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

[摘要] ENGLISH ABSTRACT: The aim of this research was to investigate the influence of sex, muscle (Longissimus thoracis etlumborum/LTL, biceps femoris/BF, semimembranosus/SM, semitendinosus/ST, infraspinatus/IS, andsupraspinatus/SS), production system (intensive, semi-extensive and extensive), and post-mortemageing on the meat quality of impala (Aepyceros melampus) to provide baseline data for the SouthAfrican 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 asinvestigating 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 wereculled from a semi-extensive production system in the Central Sandy Bushveld region near Modimollein 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 ± 0.82kg 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 semiextensiveproduction systems were also located near Modimolle, and the extensive production systemwas located in the Central Rûens Shale Renosterveld region near Bredasdorp in the Western Cape ofSouth 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 semiextensivesystem impala (36.4 ± 0.96 kg and 21.3 ± 0.68 kg, respectively), while the latter two systemsdid not differ significantly from each other. No differences (P = 0.364) were recorded betweenproduction 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 losspercentages and cooking loss percentages (Trial 1). Higher (P = 0.021) ultimate pH (pHu) values andlower (P = 0.002) Warner-Bratzler shear force (WBSF) values were recorded in male impala than infemales. The IS and SS muscles from the forequarter were the most tender, whereas the BF and SMmuscles from the hindquarter were the least tender. The pHu of both sexes, all muscles (Trial 1) andboth 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) dueto extrinsic factors caused by the production and culling process. Consequently, extensive systemimpala produced meat with DFD-like (dark, firm, dry) characteristics, such as the lowest drip losspercentage (0.9 ± 0.14 %), cooking loss percentage (28.1 ± 0.79 %) and darkest, least red and leastsaturated surface colour (L* = 26.8; a* = 10.0; b* = 5.2; chroma = 11.4). With the exception of theextensive system impala, impala from both sexes, all muscles and both the intensive and semiextensivesystems (Trial 1 & 2) had CIE Lab colour measurements within the acceptable range ofexpectation for game meat (L* = 30.9-36.8; a* = 11.4-13.6; b* = 6.0-8.8). Furthermore, all fresh impalameat 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 andproduction 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) wasobserved between the protein and IMF content of the muscles (Trial 1). Extensively produced impalawere recorded to have LTL muscles with the lowest (P ≤ 0.05) mean IMF (1.5 ± 0.06 g/100 g) and thehighest protein (23.4 ± 0.12 g/100 g) content, whereas intensive system impala had the highest IMFcontent (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 % ashcontent. While the differences between sex, muscle and production system were significant, thedifferences were marginal and thus may not be of biological consequence with regards to humannutrition. Regardless, all impala meat had a high protein and low IMF content which is considereddesirable by health-conscious consumers.With the differences in dietary regime, management strategies and daily activity betweenproduction systems, it can be expected that the sensory profile and fatty acid composition of impalameat will also be influenced by differences in these factors. The influence of production system onsensory 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 impaladuring descriptive sensory analysis (DSA). However, the sensory meat quality of the intensive andsemi-extensive system impala from the same production region did not differ (P > 0.05) except for afew textural attributes and a higher (P < 0.05) gamey flavour intensity found in semi-extensive systemimpala. The ideal post-mortem ageing period of impala LTL steaks was also determined. The LTLmuscles of 11 male and 11 female impala (Trial 1) were divided into eight portions each, with eachportion was randomly allocated to age for 1, 2, 4, 6, 8, 10, 12, or 14 days, vacuum-sealed and storedat 4°C. This research found that maximum tenderness (13.5 ± 0.91 N) and improvement of bloomedsurface colour of impala LTL steaks was reached at eight days post-mortem, whereas prolongedageing beyond this point resulted in some discolouration and no further improvement in meattenderness. The ageing of meat to eight days post-mortem also successfully negated the initialsignificant differences in tenderness between the sexes. Therefore, it is recommended that impala LTLsteaks should be vacuum-aged at 4°C for eight days to achieve optimum tenderness and minimizevariability between individual animals irrespective of sex.

[发布机构] Stellenbosch University