Meat quality of electrically stimulated game under variable harvesting conditions in South Africa

Marais, Schutz (2013-03)

Thesis (MSc)--Stellenbosch University, 2013.


ENGLISH ABSTRACT: In South Africa, game species are harvested throughout the year under variable circumstances, presenting a wide range of temperatures and environmental conditions. The latter can include extremely cold (night harvesting – winter < 5°C) or extremely hot temperature conditions (day harvesting – spring > 35°C). These unique harvesting conditions can negatively affect the game meat quality. Electrical stimulation (ES) has become an important intervention in commercial abattoirs to maintain or improve the meat quality. Electrical stimulation was originally applied to prevent cold shortening (CS) of muscles (i.e. cold induced toughening of muscles) in extremely cold conditions (< 10°C), but ES is also applied to accelerate ageing and to decrease the variation in the quality of meat products. When ES of carcasses is combined with the use of post rigor rapid chilling techniques, it can be extremely beneficial to both the supplier and consumer of game meat. Unfortunately, limited research is available on the use of ES on African game carcasses. The objective of this study was therefore to investigate the effect of ES on the meat quality of South African game carcasses. The latter consisted of two trials: the aim of the first trial was to investigate the effect of ES on the meat quality of commercially harvested springbok M. longissimus dorsi (LD) during night harvesting conditions; and the aim of the second trial was to investigate the effect of ES and rigor temperature treatment (5°C and 39°C) on the meat quality of blesbok LD muscles over time. For the first trial, 35 springbok were harvested during commercial night harvesting operations. Electrical stimulation was applied on 16 springbok within 45 minutes post mortem, while 19 were non ES animals and therefor used as the control. The pH decline was recorded in the LD muscles until rigor, after which general meat quality analyses (pH, tenderness, cooking loss, purge loss and colour) were performed on days 2, 5 and 21 post mortem. The ES muscle samples had lower (P ≤ 0.05) initial pH values compared to the non ES samples, however, the pH decline profiles and ultimate pH values (pHu) were similar for both ES and non ES samples. For each time point and both genders, no differences (P > 0.05) were present in the mean muscle tenderness of the ES and non ES muscle samples. The purge and cooking losses did not differ (P > 0.05) between treatments for days 2 and 5, although on day 21 the storage purge losses were 5.20% ± 0.31 (ES) compared to 4.30% ± 0.31 (non ES). The retail colour stability and regression of the colour measurements over time also did not differ (P > 0.05) between treatments. However, the ES samples had a higher rate of increase in colour sharpness (chroma regression data) (0.567 ± 0.108) compared to the non ES samples (0.224 ± 0.099). It was postulated that ES did not enhance the desired meat quality attributes i.e. tenderness, due to various external factors (animal age, stress and time post mortem prior to stimulation) which could have resulted in varying results. In the second trial, 20 mature male blesbok were harvested of which 10 animals were ES within 45 minutes post mortem and 10 non ES animals were used as control specimens. Meat quality analyses (pH, colour, purge loss, cooking loss and tenderness) were also performed during this trial on days 0 (rigor), 1, 2 and 5 post mortem. Electrical stimulation decreased the initial pH decline as well as the time to the onset of rigor mortis. The mean pH of the 5°C ES (5.75 ± 0.07) and non ES muscle samples (5.98 ± 0.06) at rigor, were lower (P ≤ 0.05) compared to the ES (5.55 ± 0.14) and non ES samples (5.37 ± 0.03) at 39°C. At 5°C, the ES muscle samples (80.34 ± 5.64) were more tender (P ≤ 0.05) compared to the non ES samples (101.95 ± 4.59) at rigor, although no differences (P > 0.05) were present for days 1, 2 and 5. All of the 39°C ES muscle samples (rigor, 57.05 ± 5.20; day 1, 48.37 ± 3.68; day 2, 46.06 ± 3.56 and day 5, 39.94 ± 3.46) were more tender (P ≤ 0.05) than the non ES samples (rigor, 79.37 ± 9.48; day 1, 74.41 ± 5.40; day 2, 75.52 ± 7.11 and day 5, 66.18 ± 6.14). Electrical stimulation was therefore only successful at increasing the tenderness of the 5°C muscle samples at rigor, but ES was very effective at increasing the tenderness of the samples for each time point at the higher temperature treatment (39°C). The water holding capacity (WHC), cooking loss percentages and bloomed meat surface colour of the blesbok LD muscles were unaffected (P > 0.05) by ES. At each time point the 39°C muscle samples had lower (P ≤ 0.05) mean WHC compared to the 5°C samples. The mean purge losses were higher (P ≤ 0.05) in the non ES (7.13% ± 0.30) compared to the ES (4.89% ± 0.32) muscle samples. However, the mean purge losses were higher in the 39°C (7.31% ± 0.30) compared to the 5°C (4.67% ± 0.29) muscle samples. Additionally, the mean purge losses increased (P ≤ 0.05) over time (day 1, 4.63% ± 0.41; day 2, 5.91% ± 0.34 and day 5, 7.47% ± 0.39), which will possibly have negative affects on consumer perception of blesbok meat quality. The mean cooking loss percentages were higher (P ≤ 0.05) in the 39°C (26.93% ± 1.04) compared to the 5°C (21.33% ± 1.29) muscle samples at rigor, although the opposite was true for days 2 and 5 (5°C: day 2, 28.06% ± 0.67 and day 5, 27.72% ± 0.57; 39°C: day 2, 25.60% ± 0.56 and day 5, 25.65% ± 0.72). All of the 39°C bloomed colour measurement values were higher (P ≤ 0.05) compared to the 5°C samples and the former stayed more or less constant over time. Although the 5°C colour measurement values improved over time, it never reached similar values to that of the 39°C samples. The use of ES under commercial game harvesting conditions requires further investigation; since the expected positive effects on the meat quality parameters were not found to be conclusive in this study. Extremely high temperatures during the harvesting of South African game species will negatively affect most of the meat quality attributes of blesbok LD muscles, while extremely low temperatures will most probably only have a negative affect on muscle tenderness. The application of ES may hold great benefits for the South African game industry, but further research is essential to endorse the application of ES on game species and to manage the factors affecting its effectiveness during different harvesting conditions.

