Ante- and post-mortem factors influencing impala (Aepyceros melampus) meat quality

Engels, Retha Annette (2019-04)

Thesis (MScAgric)--Stellenbosch University, 2019.


ENGLISH ABSTRACT: The aim of this research was to investigate the influence of sex, muscle (Longissimus thoracis et lumborum/LTL, biceps femoris/BF, semimembranosus/SM, semitendinosus/ST, infraspinatus/IS, and supraspinatus/SS), production system (intensive, semi-extensive and extensive), and post-mortem ageing on the meat quality of impala (Aepyceros melampus) to provide baseline data for the South African game industry. This was done by gathering data on the carcass yields, overall meat quality (physical attributes and chemical composition) and sensory meat quality of impala, as well as investigating the optimum post-mortem ageing period for maximum tenderness of LTL steaks. The sex-muscle comparison (Trial 1) consisted of 11 male and 11 female impala that were culled from a semi-extensive production system in the Central Sandy Bushveld region near Modimolle in Limpopo, South Africa. No sexual dimorphism (P > 0.05) was recorded for the undressed (36.4 ± 1.30 kg males; 37.8 ± 1.30 kg females) or dressed carcass weights (21.6 ± 0.82 kg males; 21.0 ± 0.82 kg females). However, male impala had a higher (P = 0.004) mean dressing percentage than females (59.1 ± 0.76 % vs. 55.6 ± 0.76 %). For the production system comparison (Trial 2), 12 sub-adult (±15- 18 months old) male impala were culled per production system (n = 36). The intensive and semiextensive production systems were also located near Modimolle, and the extensive production system was located in the Central Rûens Shale Renosterveld region near Bredasdorp in the Western Cape of South Africa. Extensive system impala had higher (P ≤ 0.05) undressed and dressed carcass weights (46.5 ± 1.12 kg and 26.6 ± 0.79 kg) than intensive (37.9 ± 0.92 kg and 21.9 ± 0.65 kg) and semiextensive system impala (36.4 ± 0.96 kg and 21.3 ± 0.68 kg, respectively), while the latter two systems did not differ significantly from each other. No differences (P = 0.364) were recorded between production systems for the dressing percentages (57.9 ± 0.58 % pooled mean) or total offal yields (39.7 ± 0.48 % pooled mean) of sub-adult male impala. The physical meat quality attributes of impala were significantly influenced by sex, muscle, and production system. Sex-muscle interactions were found for the CIE a* values, drip loss percentages and cooking loss percentages (Trial 1). Higher (P = 0.021) ultimate pH (pHu) values and lower (P = 0.002) Warner-Bratzler shear force (WBSF) values were recorded in male impala than in females. The IS and SS muscles from the forequarter were the most tender, whereas the BF and SM muscles from the hindquarter were the least tender. The pHu of both sexes, all muscles (Trial 1) and both intensive and semi-extensive system impala (Trial 2) fell within the acceptable normal range (5.6- 5.9), but the extensive system impala produced meat with an exceptionally high pHu (6.2 ± 0.06) due to extrinsic factors caused by the production and culling process. Consequently, extensive system impala produced meat with DFD-like (dark, firm, dry) characteristics, such as the lowest drip loss percentage (0.9 ± 0.14 %), cooking loss percentage (28.1 ± 0.79 %) and darkest, least red and least saturated surface colour (L* = 26.8; a* = 10.0; b* = 5.2; chroma = 11.4). With the exception of the extensive system impala, impala from both sexes, all muscles and both the