Meat quality of Nguni, Bonsmara and Aberdeen Angus steers raised on natural pasture in the Eastern Cape, South Africa

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MEAT SCIENCE Meat Science 79 (2008) 20–28 www.elsevier.com/locate/meatsci

Meat quality of Nguni, Bonsmara and Aberdeen Angus steers raised on natural pasture in the Eastern Cape, South Africa V. Muchenje b

a,b

, K. Dzama c, M. Chimonyo

a,*

, J.G. Raats a, P.E. Strydom

d

a Department of Livestock and Pasture Science, University Of Fort Hare, Post Bag X1314, Alice 5700, South Africa Department of Agriculture Management, Zimbabwe Open University, Bulawayo Region, P.O. Box 3550, Bulawayo, Zimbabwe c Department of Animal Sciences, Stellenbosch University, Post Bag X1, Matieland 7602, South Africa d Agricultural Research Council, Department Nutrition and Food Science, Private Bag X2, Irene 0062, South Africa

Received 14 December 2006; received in revised form 25 June 2007; accepted 23 July 2007

Abstract The current study compared meat quality of Nguni, Bonsmara and Angus steers raised on natural pasture. Fifteen seven-month-old weaners of each breed were kept at the University of Fort Hare Farm for 12 months till slaughter. Monthly weights of the steers were recorded. Carcasses were electrically stimulated. The m. longissimus thoracis et lumborum was sampled for the measurement of meat colour, pH, drip loss, sarcomere length, myofibrillar fragmentation length and Warner Bratzler (WB) shear force. The Nguni had the highest (P < 0.05) average daily gain. Bonsmara and Angus steers had higher (P < 0.05) carcass weight and dressing percentage than the Nguni steers. Meat quality characteristics were similar among all the breeds except that Nguni meat was darker (L*) (P < 0.05) than meat from the other two breeds. The respective L* values for Nguni, Bonsmara and Angus steers were 36.5, 38.6 and 39.9. There were significant (P < 0.05) correlations among some meat quality traits. There were significant (P < 0.05) correlations between WB values of meat aged for 2 and 21 days in Nguni and Bonsmara, but not in Angus. Meat quality from Nguni compares favourably with that from established breeds, when raised on natural pasture.  2007 Elsevier Ltd. All rights reserved. Keywords: Meat quality; Natural pasture; Natural meat; Nguni cattle

1. Introduction With consumers becoming increasingly concerned about meat eating quality, they also require information on the origin of meat and the production system used (Revilla & Vivar-Quintana, 2006). As a way of encouraging production systems that conform to consumer demands, there is a promotion for the use of the adapted indigenous Nguni cattle breed for beef production in the rural areas of South Africa. In rural areas, there are limited and inadequate veld management practices, resulting in overgrazing, overstocking and loss of weight, especially

*

Corresponding author. Tel.: +27 40 602 2101; fax: +27 40 653 1730. E-mail address: [email protected] (M. Chimonyo).

0309-1740/$ - see front matter  2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2007.07.026

during the dry season (Bester, Matjuda, Rust, & Fourie, 2003), which ultimately is likely to affect meat yield and quality. Despite these possible limitations, the promotion of Nguni beef production in rural areas can increase offtake and reduce beef imports in South Africa where local meat supply cannot meet the demand for meat products. Nguni cattle possess several attributes, such as resistance to ticks and tick-borne diseases, high reproductive performance, good walking and foraging ability, and low maintenance requirements, acquired through centuries of natural selection (Collins-Luswet, 2000; Strydom, Naude, Smith, Scholtz, & van Wyk, 2000, 2001). European breeds, such as the Aberdeen Angus, Hereford and Simmental which have been developed under relatively benign conditions, fail to survive under veld conditions where the Nguni thrives.

