semimembrnosus muscle of leg steks showed tht met from the control group of lmbs remined cceptble (chrom >18) for 2 dys longer under retil disply conditions thn the other three groups which fell below the cceptble level t 8 dys (Figure 1). Figure 1 Colour shelf life mesurements Tble 3 Vitmin E nd lipid oxidtion products fter 7 dys retil disply Chrom Sltmrsh Hether Moorlnd Slt mrsh Hether Moorlnd Vitmin E b 4.78 ** TBARS ns P Dys displyed Anlysis of lipid oxidtion products (TBARS) reveled there ws no significnt difference between the four psture groups due to high vrition in the control lmbs, nd ll groups were below 2, the level t which lmb met is considered to be pproching incipient rncidity (Tble 3). However, if the ANOVA ws repeted using logrithmic trnsformtion of the dt, then the control nd hether lmbs hd significntly lower levels of TBARS thn the hether nd moorlnd groups (P<.1, dt not shown). Vitmin E levels were unusully high in met from the hether-fed lmbs compred with tht from the other 3 psture types which were lso high compred to those levels found in recent study by Turner et l., (22) where lmbs were fed lflf or ryegrss (2.5 nd 2.15mg/kg respectively) nd by Kspidou (23). Sensory nlysis of griddled loin steks by trined tste pnel showed tht met from the control lmbs scored higher in bnorml odour of the ft, bnorml flvour of the len, nd ws considered more rncid (Tble 4). Toughness score nd hedonic liking scores were not different between the psture groups, lthough the control-fed group ws rted slightly lower thn the others (dt not shown).

3 Tble 4 Sensory ttributes of cooked lmb (scored on scle of 1-1) Attribute Sltmrsh Hether Moorlnd Sig. Ft Abnorml odour 2. b ** Len Lmb flvour b b * Abnorml flvour 22.9 b 19.2 b * Rncid 14.7 b 11.2 b ** Sktole (ng/g ft) All lmbs ns Minus outlier* 83.4* *.59 There were no significnt differences in sktole concentrtions in ft tissue, due in prt to the presence of n outlier in ech of the control nd moorlnd groups (442.5 nd respectively). If these nimls were left out of the sttisticl nlysis, then the control nd sltmrsh lmb re found to contin lmost twice the level of sktole thn the hether nd moorlnd lmb, lthough there ws still sufficient vribility present to prevent this from being sttisticlly different (Tble 3). Regression nlysis of sktole concentrtion ginst bnorml odour score of the ft demonstrted tht sktole ccounted for 16.6% of the vrition in bnorml odour (r=.46, P<.1) Brnched chin ftty cid nlysis hs yet to be completed. Proportions of muscle lipid clsses nd composition of n-6 nd n-3 ftty cids (FA) re shown in Tbles 5 nd 6 respectively. Tble 5 Clsses of ftty cids in m. semimembrnosus Tble 6 Proportions of n-6 nd n-3 ftty cids in (mg/1g tissue) PUFA of m. semimembrnosus Sltmrsh Hether Moorlnd Sig. Totl FA ns SFA ns MUFA ns PUFA b 236 b ** Sltmrsh Hether Moorlnd Sig. C18:2 n b 3.14 ** C2:3 n b.14 b ** C2:4 n c 1.36 b *** C22:4 n b.6 b *** C18:3 n ns n-6 PUFA b 158 c 132 b *** n-3 PUFA ns C2:5 n ns C22:5 n ns C22:6 n b.32 b *** SFA, MUFA nd PUFA = sturted, mono-unsturted nd poly-unsturted ftty cids respectively. The mount of lipid or mrbling ft present in the m. semimembrnosus ws not different between the psture groups, lthough hether nd moorlnd lmbs tended to hve less lipid thn the control nd sltmrsh groups. This ws lso true for totl sturted nd monounsturted ftty cids. However, polyunsturted ftty cids (PUFA) were significntly higher in hether nd moorlnd lmbs due lmost entirely to higher n-6 ftty cids. Hether nd moorlnd lmbs were very similr in proportions of ll n-6 PUFA, except linoleic (C18:2, n-6) nd rchidonic (C2:4, n-6) cids which were significntly higher gin in hether-fed lmbs. n-3 PUFA were not different between the four psture groups except

4 docoshexenoic cid (DHA, C22:6, n-3) which ws lmost 2-fold higher in hether nd moorlnd lmbs thn control nd sltmrsh lmbs. Nutritionlly importnt ftty cid rtios n-6/n-3 nd P/S (PUFA/SFA) re shown in Figure 2. Figure 2 Ftty cid rtios in control (C), sltmrsh (S), hether (H) nd moorlnd lmb m. semimembrnosus muscle n-6/n-3 (idelly<4.) P/S (idelly >.4) 1.6 b***.25 b * b C S H M C S H M n-6/n-3 = Σn-6/Σn-3 P/S =Σn-6 + n-3 PUFA / Σ C12:+C14:+C16:+C18: SFA The n-6/n-3 rtio ws significntly higher in hether-finished lmb thn ll other groups, due lmost entirely to the high levels of linoleic cid present, nd ll nimls were below the recommended vlue of <4.. The rtios of PUFA to SFA (P/S) were ll lower thn the recommended vlue of >.4, lthough hether nd moorlnd lmb were significntly higher thn control nd sltmrsh lmb. The reltionship between vccenic cid (trns-c18:1) nd the nti-crcinogenic conjugted linoleic cid (CLA, 9-cis, 11-trns isomer) demonstrted in beef by Stonehouse et l. (24) is lso present in lmb muscle (Figure 3). These levels of CLA re similr to those found by E. Kspidou (23). Figure 3 Effect of psture type on the reltionship between trns-c18:1 nd CLA in m. semimembrnosus muscle of lmbs (mg/1g tissue) 8 CLA Moorlnd R 2 =.614 Sltmrsh R 2 =.8828 R 2 =.83 Hether R 2 = Trns C18:1 Although the trend-line for moorlnd lmb ppered higher thn the other three psture groups, the slopes nd intercepts were not significntly different due to insufficient numbers of nimls. However, nlysis of co-vrince

