Fourie, S.J.

Klingbiel, J.F.G.

Naude, R.T.

English

AJOL - African Journals Online

S. Afr. J. Anim. Sci. 7, 5l *54 ( 1977)EFFECT OF TECHNIQUE OF ELECTRICAL STUNNING ON MUSCLE pH ANT)MEAT QUALITY CHARACTERISTICS OF BACON PIGSDuring the course of surveys on the occurrence ofPSE (pale, soft and exudative) pork at 6 pig slaughtercentres in the Republic of South Africa, it was ob-served that the manner in which pigs were electricallystunned, varied markedly within and between centres.It was observed that the electrodes of the stunning in-strument were not always applied directly to the templesof each pig and it so happened that pigs were electrical-ly shocked for as long as 45 s on various parts of thebody (Klingbiel, 1975). Lister (1970) and Ratcliff(1971) suggested that unskil led application of electricstunning of pigs could posible have undesirable effectson the eventual meat quality. Bendall (1966) demon-strated that direct electrical stimulation of excisedmuscle leads to an accelerated rate of post mortemglycolysis. ICingbiel & Naudd (19?6) showed that stressimmediately prior to slaughter also affects the rate ofpost mortem glycolysis in muscle which results in a palecolour and increased cooking loss of the meat.It was decided to investigate, under experirnentalconditions, the effect of unconventional electrical stun-ning. as being practised in industry, on post nutrtenrReceipt  o l  MS. 28.3.1977muscle glycolysis, rigor development, temperature,colour as well as cooking loss of the muscles of baconerpigs.hocedureEighteen l-andrace x large White baconer pigs,raised under standard conditions, were used for this ex-periment. On reaching a l ive mas of 82 t5 kg, feed waswithheld for one day from 2 previously selected pigsprior to slaughter. One pig was stunned in the normalway with an electric stunner (90 V) while the otherwas stunned abnormally. The treatments were randomlyallocated. Nine pairs were slaughtered in this manner.Control plgs (Normal stunning)The electrodes of the electric stunner were appliedto the moistened temples of the pig for 15 seconds.Treated prgs (Abnormal stunning)Before stunning the entire pig was sprayed withwater to ensure proper electrical contact. The electrodesJ.F.G.  Kl ingbie l ,  R.T.Naud6 and S.J.  Four ieAnimtl and DairJ., Science Research Institute, Irene, 1675OPSOMMTNG. INVLOID VAN TEGNII ,K VAN I ILE,KTRIESE BEDWELMING OP SPIER PH EN VLEISKWALITI ] ITSEIF.NSKAPPI:VAN SPEKVARKT.'n Elektr iese bedwelmer is  gebrurk om lB Landras x Grootwi t  spekvarke te bedwelm waartydens 9 varke met 'n normale tegniekbedwelm is (kontrole) en 9 ander op 'n abnormale manier deur die elektrodes vir 45 s op verskil lende dele van die vark se liggaarn teplaas (behandeld). Na slagting is die pl{, temperatuur, rigor, relleksie en gaarmaakverhese van spiere bepaal. Op geen een van die tyd-st ippe nl .  0,25;0,50;0,75;  l ;  3;  4 en 24 h post  mortetn,  het  d ie pt{  van die M. bngissimus lumborum stat is t iesbetekenisvol  tusen be-handelings verskil nie. Die pH, -waarde (45 minute post mortemJ van did spier was 6,30 t 0,068 vir die kontrole en 6,2? t 0,059 vir diebehandelde varke. Op dieselfde tydstippe post mortem, was die pI{ van die M. semimembranosus statisties betekcnisvol laer (P < 0,05)in die behandelde as in die kontrole varkc. Die pHr-waarde van die M. semimembranosus was 6.36 t 0,050 vir die kontrole en6.22 +0,030 v i r  d ie behandelde varke (P'  0,05).  