AFRIKAANSE OPSOMMING: Suid Afrikaanse wildsspesies word regdeur die jaar onder veranderlike omstandighede geoes. Daar is dus ‘n wye reeks temperatuur- en omgewingstoestande wat tydens die oes van wild ‘n rol speel, soos geweldige koue (< 5°C in winter tydens nag oeste) en geweldige warm (> 35°C in lente tydens dag oeste) omgewingstemperature. Die vleiskwaliteit van wildsspesies kan gevolglik negatief beïnvloed word deur dié omgewings toestande. In kommersiële abattoirs het elektriese stimulasie (ES) ‘n baie belangrike intervensie geword om vleiskwaliteit te behou of te verbeter. Elektriese stimulasie was oorspronklik vir die voorkoming van kouekrimping (koue geïnduseerde vertaaiing van spiere) van spiere tydens baie koue temperatuurkondisies (< 10°C) toegepas. Verder was ES ook toegepas vir die bespoediging van die verouderingsproses in karkasse asook om die variasie in kwaliteit tussen vleisprodukte te verminder. Die toepassing van ES, in kombinasie met versnelde post rigor verkoelingstegnieke, kan dus geweldige voordele vir beide die verskaffer en verbruiker van wildsvleisprodukte inhou. Daar is ongelukkig beperkte navorsing op die toepassing van ES op Afrika se wildskarkasse. Die doel van die studie was dus om die effek van ES op die vleiskwaliteit van Suid Afrikaanse wildskarkasse te bepaal. Laasgenoemde was vasgestel met behulp van twee proewe: die eerste proef se doelwit was om die effek van ES op die vleiskwaliteit van kommersieël geoesde springbok M. longissimus dorsi (LD) gedurende nag oes kondisies te bepaal; en die tweede proef se doelwit was om die effek van ES en rigor temperatuurbehandeling (5°C en 39°C) op die vleiskwaliteit van blesbok LD spiere oor tyd te bepaal. Vyf en dertig springbokke was tydens kommersiële nag oes toestande vir die eerste proef geoes. Elektriese stimulasie was binne 45 minute post mortem op 16 van die springbokke toegepas, die ander 19 diere was nie gestimuleer nie (nie ES) en het dus as die kontroles gedien. Die pH daling was in die LD spiere bepaal tot en met rigor, waarna die algemene vleiskwaliteit analises (pH, taaiheid, kookverlies, dripverlies en kleur) op dae 2, 5 en 21 post mortem bepaal is. Die ES spiere se aanvanklike pH-waardes was laer (P ≤ 0.05) as die van die nie ES spiere, maar die pH dalingsprofiele en die finale pH-waardes (pHu) was min of meer dieselfde (P > 0.05) vir die ES en nie ES spiere. Vir elkeen van die tydpunte en beide geslagte was daar geen verskille (P > 0.05) tussen die gemiddelde spiertaaiheid van die ES en nie ES spiere nie. Daar was ook geen verskille (P > 0.05) in drup- en kookverliese tussen behandelings vir dae 2 en 5 nie. Op dag 21 was die ES spiere se gemiddelde verpakkingsdripverlies persentasies (5.20% ± 0.31) wel hoër (P ≤ 0.05) as die nie ES spiere (4.30% ± 0.31). Daar was ook geen verskille (P > 0.05) in die kleurstabiliteit en die regressie van die kleurmetings oor tyd, tussen behandelings nie. Die ES spiere het wel ‘n hoër tempo van toename in die skerphied van die kleur (chroma regressie data) (0.567 ± 0.108) in vergelyking met die nie ES spiere (0.224 ± 0.099) getoon. Elektriese stimulasie het dus nie die verlangde vleiskwaliteit eienskappe (bv. taaiheid) verbeter nie, wat moontlik was as gevolg van verskeie eksterne faktore (die ouderdom van die diere, stress en die tyd post mortem voor stimulasie toegepas is) wat variasies in die resultate kon veroorsaak het. Daar kort dus meer navorsing met betrekking tot die toepassing van ES onder kommersiële wildsoeskondisies, omdat die verwagte positiewe effekte van ES op die vleiskwaliteit van