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Although it is established that breed and feeding management influence the quality of meat (Andersen, Oksbjerg, Young, & Therkildsen, 2005; San˜udo et al., 2004; Wheeler, Cundiff, Koch, & Crouse, 1996), no information is available on the meat quality of Nguni cattle raised on natural pasture without dietary supplementation, as is practiced in rural areas. There is a need to evaluate meat quality of the Nguni cattle under conditions that mimic rural conditions and management systems. Although feed quantity and quality is adequate during the rainy season, biomass yield declines during the dry season, resulting in cattle losing weight. To counter the need for dietary supplementation, farmers sell their animals for slaughter before marked weight losses begin. There is, therefore, need to evaluate meat quality from these indigenous Nguni cattle under rural management conditions on natural pasture. Most studies on meat quality on the Nguni cattle have been on feedlot systems under commercial farming conditions (Gertenbach & Henning, 1995; Strydom et al., 2000, 2001). There are conflicting reports on the effect of feeding management on meat quality (Priolo, Micol, & Agabriel, 2001). For example, Vestergaard, Oksbjerg, and Henckel (2000) and Baublits et al. (2004) reported that forage-fed beef has less marbling and darker lean colour than grainfed beef. However, Bidner, Schupp, Montgomery, and Carpenter (1981) reported no differences in quality grades and marbling scores between carcasses from forage-fed and maize-supplemented forage steers. There are various reports on relationships among meat quality traits. For example meat tenderness is related to ultimate pH (pHu) value and meat colour (Byrne, Troy, & Buckley, 2000; Strydom et al., 2000; Vestergaard et al., 2000). However, no reports are available that compare these relationships within the Nguni breed raised on natural pasture. The colour of meat and external fat of cuts of meat influences the purchasing willingness and visual consumer acceptability. The objective of the study was to compare productive performance and meat quality characteristics of Nguni meat versus Bonsmara and Aberdeen Angus when raised on natural pasture. Correlations among meat quality within breeds were also estimated. The hypothesis tested was that, under natural grazing, meat from Nguni steers is similar to meat from the Bonsmara and Angus breeds. 2. Materials and methods 2.1. Site description The study was conducted at Honeydale Farm, University of Fort Hare. The farm is 520 m above sea level and is located 32.8 latitude and 26.9 longitude. It is situated in the False Thornveld of the Eastern Cape, with an average annual rainfall of 480 mm. Most of the rainfall comes in summer. The mean annual temperature of the farm is 18.7 C. The vegetation is composed of several trees, shrubs and grass species. Acacia karroo, Themeda triandra, Panicum maximum, Digitaria eriantha, Eragrostis spp.,

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Cynodon dactylon and Pennisetum clandestinum are the dominant plant species. The topography of the area is generally flat with a few steep slopes. 2.2. Animal management, handling and slaughter procedure Fifteen steers each of Nguni, Bonsmara and Angus weaners of similar age (around 205 days) were used in the current study. They were raised from April 2005 till slaughter at 19 months of age. The animals rotationally grazed on natural pasture. To simulate communal grazing systems, the natural pastures had the original tree and grass species and had never been disturbed in terms of ploughing, reinforcement or any other land manipulation except being used for grazing. The steers were never given any dietary supplementation. In the study area, the pasture was lush from the end of October to the beginning of January. The quantities of grass began to decline from March and were at the lowest around August and September. The slaughter date was chosen to coincide with the beginning of the decline in the quantity of grasses in the pasture. The steers were dipped using a commercial acaricide after every 2 weeks to control ticks. The animals were not kraaled at night. Monthly weights of all animals were recorded to compute growth rates of the steers. Average daily gain (ADG) (g/day) between weaning (initial weight) and slaughter (slaughter weight) was calculated. On the day prior to slaughter, the animals were weighed off-pasture and were kept overnight at the abattoir holding pens without food. Water was available at all times. Animal slaughter and dressing was done following usual commercial procedures at the East London Abattoir. The captive bolt method was used to stun the animals. Carcasses were electrically stimulated, using a voltage of 300 V, a frequency of 50 Hz, a current of 5 A in 40–45 s at a pulse of 12/s, to control the effect of rapid chilling on cold shortening of muscles. The dressed carcass comprised the body after removing the skin, the head at the occipito-atlantal joint, the fore-feet at the carpal–metacarpal joint, the hind feet at the tarsal–metatarsal joint and the viscera. Warm carcass weight, conformation and carcass classification grades were recorded. The grade classification used in South Africa considers age (A = 0 teeth, AB = 1–2 teeth, B = 3–6 teeth, and C = more than 6 teeth) and fatness (fatness scale 0–6, with 0 = no visual fat cover, 1 = very lean, 2 = lean, 3 = medium, 4 = fat, 5 = overfat, and 6 = excessively overfat). The South African meat industry uses a conformation scale of 1–5 (with 1 = a very flat carcass, 2 = a flat carcass, 3 = medium carcass, 4 = a round carcass, and 5 = a very round carcass). The dressing out percentage was calculated as warm carcass weight expressed as a percentage of the liveweight. Carcasses were split, weighed and then chilled at 0–3 C before being processed the following day after slaughter. Location of sampling was precise in order to limit the effect of muscle sampling site on any characteristic. The m. longissimus thoracis et lumborum (LTL) of the left side was