Rigor van die M. semimembronosus was 7,9 +0,44 mm vir  d ie kontro le en 10,0 t  0,52 mm virdie behandelde varke (P < 0,01). Tussen behandelings was daar geen verskil le in spiertemperatuur, refleksie of gaarmaakverlies nie.Alhoewel abnormale toepassing van elektriese bcdwelming soosgebruik rn hierdie eksperitnentdie posr mortem pH van die M semimem-brsnosus verlaag het, het dit nie die ekonomiese belangrike eienskappe, refleksie en gaarmaakverlies nadelig beihvloed nie.SUMMARYNine Landrace x I arge White baconer pigs were stunned in the usual way by means of an electric stunner (control, normal stun-ning) while 9 other pfu1s were stunned in an unconventional way by applying an electric current for 45 s to various parts of the body(treated, abnormal stunning). Following slaughter" the pH, temperature,rigor, retlectance and cooking loss of muscles were determined.A t  no t  one  o f  thes tagesv iz .0 .25 ;0 ,50 ;0 ,75 ; l ; 3 :4  and ,24  h  pos t  mor tem the  pH o f  the  M.  l ongks imus  lumborum d i f f e red  s ta t i s t i ca l l ys igni f icant ly  between t reatments.  The RH, was 6,30 i -  0,068 for  the contro l  and,6,22 !  0,059 l 'or  the t reated prgs.  The post  mortempH of the M. semimernbranosus was statistically significantly lower in the treated than in the control pigs at the afore-mentioned stages.The pHt of  the M. semimembranosts was 6,36 +0,050 for  the contro l  and 6,22 t  0,030 for  the t reated pigs (P < 0,05).  Rigor of  theM . s e m i m e m b r a n o s u s  w a s 7 , 9  t 0 , 4 4 m m f o r t h e c o n t r o i a n d l 0 , 0 t 0 . 5 2 m m t o r t h e t r e a t e d p i g s ( P  < 0 , 0 1 ) . N o s i g n i f i c a n t d i f f e r e n c e swere found in muscle temperature, reflectance or cooking loss between treatments. This led to the conclusion that although post mor-tem pH was lowered rn the M" semimembranosus, the unconventional way of electrical stunning as applied in this experiment had nodisadvantageous effects on the economically important characteristics namely reflectance and cooking loss.,51of the stunner were applied to the temples of the pigfor l5 s followed immediately by placing the electrodeson the loin area (M. longissimus lumborum) for 10 s,followed by 5 s on the harn (M. semimembranosls andrt[. biceps femois). The stunned pig was dragged fromthe stunning pen to the bleeding area (4 metres). Theelectrodes were then placed on the ham for a further 5 s,causing the hindleg to extend, facilitating easier shacklingas noticed at some commercial abattoirs. Immediatelybefore hoisting, the electrodes were applied to thetemples again for l0 s. Simulating the stururing pro-cedure followed at certain slaughter centres (Klingbiel,197 5) the animal was exposed to the electric currentfor 45 s i.e. 25 s on the temples and 20 s on the loinand ham areas.After stunning, all the pigs were bled, scalded andeviscerated in a similar rnanner. Samples of the M.longissimus lumborum and M. semimembranosus wereexcised from the carcases within 8 minutes post mor-tem and these samples kept at 37oC in a moist atmo-sphere saturated with nitrogen for 6 h. The course ofpost mortem glycolysis was followed by measuring thep H  o f  t h e  m u s c l e  s a m p l e s  a t  0 , 2 5 ; 0 , 5 0 ; 0 , 7 5 ; l ; 2 ; 3 ;4; 5 and 6 h post mortem. The remainder of the sampleswere then stored in a refrigerator at2oC for 18 h follow-ing which the final pH was measured at 24 h postmortem. The technique used to determine the pErigor, temperature, reflectance and cooking