intensive and semiextensive systems (Trial 1 & 2) had CIE Lab colour measurements within the acceptable range of expectation for game meat (L* = 30.9-36.8; a* = 11.4-13.6; b* = 6.0-8.8). Furthermore, all fresh impala meat in this study (Trial 1 & 2) produced meat with shear force values < 43 N (range of 19.2-39.3 N) at 24 hours post-mortem and may thus be classified as tender. The chemical meat quality of impala was also significantly influenced by sex, muscle and production system. Sex-muscle interactions were recorded for all four chemical components (moisture, protein, intramuscular fat/IMF and ash), while a strong negative correlation (r = -0.49; P < 0.001) was observed between the protein and IMF content of the muscles (Trial 1). Extensively produced impala were recorded to have LTL muscles with the lowest (P ≤ 0.05) mean IMF (1.5 ± 0.06 g/100 g) and the highest protein (23.4 ± 0.12 g/100 g) content, whereas intensive system impala had the highest IMF content (2.0 ± 0.05 g/100 g). The proximate composition of all impala meat in this study (Trial 1 & 2) ranged from 74.7-77.0 % moisture, 20.7-23.5 % crude protein, 1.2-2.2 % IMF and 1.1-1.3 % ash content. While the differences between sex, muscle and production system were significant, the differences were marginal and thus may not be of biological consequence with regards to human nutrition. Regardless, all impala meat had a high protein and low IMF content which is considered desirable by health-conscious consumers. With the differences in dietary regime, management strategies and daily activity between production systems, it can be expected that the sensory profile and fatty acid composition of impala meat will also be influenced by differences in these factors. The influence of production system on sensory meat quality was significant (Trial 2), with the highest (P ≤ 0.05) sensory ratings for gamey, beef-like, herbaceous and sweet-associated aromas and flavours found in extensive system impala during descriptive sensory analysis (DSA). However, the sensory meat quality of the intensive and semi-extensive system impala from the same production region did not differ (P > 0.05) except for a few textural attributes and a higher (P < 0.05) gamey flavour intensity found in semi-extensive system impala. The ideal post-mortem ageing period of impala LTL steaks was also determined. The LTL muscles of 11 male and 11 female impala (Trial 1) were divided into eight portions each, with each portion was randomly allocated to age for 1, 2, 4, 6, 8, 10, 12, or 14 days, vacuum-sealed and stored at 4°C. This research found that maximum tenderness (13.5 ± 0.91 N) and improvement of bloomed surface colour of impala LTL steaks was reached at eight days post-mortem, whereas prolonged ageing beyond this point resulted in some discolouration and no further improvement in meat tenderness. The ageing of meat to eight days post-mortem also successfully negated the initial significant differences in tenderness between the sexes. Therefore, it is recommended that impala LTL steaks should be vacuum-aged at 4°C for eight days to achieve optimum tenderness and minimize variability between individual animals irrespective of sex.