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sampled, a day after slaughter, from the 10th rib in the direction of the rump in the following order and amounts for meat quality analyses: (a) 100 mm thick for 2-day aged Warner Bratzler test, (b) 100 mm thick for 21-day aged Warner Bratzler tests, (c) a 20 mm steak for myofibrillar length on 2-day aged sample, (d) a 20 mm steak for myofibrillar length on 21-day aged sample, (e) a 10 mm steak for sarcomere length, (f) a 15 mm steak for drip loss in duplicate, (g) a 20 mm steak for CIE Lab colour measurement. This amounted to approximately 2.5 kg meat sample per animal. All the meat quality analyses were done on the LTL. 2.3. Meat quality measurements 2.3.1. pH and drip loss measurement A pH meter was used to measure pHu of the LTL 24 h post-mortem. For drip loss measurement, two blocks of meat measuring 15 · 15 · 30 mm were sliced from the LTL steak so that the fibres ran across the longer axis of the sample. The samples were suspended on metal hooks in plastic sample bottles so that the sample did not touch the side of the bottle. The suspended samples were stored in a cool room at 2 C for 72 h and the drip loss calculated as the differences between the initial and final weight of the sample expressed as a percentage. 2.3.2. Sarcomere length determination For determination of sarcomere length, portions of about 20 g were cut from the core of the frozen samples and prepared according to Hegarty and Naude´ (1970) as modified by Dreyer, Van Rensburg, Naude´, Gouws, and Stiemie (1979). The frozen samples were homogenised using distilled water (Dreyer et al., 1979). A few droplets of the homogenate were mounted on a slide, covered with a cover slip and immediately viewed under a microscope attached to a video image analyser (VIA; Kontron Germany), at a magnification of 100·. One hundred randomly selected fibres were selected. The length of five consecutive sarcomeres was recorded per selected fibre, to improve the accuracy of the measurement. The recorded value was then divided by five and the final sarcomere length was the average length of 100 measurements. 2.3.3. Myofibrillar fragment length determination Two samples, each weighing approximately 50 g, of the LTL were taken for myofibrillar fragment length (MFL) measurement, which indicates fragmentation due to postmortem proteolysis (determination of aging rate over 21 days). The samples were vacuum packed and aged for 2 and 21 days at 3 C, and were prepared for MFL. The MFL was determined by the method of Culler, Parrish,

Smith, and Cross (1978) as modified by Heinze and Bruggemann (1994). The methods involved the extraction of the myofibres in the buffer solution at around 4 C to arrest any further proteolysis. Droplets of the extracted MFL solution were mounted on a slide, covered and viewed at a magnification of 40x under a microscope attached to the VIA. The MFL was determined as the average length of the first 50 myofibrills that were longer than five sarcomeres. 2.3.4. Determination of chemical composition and colour A 50 g sample of the LTL was ground and freeze dried for the determination of protein, fat, moisture and ash contents (AOAC, 1985). The fat content reflected the degree of marbling in the muscle. Muscle colour was measured with a minoltameter (Model CR200, Minolta, Japan) on fresh unaged samples (2 days post-mortem). A 30 g portion of the LTL was cut, wrapped in oxygen permeable polythene film, and left to bloom for 30 min at 3 C before colour determination. The minoltameter was standardised against a white calibration tile that was wrapped in the same polythene cling film used for the meat samples. The Commission Internationale De L’Eclairage (CIE) L*, a* and b* values (Commission International De I’ Eclairage, 1976) were determined on the cut surface. Three replicate measurements, which avoided areas of connective tissue and intramuscular fat, were taken per sample. Colour saturation was calculated as the square root of the sum of a*2 and b*2. 2.3.5. Warner Bratzler shear force determination The sampled LTL to be used for shear force resistance were vacuum packed and either frozen directly (for those aged for 2 days) or aged at 2 C for a further 19 days after processing (21 days in total) and frozen. Two days before preparation, three steaks measuring 30 mm thick were cut with a band saw, vacuum packed and thawed over 24 h at 0–4 C. The steaks were prepared according to an oven-broiling method using direct radiant heat (AMSA, 1978). An electric oven was set on ‘‘broil’’ 10 min prior to preparation at 260 C. Steaks were placed on an oven pan on a rack to allow meat juices to drain during cooking and placed in the pre-heated oven 90 mm below the heat source. The steaks were cooked to an internal temperature of 35 C recorded by direct probe, then turned and finished to 70 C. Raw and cooked weights were recorded. Following cooking, the steaks were cooled at room temperature for 5 h before shear force determination. Eight sub samples measuring 2.5 mm core diameter were cored parallel to the grain of the meat, and sheared perpendicular to the fibre direction using a Warner Bratzler (WB) shear device mounted on an Universal Instron apparatus (cross head speed = 400 mm/min, one shear in the centre of each core). The mean maximum load recorded for the eight cores represented the average of the peak force in Newtons (N) of each sample.