loss of thernuscles, were those as described by Klingbiel & Naudd(1976). An analysis of variance (Snedecor, 1966) wasperformed on the data.MuscleResults and discussionMuscle pHThe pH-values of the M. longissimus lumborumand M. semimembranosus, measured at different stagespzst mortem, are given in Table I .The data in Table I indicate that difference inthe pt{-values of the M. longissimus lumborurn betweenthe treatments was statistically significant only at2hpost mortem (P < 0,05).The pH1-values (0,75 h post mortem) were 6,30and 6,22 (difference not statistically significant for thecontrol and treated groups respectively.The pH-values of the M. semimembronosus of thetreated group were statistically significantly lower thanin the control  group at  0,25; 0,50; 0,75; l ;3 and 4 hpost mortem. The pH1-values were 6,36 and 6,22 for thecontrol and treated groups respectively (P < 0,05).At 2 h post mortem the difference was statisticallyhighly significant (P < 0,01).At 5; 5 and 24 h post mortem there were nosignificant differences in pH-values for both musclesbetween treatments. This indicates that muscle pH-values of the 2 groups had already reached similar levelsafter 4 h post mortem which agrees with previous find-dings (Klingbiel & Naudd, 1976).It is generally accepted that the M. longissimuslumborum artd M. semimembro,nosus. with a low muscleTable IEffect of technique of electrical stunning on post mortem muscle pHaM. lonxissimus lumborum M. semimembranosusAbnormalstunning (n =9)Time posrmortemControls(n  =9 )0 ,25  h0 ,50  h0 ,75  hl h2 h3 h4 h5 h6 h2 4 h6,41 + 0 ,0466,34 + 0 ,0606,30 + 0 ,0686,30 + 0 ,0576 , 1 7  +  0 , 0 5 25 ,87  +  0 ,0955 ,60  +  0 ,0935 ,40  +  0 ,0675 , 2 9  +  0 , 0 3 15 ,28  +  0 ,0336,36 + 0 ,0466 ,27  +  0 ,0526 ,22  +  0 ,0596 ,17  +  0 ,0695 , 8 8  +  0 , 1 1 95 . 6 s  t  0 , 1 3 45 ,48  +  0 ,1265 ,43  +  0 ,0985 ,34  +  0 ,0845 ,28  +  0 ,0376 ,15  t  0 ,4695 ,93  t  0 ,0615 ,61  +  0 ,0735,40 + 0 ,0795,34 + 0 ,0465 ,29  +  0 ,0345 ,27  t  0 ,0385,99*l )  1 1 * *6,09*4 ,95  *1 , 4 71 ,5 "10 ,21) ) 15,09*1 , 7 60 ,s90,0490 ,0510 , 1 l 20 , 1  2 l0 , 1 0 80,0340,034a Mean of three pH-nreasurements  standard error* ' r  P . .  0 ,01 = 8 ,28*  P ' 0 , 0 5  =  4 " 4 1Controls( n  = 9 ) Abnormal stunnins52pH and high muscle temperature at 45 minutes poslmortem (Briskey, 1964; Mcloughlin, 1965) are 2 ofthe muscles particularly inclined to develop poor meatquality characterist ics.From the results in this paper it is clear however,that the post mortem pl7-values of the M. semimem-branosus were affected more severely tiran those ofthe 44. longissimus lumborunr, which is in agreementwith some of the findings of Eikelenboom (197a). Hefound that under certain conditions the pcsst mcrtempH of the tvl. semimembranosus can be lower than or thesame as the pll of the M. longissimus lumborum Lawrie(1960) mentions that struggling of the anirnal duringslaughter causes the post mortem pll of certain othermuscles to be lower than that of the M. longissimuslumborum. The additional electric current applied tothe ham of the treated pigs in this experirnent mostprobably caused the M. sentimembranosus to respond toa greater extent than the h{. longissimus lumborum interms of rate of post mortem glycolysis.Table 2 contains the results of the other meatq uality characteristics.Table 2Efl'ect of technique of electrical stunnirtg oncertain muscle cltarac't eristics aCharacter is t icCt ln l ro ls Abnormal(n  =9 )  s tunn ing  { r r  =9 )I ; -valueRigorAccording to the data in Table 2 the rigor-valueof l0 mm measured on the M. semirnembranosus of thetreated pigs was statistically significantly higher than tire'7,9 mm measured for the control pigs (P . 