AFRIKAANSE OPSOMMING: Die doelwit van hierdie navorsing was om die invloed van geslag, ses spiere (Longissimus thoracis et lumborum/LTL, biceps femoris/BF, semimembranosus/SM, semitendinosus/ST, infraspinatus/IS, en supraspinatus/SS), produksiestelsel (intensief, semi-extensief en ekstensief) en nadoodse veroudering op die vleiskwaliteit van rooibokke (Aepyceros melampus) te ondersoek om sodoende basiese data rakende die vleisproduksie potensiaal van rooibokke aan die Suid-Afrikaanse wildbedryf te verskaf. Hierdie doel was uitgerig deur data te versamel oor die karkas opbrengste en algehele vleiskwaliteit (fisiese eienskappe en chemiese samestelling) van rooibokke soos beïnvloed deur geslag, spier en produksiestelsel, sowel as om die sensoriese profiele en vetsuur-samestellings van sub-volwasse rooibok ramme vanaf drie verskillende produksiestelsels te ondersoek, en die ideale verouderingsperiode van vakuum-verpakte LTL snitte vir maksimum sagtheid te bepaal. Die geslag- en spiervergelyking (Eksperiment 1) het bestaan uit 11 ramme en 11 ooie wat geoes was uit ‘n semi-ekstensiewe produksiestelsel in die Sentrale Sanderige Bosveld area naby Modimolle in die Limpopo provinsie van Suid-Afrika. Geen geslagsverskille (P > 0.05) was gevind vir die intakte karkasgewigte (36.4 ± 1.30 kg vir ramme; 37.8 ± 1.30 kg vir ooie) of karkasgewigte (21.6 ± 0.82 kg vir ramme; 21.0 ± 0.82 kg vir ooie) van rooibokke nie. Manlike rooibokke het egter ‘n hoër gemiddelde uitslagpersentasie as vroulike rooibokke getoon (59.1 ± 0.76 % teenoor 55.6 ± 0.76 %). Vir die produksiestelsel vergelyking (Eksperiment 2) was 12 sub-volwasse (±15-18 maande oud) rooibok ramme geoes per produksistelsel (n = 36), met beide die intensiewe en semi-ekstensiewe produksiesisteme naby Modimolle geleë en die ekstensiewe produksiestelsel geleë in die sentrale rûens skalie Renosterveld naby Bredasdorp in die Wes-Kaap provinsie van Suid-Afrika. Ekstensiewe rooibokke het hoër (P ≤ 0.05) intakte karkasgewigte en karkasgewigte (46.5 ± 1.12 kg en 26.6 ± 0.79 kg) as intensiewe (37.9 ± 0.92 kg en 21.9 ± 0.65 kg) en semi-ekstensiewe rooibokke (36.4 ± 0.96 kg en 21.3 ± 0.68 kg, onderskeidelik) gehad, terwyl die laasgenoemde twee sisteme se rooibokke nie betekenisvol van mekaar verskil het nie. Daar was ook geen verskille (P = 0.364) tussen die drie produksiestelsels vir die uitslagpersentasies (57.9 ± 0.58 % saamgestelde gemiddeld) of totale afval opbrengste (39.7 ± 0.48 % saamgestelde gemiddeld) van sub-volwasse rooibok ramme nie. Die fisiese vleiskwaliteitseienskappe van rooibokke was betekenisvol beïnvloed deur geslag, spier, en produksiesisteem. Betekenisvolle interaksies was gevind tussen geslag en spier vir die CIE a* waardes, drupverlies en kookverlies persentasies (Eksperiment 1). Rooibok ramme het hoër (P = 0.021) finale pH (pHu) waardes en laer (P = 0.002) Warner-Bratzler skeurkrag waardes gehad as ooie. Die IS en SS spiere van die voorkwart was die sagste in beide geslagte, terwyl die BF en SM spiere vanaf die agterkwart die taaiste was. Alhoewel die pHu waardes van beide geslagte, alle spiere (Eksperiment 1) en beide die intensiewe en semi-ekstensiewe rooibokke (Eksperiment 2) binne die normale omvang geval het (5.6-5.9), het rooibokke vanaf die ekstensiewe produksiestelsel vleis produseer met buitengewone hoë pHu waardes (6.2 ± 0.06) as gevolg van ekstrinsieke faktore veroorsaak deur die produksie- en oesproses. Die vleis van ekstensief geproduseerde rooibokke het gevolglik DFD-kenmerke (donker, ferm, droog) getoon, insluitend die laagste drupverliespersentasie (0.9 ± 0.14 %), kookverliespersentasie (28.1 ± 0.79 %) en die donkerste, minder rooi en minder versadigde oppervlakkleur (L* = 26.8; a* = 10.0; b* = 5.2; chroma = 11.4). Met die uitsondering van die ekstensief geproduseerde rooibokke, was die CIE oppervlakkleurmates