wild in die studie nie onomwonde vasgestel is nie. In die tweede proef is 20 volwasse manlike blesbokke geoes. Daar is op 10 van die blesbokke ES toegepas binne 45 minute post mortem en die ander 10 is nie ES en het dus gedien as kontroles. Vleiskwaliteit analises (pH, kleur, dripverlies, kookverlies en taaiheid) is uitgevoer op dae 0 (rigor), 1, 2 en 5 post mortem. Elektriese stimulasie het ‘n afname in die aanvanklike pH daling sowel as ‘n afname in die tyd na die aanvangs van rigor mortis veroorsaak. The gemiddelde pH-waardes van die ES (5.75 ± 0.07) en nie ES (5.98 ± 0.06) spiere by die 5°C temperatuur behandeling by rigor was laer (P ≤ 0.05) as die ES (5.55 ± 0.14) en nie ES (5.37 ± 0.03) spiere by 39°C. By 5°C was die ES spiere (80.34 ± 5.64) sagter (P ≤ 0.05) as die nie ES spiere (101.95 ± 4.59) by rigor, maar daar was geen verskille (P > 0.05) in taaiheid tussen behandlings vir dae 1, 2 en 5 nie. Elkeen van die 39°C ES spiere (rigor, 57.05 ± 5.20; dag 1, 48.37 ± 3.68; dag 2, 46.06 ± 3.56 en dag 5, 39.94 ± 3.46) was sagter as die nie ES spiere (rigor, 79.37 ± 9.48; dag 1, 74.41 ± 5.40; dag 2, 75.52 ± 7.11 en dag 5, 66.18 ± 6.14). Elektriese stimulasie was dus suksesvol om die sagtheid van die 5°C spiere slegs by rigor te verbeter, maar die toepassing van ES het die sagtheid van die 39°C spiere by elke tydpunt verbeter. Elektriese stimulasie het geen effek (P > 0.05) op die waterhouvermoë (WHC), kookverlies persentasies en die vleisoppervlak kleur van die blesbok LD spiere gehad nie. Die WHC van die 39°C spiere was by elke tydpunt laer (P ≤ 0.05) as die van die 5°C spiere. Die nie ES spiere (7.13% ± 0.30) het gemiddeld hoër (P ≤ 0.05) dripverlies persentasies as die ES spiere (4.89% ± 0.32) gehad. Die 39°C spiere (7.31% ± 0.30) het wel beduidend hoër gemiddelde dripverlies persentasies in vergelyking met die 5°C spiere (4.67% ± 0.29) gehad. Die persepsie van die verbruikers van blesbokvleis kan moontlik negatief beïnvloed word deur die toename (P ≤ 0.05) in die gemiddelde dripverlies persentasies van die blesbok LD spiere oor tyd (dag 1, 4.63% ± 0.41; dag 2, 5.91% ± 0.34 en dag 5, 7.47% ± 0.39). By rigor was die gemiddelde kookverlies persentasies hoër (P ≤ 0.05) in die 39°C spiere (26.93% ± 1.04) in vergelyking met die 5°C spiere (21.33% ± 1.29), maar die teenoorgestelde was gevind by dae 2 en 5 (5°C: dag 2, 28.06% ± 0.67 en dag 5, 27.72% ± 0.57; 39°C: dag 2, 25.60% ± 0.56 en dag 5, 25.65% ± 0.72). Die vleisoppervlak kleurmetings van die 39°C spiere by elke dag (met tyd) was hoër (P ≤ 0.05) in vergelyking met die 5°C spiere en eersgenoemde het ook min of meer konstant gebly met tyd. Die vleisoppervlak kleurmetings van die 5°C spiere het wel verbeter met tyd, maar dit was nooit gelyk aan die waardes van 39°C spiere nie. Die gebruik van ES tydens die kommersiële oes van wild benodig verdere navorsing siende dat die verwagte positiewe effek op die vleiskwaliteit nie gerealiseer het nie. Die meerderheid van die vleiskwaliteit eienskappe van blesbok LD spiere sal negatief beïnvloed word deur die geweldige hoë temperature wat kan voorkom tydens die oes van Suid Afrikaanse wildsspesies. Wanneer geweldige lae temperature oorheers, sal net die taaiheid van die spiere moontlik negatief beïnvloed. Die toepassing van ES kan groot voordele inhou vir die Suid Afrikaanse wildsindustrie, maar verdere navorsing is nodig om die gebruik van ES op wildsspesies te motiveer en om die faktore wat die effektiwiteit van ES tydens die veranderlike oes omstandighede kan beïnvloed te beheer.

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