0,01).Sybesma (1966) and Klingbiel & Naudd (1976) similar-ly found higher rigor-values in muscles with low ptil-values.ReflectanceThere were no significant differences in reflect-ance values between treatments (Table 2). Irlcl-oughlin& Coldspink (  1963) ment ioned that sarcoplasmic pro-tein precipitation, which masks the colour of the musclcmyoglobin and therefore gives meat a paler appearance.is due to a combined effect of low pH and high muscletemperature. Lister ( 1970) also states that the change inmuscle colour appears to be a function of muscle tern-perature when a particular pH-value is reached. Ir{cDou-gall & Disney (1967) recorded high reflectance valuesin muscles with a low pH, concomitant with a hightemperature.Although a significantly (P .. 0,05) lower ;rosrnnrtem pH of the lvI. semimcmbronofits was found inthis experiment (Table I ), the muscle temperaturewas not significantly affected and this could probablybe the reason why the reflectance oi the muscles was notaf-fected ifferently by the 2 treatments. It is also pos-sible that the pH-values, which remained near 6 evenafter 2 hours storage, prevented any large precipitationof sarcoplasmic proteins.Cooking lossThe cooking loss of 100 g meat samples did notdiffer between treatments. Higher drip loss, poorerwater binding capacity and therefore a higher cookingloss, are caused by a combination of high temperatureand low pH in the muscle (Wismer-Pedersen, 1969;Uster, 1970). These conditions ciid not prevail in themuscles of the treated animals, hence the result that nodifferences were observed in the cookinq loss of themuscles of the two groups of pigs.ConclusionsLlnconventional electric stunning as applied inthis experiment, caused the rate of post mortem pHdecline in the llI. semirnembranctsrzs to be signific:rntlyincreased. "fhe experimental treatment was however notof such a drastic nature as to lower the pt{ of the M.Irtngissimus lumborum or cause a higher muscle tem-perature in ei ther of  the 2 muscles.  Consequent ly ' ,  re-f lectance and cooking loss of  the meat were not de-trinrentally affected by the abnormal electrical stunningof pigs. The more rapid pl{-fall in t}re ,M. s(ntirncmhro-T+s  LL  (oc )T45 SM (oC)Rigor SM (mm)Ref lectance L.L (%)Ref lectance SM (%\Cooking loss LL (  %)Cooking loss SM ( %)38,5 - f  0 ,393 8 , 6  +  0 , 3 37,9 r  0 ,443 t , 4  t  0 , 9 532,1 t -  1 ,3928 ,5  t  0 ,692 8 , 9  t  | . 2 138 ,2  t  0 ,4338 ,5  J  0 ,421 0 , 0  t  0 , 5 232 ,4  t  0 ,63299 t  1  ,9429 ,8  t  0 ,762 8 , 8  t  l , 0 80 ,370,04l 0 , l  4 i  '0 , 591 , 4 3t , 7 40 ,01a Mean value t  s tandard errotT45 Muscle temperature 4,5 minutes post  mortemLL bf . longissimus lumborumSM M" semimembranotusi * P . , : 0 , 0  I  =  8 , 2 8P . -  0 ,05  =  4 ,41Muscle temperotureThere were no stat ist ical ly signif icant dif ferencesin muscle temperature between treatments. Van Log-test i jn  (1969)  mainta ins that  a  low meat  qual i ty ,  o fwhich an accelerated rate of post mortem muscle pHfall is a symptom, is not necessarily accornparried by arise in muscle temperature. Therefore, although the ab-normal way of electr ical stunning in this experimentdecreased the pH of the . lL senimembranosus, i t  wasnot  suf f ic ient  to  