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2.4. Statistical analysis The effects of breed on productive performance and meat quality traits, and the effects of aging on WB and MFL were analysed using Generalised Linear Models procedures of SAS (2000). The significance differences between least square group means were compared using the PDIFF test of SAS (2000). Pearson’s correlation coefficients among meat quality traits in all steers and within breeds were also determined (SAS, 2000). 3. Results and discussion 3.1. Productive performance of steers Liveweight, average daily gain and carcass characteristics of the three breeds are presented in Table 1. There were significant breed effects in liveweight, with the Nguni being lighter (P < 0.05) than the Aberdeen Angus and the Bonsmara. However, the Nguni had a higher (P < 0.05) daily gain from weaning to slaughter than the other two breeds. It also had a lower (P < 0.05) daily loss when veld condition was poor, which demonstrates the Nguni’s ability to perform better than the bigger breeds under natural pasture, particularly if the quality of grazing is low, as is the case in the dry season in the rural areas. The loss of weight in the steers from March till slaughter in April can be ascribed to the poor rainfall that was recorded in the month of March. The total rainfall in March 2006 during the study was 20.8 mm while the 37-year mean for the study site is 70.3 mm. As expected, carcass weights followed a similar trend to slaughter weights. Nguni steers had lighter (P < 0.05) carcasses than the two large-framed breeds. The dressing percentage was similar (P < 0.05) between the Nguni and the Aberdeen Angus but lower (P < 0.05) than in the Bonsmara. This could be due to heavier hairy skins in the Angus and presence of horns in the Nguni steers. The presence of horns in Nguni steers was as a result of absence of dehorning, as recommended by the Nguni stud

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breeders and suppliers (Hobbs, 2005). Dual-purpose breeds have been reported to have lower dressing percentage than pure beef breeds because coefficients of growth for non-carcass fat are higher than those for carcass fat (Kempster, Chawick, & Charles, 1982; Keane, More O’Ferrall, Conolly, & Allen, 1990; King et al., 2006). This explanation can be applicable to the Nguni, a multipurpose breed, although it does not adequately explain the low dressing percentage in the Aberdeen Angus. Purchas, Banton, and Hunt (1992) found that carcasses from large framed and late maturing breeds have less fat, higher conformation scores, dressing percentage and proportion of first category cuts. The carcass age-fat classes of the three breeds were similar (P > 0.05). Although management measures to improve the natural pasture, such as rotational grazing, were undertaken in the current study, deterioration of grazing lands in the dry season usually occurs in rural areas. The steers were generally thin because of the poor condition of the veld that had deteriorated from March due to poor rainfall. Thirty one of the carcasses were classified as A0 and six carcasses were classified as A1 (A – no permanent incisors, scale 0–6 with 0 representing no visual fat cover and 6 representing excessively overfat). On a conformation scale of 1–5 (with 1 representing a very flat carcass and 5 representing a very round carcass), more (P < 0.01) carcasses were classified as 3 than those classified as 2 (Table 2). The conformation for the Nguni carcasses was poorer (P < 0.01) than that of the other two breeds. The poorer conformation for the Nguni carcasses than that of the other two breeds was expected since bigger breeds tend to have better carcass conformation than smaller breeds. Continental meat breeds generally have better conformation than traditional breeds (Alberti et al., 2005; Purchas et al., 1992; Vieira, Cerdeno, Serrano, Lavin, & Mantecon, 2006). Continental meat breeds have been selected for meat production over a long period. Although it is an indicator of potential meat yield, carcass conformation is, however, not critical in carcass grading in South Africa.

Table 1 Least square means and standard errors of means (in parentheses) for productive performance of Nguni, Bonsmara and Aberdeen Angus steers Trait

Breed

Significance

Nguni

Bonsmara

Aberdeen Angus

Gain 1 (g/day) Gain 2 (g/day) Weight loss (g/day) March weight (kg) Slaughter weight (kg) Warm carcass weight (kg) Dressing percentage (%)

98 (13.7)a 198 (15.8) 566 (7.10)a 237 (6.8)a 205 (6.5)a 107 (3.5)a 52.1 (0.75)a

28 (14.2)b 183 (16.4) 991 (69.6)b 311 (7.0)b 255 (6.8)b 145 (3.7)b 56.9 (0.78)b

44 (16.9)b 198 (19.4) 872 (82.5)b 288 (8.3)b 240 (8.0)b 129 (4.4)c 53.7 (0.92)a

*

NS * * * * *

Means in the same column with different superscripts are significantly different (P < 0.05). Gain 1 = the difference between the slaughter weight and the weaning weight divided by the number of days from weaning to slaughter. Gain 2 = the difference between the March 2006 weight and weaning weight divided by the number of days from weaning to March 2006. Weight loss = the difference between the slaughter weight and the March 2006 weight divided by the number of days from March 2006 to slaughter.