5 showed tht when trns-c18:1 ws used s the co-vrite, the levels of CLA were significntly higher in the moorlnd lmb group (Tble 7). Tble 7 Effect of psture on CLA levels in semi-membrnosus muscle of lmbs using trns-c18:1 s co-vrite Sltmrsh Hether Moorlnd Sig. CLA, mg/1g muscle b ** Conclusions All pstures exmined produced lmb of good eting qulity nd shelf life chrcteristics. Prticulrly noticeble were the high vlues for vitmin E compred with other published work, especilly where concentrte feeding ws employed. The vlue of 7mg/kg in the hether group is much higher thn previously reported. Eting qulity ssessment by trined tste pnel scored ll lmbs reltively high in flvour, prticulrly moorlnd nd sltmrsh lmb, with the semi-improved psture group hving the lowest score. In ddition, this ltter group hd the highest bnorml odour score of ft nd bnorml flvour of len, which ws only prtly ttributble to higher sktole levels in the dipose tissue. The fct tht these control lmbs hd the lowest concentrtions of PUFA my ffect the production of norml lmb flvour compounds, since ftty cid nlysis of the met reveled tht hether nd moorlnd lmb were significntly higher in ll n-6, nd in C22:6, n-3 PUFA. Moorlnd lmb ppered to be prticulrly rich in CLA (9-cis, 11-trns), n incresingly importnt ftty cid with implictions for humn helth. These results therefore provide further evidence tht grss fed lmbs hve high met qulity, nd some evidence tht diversity in botnicl composition in the psture confers specific differences tht could form the bsis of premium qulity mrketing schemes. Acknowledgements These studies were conducted s prt of the Rurl Economy nd Lnd Use reserch project Eting biodiversity: n investigtion into the links between qulity food production nd biodiversity protection, funded by BBSRC, NERC nd ESRC, with co-sponsorship from SEERAD nd DEFRA, involving the Universities of Exeter nd Bristol nd the Institute of Grsslnd nd Environmentl Reserch, North Wyke. References Elmore, J.S., Mottrm, D.S., Enser, M. nd Wood, J.D. 2. The effects of diet nd breed on the mjor voltiles present in lmb rom. Met Science, 55, Fisher, A.V., Enser, M., Richrdson, R.I., Wood, J.D., Nute, G.R., Kurt, E., Sinclir, L.A. nd Wilkinson, R.G. 2. Ftty cid composition nd eting qulity of lmb types derived from four diverse breed times production systems. Met Science, 55: Kspidou, E. 23. Vitmin E, selenium nd met qulity in sheep. PhD Disserttion, University of Bristol. Liu, Q., Scheller, K.K., nd Schefer,D.M Technicl note: A simplified procedure for vitmin E determintion in beef muscle. J. Anim. Sci. 74: Prk, R.J., Corbett, J.L. nd Furnivl, E.P Flvour differences in met from lmbs grzed on lucerne (Medicrgo stiv) or phlris (Phlris tuberos) pstures. Journl of Agriculturl Science, Cmbridge, 78: Shorlnd, F.B., Czochnsk, Z., Moy, M., Brton, R.A. nd Re, A.L Influence of psture species on the flvour, odour nd keeping qulity of lmb nd mutton. Journl of the Science of Food nd Agriculture: 21, 1-4. Stonehouse, G.G., Wood, J.D., Scolln, N.D., Wrren, H.E., Whittington, F.M. nd Richrdson, R.I. 24. Effects of grss silge nd concentrte diet on CLA levels in beef dipose tissue. Proceedings of British Society Animl Science, 15. Trldgis, B.G., Wtts, B.G., Younthn, M.T. nd Dugn Jr., L A distilltion method for the quntittive determintion of mlonldehyde in rncid foods. J. of Am. Chem. Soc., 37: Teye, G.A., Sherd, P.R., Whittington, F.M., Nute, G.R., Stewrt, A. nd Wood, J.D. 26. Influence of dietry oils nd protein level on pork qulity. 1. Effects on muscle ftty cid composition, crcss, met nd eting qulity. Met Science, 73: Turner, K.E., McClure, K.E., Weiss, W.P., Borton, R.J. nd Foster, J.G. 22. Alph-tocopherol concentrtions nd cse life of lmb muscle s influenced by concentrte or psture finishing J. Anim. Sci. 8: Whittington,, F.M., Nute, G.R., Hughes, S.I., McGivn, J.D., Len, I.J., Wood, J.D. nd Dorn, O. 24. Reltionships between sktole nd ndrostenone ccumultion nd cytochrome P452E1 expression in Meishn x Lrge White pigs. Met Sci. 67: Young, O.A., Lne, G.A., Priolo, A. nd Frser, K. 23. Pstorl nd species flvour in lmbs rised on psture, lucerne or mize. Journl of the Science of Food nd Agriculture, 83: i Whittington, F.M., R. Dunn, G.R. Nute, R.I. Richrdson nd J.D. Wood, (26) Effect of psture type on lmb product qulity. 9 th Annul Lngford Food Industry Conference, New Developments in sheepmet Qulity th My, Bristol, UK. Proceedings of the British Society of Animl Science, P