increase the musc le  temperature.s3nosus of the treated pigs. does however point to the stsceptible pigs. Had stress susceptible pigs been used,stress effect on muscles which are electrically stimulat- one would expect that they would have been moreed. readily affected by this particular way of electricalSince stress resistant pigs were used in this experi- stunning than stress resistant pigs, possibly by show-ment, one could only speculate on the effects which ing a faster rate of pH-decline, higher reflectance andthe experimental treatment would have had on stres greater cooking loss.ReferencesBENDALL, J.R., 1966. The effect of pre-treatment of pigs with curare on the post-mortem rate of pH fall and onsetof rigor mortis in the musculature. /. Scl. Fd Agric. 17 , 333-338.BRISKEY,EJ., 1964. Etiological status and associated studies of pale, soft, exudative porcine musculature. Adv. FdR e s .  1 3 , 8 9 - 1 7 8 .EIKELENBOOM, G., 1974. Vleeskwaliteit en stressgevoeligheid bij varkens. Vleesdistributie en Weestechnologie9( l  1 ) ,  36- -39 .KLINGBIEL, J.F.G., 1975. Faktore wat'n rol speel by die voorkoms van bleek, sagte en waterige varkvleis. M.Sc.( Agric.)-verhandeling. Univ. Pretoria.KLINGBIEL, J.F.G. & NAUDE, R.T., 1976. Effect of immediate preslaughter stress on certain meat quality charac-teristics of bacon pigs. Agroaninwlia 8,7 -12.LAWRIE, R.A., 1960. Post mortem glycolysis in normal and exudative longissimus dorsi muscles of the pig in rela-tion to socalled white muscle disease. J. comp. Path. 70,273-295.LISTER, D., 1970. The physiology of animals and the use of their muscle for food. ln: The physiology and biochemistryof muscle as a food, Yol.2, ed. E.J. Briskey, R.G. Casens & B.B. Manh. Madison: Univ. Wisconsin Press.MacDOUGALL, D.B. & DISNEY, J.G., 1967. Quality characteristics of pork with special reference to Pietrain, Pietrainx landrace and landrace pigs at different weights. J. Fd Technol. 2,285-297.McLOUGHLIN, J.V., 1965. Studies on pig muscle.4. pH1 values in the longissimus dorsi muscle of pigskil ledundercommercial conditions. lr. J. agric. Res. 4, 151 -160.McLOUGHLIN, J.V. & GOLDSPINK, G., 1963. Post mortem changes in the colour of pig longissimus dorsi muscle.Nature (Lond. ) 198, 584-585.RATCLIFF, P.W., 1971. Review of papers. Section 2. Stunning. In: hoc. 2nd int. Symp. Condition Meat Qwlityftgs, ed. Jeannette C.M. Hesel-de Heer, G.R. Schmidt, W. Sybesma & P.G. van der Wal. Wageningen: Pudoc.SNEDECOR, G.W., 1966. Statistical methods. 5th ed. Ames: Iowa State Univ. Press.SYBESMA, W., 1966. Die Messung des Unterschiedes im Auftreten des rigor mortis in Schinken. F-Telschwirtschoft6 , 6 3 7  - 6 3 9 .VAN LOGTESTIJN, J.G., 1969. A high meat temperature - a cause or a symptomof meatdegeneration? ln: Recentpoints of view on the condition and meat quality of pigs for slaughter, ed. W. Sybesma, P.G. van der Wal &P. Walstra. Utrecht: Retroprint.WISMER-PEDERSEN, J., 1969. The pH-dependent water-binding capacity of pork muscle in relation to processing.In: Recent points of view on the condition and meot quality of pigs for slaughter, ed. W. Sybesma, P.G. vander Wal & P. Walstra. Utrecht: Retroprint.5 4

Effect of technique of electrical stunning on muscle pH and meat quality characteristics of bacon pigs

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Effect of technique of electrical stunning on muscle pH and meat quality characteristics of bacon pigs

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