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Table 2 Frequency of carcass conformation classes in Nguni, Bonsmara and Aberdeen Angus steers Breed

Frequency (%) conformation class

Aberdeen Angus Bonsmara Nguni Total

10.3 5.1 28.2 43.6

2

Total

P-value

25.6 (10) 35.9 (14) 38.5 (15) 100 (39)

0.0057

3 (4) (2) (11) (17)

15.4 30.8 10.3 56.4

(6) (12) (4) (22)

Values in parentheses indicate the number of cases.

3.2. Meat quality Besides meat lightness (L*) and chemical composition, most meat quality characteristics among the three breeds were similar (P < 0.05) (Table 3). The L* value for Nguni meat was lower (P < 0.05) than that of the other two breeds. The appearance characteristics, except lightness L*, were similar in the three breeds, which agrees with Muir, Wallace, Dobbie, and Bown (2000), Chambaz, Scheeder, Kreuzer, and Dufey (2003), and Revilla and Vivar-Quintana (2006). It is important to note that although L* for Nguni meat was lower than the Bonsmara and Angus meat, a difference of less than three units is, practically, quite small. Differences in meat colour have been associated with variations in intramuscular fat and moisture content, age dependent changes in muscle myoglobin content (Lawrie, 1974), the pHu of the muscle (Hector, Brew-Graves, Hassen, & Ledward, 1992), with higher pHu being associated with dark cuts and vice versa. However, Priolo et al. (2001) concluded that the evidence on the Table 3 Least square means and standard errors of means (in parentheses) of meat quality characteristics of Nguni, Bonsmara and Aberdeen Angus steers Breed

N Lightness (L*) Redness (a*) Yellowness (b*) Colour saturation Sarcomere length (lm) WB2 (N) WB21 (N) MFL2 (lm) MFL21 (lm) pH Drip loss (%) Moisture (%) Ash (%) Protein content (%) Fat content (%)

Nguni

Bonsmara

Aberdeen Angus

15 36.5 (0.50)a 15.8 (0.38) 6.5 (0.20) 17.1 (0.42) 1.6 (0.02) 39.2 (3.72) 33.3 (2.74) 26.2 (0.94) 20.9 (0.61) 5.7 (0.02) 1.8 (0.12) 77.1 (0.12)a 1.10 (0.006)a 21.0 (0.12)a 0.87 (0.073)

14 38.6 (0.52)b 16.0 (0.39) 6.7 (0.21) 17.4 (0.43) 1.7 (0.03) 46.1 (3.82) 34.3 (2.84) 27.4 (0.97) 19.6 (0.63) 5.7 (0.03) 1.6 (0.13) 77.6 (0.13)b 1.07 (0.007)b 20.6 (0.12)b 0.79 (0.077)

10 39.9 (0.62)b 16.6 (0.47) 7.1 (0.25) 18.1 (0.51) 1.6 (0.03) 37.2 (4.51) 35.3 (3.33) 27.6 (1.15) 19.2 (0.74) 5.7 (0.03) 1.7 (0.15) 77.9 (0.15)b 1.07 (0.010)b 20.0 (0.14)c 0.76 (0.092)

Means in the same row with different superscripts are significantly different at P < 0.05; MFL2 – Myofibrillar fragment length for meat aged for 2 days; MFL21 – Myofibrillar fragment length for meat aged for 21 days; WB2 – Warner Bratzler value for meat aged for 2 days; WB21 – Warner Bratzler value for meat aged for 21 days.