van rooibokvleis van beide geslagte, alle spiere, en beide die intensiewe en semi-ekstensiewe produksiestelsels (L* = 30.9-36.8; a* = 11.4-13.6; b* = 6.0-8.8) binne die verwagte omvang wat as aanvaarbar geag word vir wildsvleis. Daarbenewens was all vars rooibokvleis in hierdie studie (Eksperiment 1 & 2) se skeurkragwaardes (19.2-39.3 N) laer as die 43 N afsnypunt en kan dus as sag geklassifiseer word. Die chemiese vleiskwaliteit van rooibokvleis was ook betekenisvol deur geslag, spier en produksiestelsel beïnvloed. Interaksies tussen geslag en spier was vir al vier chemiese eienskappe (vog-, proteïen-, intramuskulêre vet- (IMF), en asinhoud) gevind, terwyl ‘n sterk negatiewe korrelasie (r = -0.49; P < 0.001) tussen die proteïen- en IMF-inhoud van die spiere gevind was (Eksperiment 1). Ekstensief geproduseerde rooibokke se LTL spiere het die laagste (P ≤ 0.05) gemiddelde IMF-inhoud (1.5 ± 0.06 g/100 g) en die hoogste proteïen-inhoud (23.4 ± 0.12 g/100 g) gehad, terwyl rooibokke vanaf die intensiewe produksiestelsel die hoogste IMF-inhoud (2.0 ± 0.05 g/100 g) gehad het. Die proksimale samestelling van alle rooibokvleis in hierdie studie (Eksperiment 1 & 2) het gewissel van 74.7-77.0 % vog-, 20.7-23.5 % proteïen-, 1.2-2.2 % IMF- and 1.1-1.3 % asinhoud. Terwyl daar betekenisvolle verskille tussen geslag, spiere en produksiestelsels was, was die verskille numeries klein en mag dus nie van biologiese waarde tot menslike voeding wees nie. Ongeag hiervan het alle rooibokvleis in hierdie studie ‘n hoë proteïen- en lae IMF-inhoud gehad wat as gunstig deur gesondheidsbewuste verbruikers beskou word. Met die verskille in voeding, bestuurspraktyke en daaglikse aktiwiteit tussen produksiestelsels, kan daar verwag word dat hierdie faktore ook verskille in die sensoriese profiel en versuursamestelling van rooiblokvleis kan veroorsaak. Produksiestelsel het die sensoriese vleiskwaliteit van rooibokke beduidend beïnvloed (Eksperiment 2), met die hoogste (P ≤ 0.05) intensiteit van wilde, bees-agtige, kruid-agtige, en soet-geassosiëerde aromas en geure gevind in ekstensief geproduseerde rooibokvleis tydens sensoriese analise. In teenstelling met ekstensiewe rooibokke, het rooibokvleis vanaf beide die intensiewe en semi-ekstensiewe produksiestelsels in dieselfde produksie area nie beduidend verskil nie, met die uitsondering van ‘n paar tekstuur-verwante eienskappe en ‘n betekenisvolle hoër intensiteit vir wildsgeur wat in semi-ekstensief geproduseerde rooibokke gevind is. Die ideale vleisverouderingstydperk vir LTL snitte van rooibokke was ook deur hierdie navorsing vasgestel. Die LTL spiere van 11 rooibok ramme en 11 ooie (Eksperiment 1) was opgedeel in agt snitte elk, met elke LTL snit lukraak ingedeel om vir 1, 2, 4, 6, 8, 10, 12, of 14 dae the verouder, vakuum-verpak en gestoor teen 4°C. Hierdie studie het bepaal dat die maksimum sagtheid (13.5 ± 0.91 N) en verbetering in oppervlakkleur van rooibok LTL snitte teen agt dae behaal is, terwyl verdere veroudering van die vleis verkleuring veroorsaak het en geen verdere verbetering in sagtheid getoon het nie. Die veroudering van rooibokvleis vir agt dae het ook die aanvanklike betekenisvolle verskille in taaiheid tussen geslagte uitgeskakel. Dit word daarom aanbeveel dat rooibok LTL snitte vir agt dae vacuum-verouder moet word teen 4°C om maksimum sagtheid te behaal en ook produkunivormheid te verbeter deur verskille tussen individuele diere te verminder, ongeag hul geslag.

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