causes of variation was mixed. In this study, there were poor correlations between L* and percentage moisture, and between L* and pHu. In addition, the steers used in the current study were of similar age and had similar intramuscular fat. The darker meat produced by the Nguni steers in comparison to the improved breeds agrees with O’Neill, Webb, Frylinck, and Strydom (2006). Differences in meat colour are not fully understood. O’Neill et al. (2006), however, observed that Nguni cattle released more catecholamines than European breeds, during the preslaughter period, causing the depletion of glycogen. Glycogen depletion lowers glycogen levels, resulting in an increase in pHu, which is not optimal for the conversion of muscle into meat (O’Neill et al., 2006; Purchas, Yan, & Hartly, 1999). An increase in pHu does not necessarily result in tougher meat as other parameters with regard to meat tenderness may be involved. As shown in Table 3, the pHu (<6.2) and L* values (>33) were within the expected ranges (Lawrie, 1974; Diaz, Anaya, Gonzalez, Sanchez-Escalante, & Torrescano, 2006) that would not result in dark firm dry (DFD) meat. The WB values, MFL and sarcomere lengths were similar (P < 0.05) among the breeds, which agrees with Muir et al. (2000) and Revilla and Vivar-Quintana (2006) in which the tenderness of meat from steers of different breeds was similar when slaughtered at the same age. Strydom et al. (2000, 2001) also reported no differences in WB values among Nguni and Bonsmara steers raised in a feedlot. San˜udo et al. (2004), however, reported that differences between breed types for most WB values were more pronounced at the lower carcass weight than at higher carcass weights. It has also been reported that different breeds had a wide spectrum of fibre types in muscles, but these were not always reflected by differences in instrumental analyses using WB or sensory panels (San˜udo et al., 2004). Meat tenderness significantly (P < 0.05) improved with aging of the muscle. However, in the Angus steers meat, there was no difference (P < 0.05) in WB values after aging for 2 and 21 days, possibly due to almost complete aging of the Angus meat by day 2. Meat tenderness is a function of the collagen content, heat stability and the myofibrillar structure of muscle, though these appear to be affected mainly by the rate of growth of the cattle rather than breed per se (Muir et al., 2000; Monso´n, San˜udo, & Sierra, 2005). The myofibrillar component of tenderness can also be influenced by the calpain proteolytic enzyme system during aging of the carcass post-mortem. Wheeler and Koohmaraie (1991) suggested that the myofibrillar component could be a more important factor than the connective tissue characteristics in influencing meat tenderness. This could be applicable in this study where the animals were slaughtered at a young age implying that the muscles were likely to be low in connective tissue. The chemical composition of meat significantly differed (P < 0.05) among the three breeds. Moisture content was lower in Nguni carcasses than in the other two breeds. Intramuscular fat was similar among the three breeds,

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WB values. As expected, there were significant (P < 0.05) negative correlations between sarcomere lengths and WB values within the Nguni and Bonsmara steers. The negative correlation between sarcomere lengths and WB values can be attributed to the fact that muscles with short sarcomere length are generally tough (Strydom et al., 2000; Revilla & Vivar-Quintana, 2006). As expected, there was a positive correlation between WB shear force values and MFL values in Nguni and Bonsmara steers. This can be ascribed to the fact that meat tenderness is a function of the collagen content and the myofibrillar structure of muscle (Muir et al., 2000; Revilla & Vivar-Quintana, 2006). The correlation between WB values and collagen was, however, not determined in the current study. Furthermore, the variation in WB values depend more on the myofibrillar content than the total collagen content or its solubility, especially if it is considered that the shear force on cooked meat may also be a measure of myofibrillar toughness (San˜udo et al., 2004). Strydom et al. (2000) reported significant within-breed correlations between myofibrillar fragmentation index (MFI) and ten-

which agrees with Strydom et al. (2001), but lower than the fat content reported in Limousin and Charolais young bulls (Revilla & Vivar-Quintana, 2006). There were breed effects on protein content of beef, with Nguni carcasses having the highest protein content and the Angus steers having the least protein content. The pHu values, averaging 5.7, were within the expected range and similar to those reported by other authors (Beltran et al., 1997; Revilla & Vivar-Quintana, 2006; Silva, Patarata, & Martins, 1999). In agreement with previous reports (Chambaz et al., 2003; Hoving-Bolink, Hanekamp, & Wastra, 1999; Monson, San˜udo, & Sierra, 2004), no breed differences (P > 0.05) on pHu were observed in the current study. 3.3. Meat quality correlations As shown in Tables 4–7, most meat quality traits were not correlated (P < 0.05), especially in the Angus steers. Most significant (P < 0.05) correlations were among meat tenderness characteristics such as MFL, sarcomere and Table 4 Correlations among quality traits of meat from all steers pH Lightness (L*) pH Moisture Protein Fat Drip loss Sarcomere MFL2a MFL21b WB2c

0.31

Moisture 0.38* 0.43**

Protein

Fat

0.41** 0.32* 0.86***

0.30 0.05 0.36* 0.05

Sarcomere

MFL2a

MFL21b

0.17 0.21 0.25 0.23 0.01

0.26 0.11 0.23 0.23 0.20 0.42**

0.02 0.06 0.10 0.10 0.20 0.24 0.30

0.18 0.30 0.21 0.17 0.41* 0.28 0.21 0.26

Drip loss

Sarcomere

MFL2a

MFL21b

Drip loss

WB2c 0.21 0.12 0.16 0.19 0.03 0.62*** 0.47** 0.42** 0.34*

WB21d 0.18 0.15 0.22 0.21 0.08 0.78*** 0.58*** 0.43** 0.31 0.79***

Significantly correlated at *P < 0.05, **P < 0.01, ***P < 0.05. a Myofibrillar fragment length for meat aged for 2 days. b Myofibrillar fragment length for meat aged for 21 days. c Warner Bratzler value for meat aged for 2 days. d Warner Bratzler value for meat aged for 21 days.

Table 5 Correlations among quality traits of meat from Nguni steers pH Lightness (L*) pH Moisture Protein Fat Drip loss Sarcomere MFL2a MFL21b WB2c

0.30

Moisture 0.15 0.57*

Protein

Fat

0.25 0.35 0.89***

Significantly correlated at *P < 0.05, **P < 0.01, ***P < 0.05. a Myofibrillar fragment length for meat aged for 2 days. b Myofibrillar fragment length for meat aged for 21 days. c Warner Bratzler value for meat aged for 2 days. d Warner Bratzler value for meat aged for 21 days.

0.22 0.02 0.28 0.11

0.46 0.12 0.12 0.18 0.12

0.60* 0.12 0.50 0.54* 0.12 0.64**

0.31 0.24 0.50 0.65** 0.06 0.28 0.53*

0.22 0.06 0.41 0.49 0.05 0.39 0.39 0.25

WB2c 0.48 0.16 0.24 0.37 0.16 0.80*** 0.59* 0.48 0.26

WB21d 0.52* 0.19 0.44 0.54* 0.06 0.87*** 0.73** 0.52* 0.49 0.90***

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Table 6 Correlations among quality traits of meat from Bonsmara steers pH Lightness (L*) pH Moisture Protein Fat Drip loss Sarcomere MFL2a MFL21b WB2c

0.45

Moisture 0.20 0.44

Protein

Fat

0.02 0.63* 0.85***

Drip loss

0.29 0.17 0.55* 0.29

0.13 0.57* 0.54* 0.59* 0.17

Sarcomere 0.20 0.26 0.04 0.03 0.18 0.41

MFL2a

MFL21b

0.01 0.07 0.04 0.16 0.27 0.32 0.39

0.59* 0.46 0.09 0.13 0.52 0.23 0.57* 0.45

MFL2a

MFL21b

0.12 0.39 0.03 0.04 0.12 0.34 0.08

0.39 0.39 0.25 0.27 0.40 0.32 0.67* 0.27

WB2c 0.21 0.12 0.23 0.16 0.25 0.73** 0.78** 0.40 0.62*

WB21d 0.08 0.24 0.36 0.37 0.03 0.85*** 0.74** 0.36 0.41 0.82***

Significantly correlated at *P < 0.05, **P < 0.01, ***P < 0.05. a Myofibrillar fragment length for meat aged for 2 days. b Myofibrillar fragment length for meat aged for 21 days. c Warner Bratzler value for meat aged for 2 days. d Warner Bratzler value for meat aged for 21 days.

Table 7 Correlations among quality traits of meat from Aberdeen Angus steers pH Lightness (L*) pH Moisture Protein Fat Drip loss Sarcomere MFL2a MFL21b WB2c

0.42

Moisture

Protein

0.24 0.73*

0.15 0.47 0.72*

Fat

Drip loss

0.27 0.02 0.24 0.37

0.58 0.10 0.01 0.07 0.15

Sarcomere 0.18 0.24 0.49 0.45 0.29 0.04

WB2c 0.04 0.13 0.02 0.08 0.09 0.34 0.53 0.52 0.33

WB21d 0.18 0.59 0.45 0.12 0.37 0.40 0.23 0.47 0.05 0.08

Significantly correlated at *P < 0.05, **P < 0.01, ***P < 0.05. a Myofibrillar fragment length for meat aged for 2 days. b Myofibrillar fragment length for meat aged for 21 days. c Warner Bratzler value for meat aged for 2 days. d Warner Bratzler value for meat aged for 21 days.

derness. In Nguni and Bonsmara steers, meat with high WB shear force values after being aged for 2 days also had high WB shear force values after being aged for 21 days. In Angus steers, however, MFL, sarcomere and WB shear force values for meat aged for 2 days and the one aged for 21 days were not correlated (P < 0.05). The lack of a correlation between WB values of Angus steers meat aged for 2 days and the one aged for 21 days is unexpected. With the WB values of the Angus steers meat being more variable than the WB values of the Nguni and Bonsmara meat, significant correlations between the two variables in the Angus would be expected. The lack of correlations between WB shear values may be ascribed to the fact that aging in Angus steers meat was almost complete at 2 days; the respective WB shear force values of meat from Angus steers aged for 2 and 21 days were 37.2 N and 35.3 N. Beef crosses with more Angus blood were reported to age faster than those crosses with less Angus blood (Stolowski et al., 2006). There were significant (P < 0.05) correlations involving chemical composition traits, especially moisture and pro-

tein. Drip loss was negatively correlated (P < 0.05) to sarcomere length in the Nguni steers, but there was no relationship between drip loss and sarcomere length in Bonsmara and Angus steers. There was a significant positive correlation (P < 0.05) between drip loss and WB values within Nguni and Bonsmara steers. This implies that meat that loses more water is tougher than meat that loses less water. Drip loss and WB values were, however, not correlated in the Angus steers. While there were significant (P < 0.05) negative correlations between L* and protein, and positive correlations between L* and moisture across steers, such correlations were not found within individual breeds. According to Muir et al. (2000) and Revilla and Vivar-Quintana (2006), differences in meat colour are associated with the concentrations and oxidation state of myoglobin, and variations in intramuscular fat and moisture content. There were significant (P < 0.05) positive correlations between pHu and moisture in Nguni and Angus steers. There were no correlations (P < 0.05) between pHu and L*. However, higher pHu values tend to result in dark firm dry (DFD),

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although this does not necessarily mean that the meat will be tougher, as other parameters could be involved. The pHu (6.2) and L* values (>33) observed in the current study were within the expected ranges that would not result in DFD meat (Diaz et al., 2006; Lawrie, 1974). 4. Conclusions The Nguni steers had poorer conformation, higher ADG, lower carcass weight and dressing percentage than the other two breeds. Nguni steers had darker colour, higher dry matter and protein content than the Bonsmara and Angus steers. There were no differences in intramuscular fat among the three breeds. Meat tenderness from the three breeds improved with aging. Most meat quality traits were not correlated. However, there were significant correlations between moisture and protein content and most quality traits, and among meat tenderness characteristics such as MFL and WB values in Nguni and Bonsmara steers. It can be concluded that, under adverse conditions, which are common during the dry season in the rural areas of the Eastern Cape, Nguni meat quality was as good as meat quality from Angus and Bonsmara cattle breeds. Therefore, besides being a smaller and multipurpose breed the Nguni can compete favourably with established breeds in terms of productive performance and meat quality. There is need, however, to perform a sensory evaluation of the meat and assess other meat aspects, such as fatty acid profiles, against Angus and Bonsmara cattle breeds. Acknowledgements This research was funded by the Kellogg-Nguni Cattle Project. The steers were slaughtered at the East London Abattoir. The meat samples were analysed at the Agricultural Research Council (ARC) Meat Industry Centre at Irene, Pretoria. References Alberti, P., Ripolli, G., Goyache, F., Lahoz, F., Olleta, J. L., Panea, B., et al. (2005). Carcass characterization of seven Spanish beef breeds slaughtered at two commercial weights. Meat Science, 71, 514–521. Andersen, H. A., Oksbjerg, N., Young, J. F., & Therkildsen, M. (2005). Feeding and meat quality – a future approach. Meat Science, 70, 543–554. AOAC (1985). Official methods of analysis of the AOAC International (16th ed.). Washington, DC: Association of Official Analytical Chemists. AMSA (1978). Guidelines for cooking and sensory evaluation of meat. Chicago, IL: American Meat Science Association, National Livestock and Meat Board. Baublits, R. T., Brown, A. H., Pohlman, F. W., Johnson, Z. B., Onks, D. O., Loveday, H. D., et al. (2004). Carcass and beef colour characteristics of three biological types of cattle grazing cool-season forages supplemented with soyhulls. Meat Science, 68, 297–303. Beltran, J. A., Jaime, I., Santolaria, P., San˜udo, C., Alberti, P., & Roncales, P. (1997). Effects of stress-induced high post-mortem pH on protease activity and tenderness of beef. Meat Science, 45, 201–207.

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