Effect of South African beef production systems on post-mortem muscle energy status and meat quality

Post-slaughter muscle energy metabolism and meat colour of South African production systems were compared; steers (n=182) of Nguni, Simmental and Brahman crossbreds were reared on pasture until A-, AB-, or B-age, and in feedlot until A- and AB-age. After exsanguination carcasses were electrically stimulated (400 V for 15s); m. longissimus dorsi muscle energy samples were taken at 1, 2, 4 and 20 h post-mortem and samples for meat quality studies were taken at 1, 7 and 14 days post-mortem. Production systems affected muscle glycogen, glucose, glucose-6-P, lactic acid, ATP, creatine-P and glycolytic potential (P<0.05), with the muscles of feedlot carcasses having faster glycolysis rate than pasture carcasses. Energy metabolites correlated (0.4<r<0.9) with meat colour (CIE, L*a*b*), and (0.30.5) water holding capacity, drip loss, and Warner Bratzler shear force. Muscle energy only affected muscle contraction of the A-age-pasture system (shortest sarcomere length of 1.66 μm vs 1.75 μm and highest WBS of 6 kg vs 5 kg; 7 days post-mortem).The Agricultural Research Council (ARC) is acknowledged for their facilities and THRIP and the RMRDT for financial support.www. elsevier.com/locate/meatscihb201

Effect of dietary beta-agonist treatment, vitamin D-3 supplementation and electrical stimulation of carcasses on colour and drip loss of steaks from feedlot steers

In this study, 20 young steers received no beta-agonist (C) and 100 animals all received zilpaterol hydrochloride (Z), with 1 group receiving Z while the other 4 groups receiving Z and vitamin D3 at the following levels (IU/animal/day) and durations before slaughter: 7 million for 3 days (3D7M) or 6 days (6D7M), 7 million for 6 days with 7 days no supplementation (6D7M7N) and 1 million for 9 days (9D1M). Left carcass sides were electrically stimulated (ES) and right sides not (NES). Samples were analysed fresh or vacuum-aged for 14 days post mortem. Parameters included drip loss and instrumental colour measurements. In general, zilpaterol showed increased drip loss, lighter meat, and reduced redness. Vitamin D3 supplementation could not consistently overcome these negative effects. All vitamin D3 treatments reduced drip loss of stimulated aged steaks.THRIP and the RMRDT.http://www.elsevier.com/locate/meatscinf201

Effects of a beta-agonist treatment, Vitamin D3 supplementation and electrical stimulation on meat quality of feedlot steers

In this study, 20 young steers received no beta-agonist (C), 100 animals all received zilpaterol hydrocholoride (Z), with 1 group only receiving Z while the other 4 groups received zilpaterol and vitamin D3 at the following levels (IU/animal/day) and durations before slaughter: 7 million for 3 days (3D7M); 7 million for 6 days (6D7M); 7 million for 6 days with 7 days nor supplementation (6D7M7N) and 1 million for 9 days (9D1M). Left carcass sides were electrically stimulated (ES) and the right side not stimulated (NES). Samples were aged for 3 or 14 days post mortem. Parameters included Warner –Bratzler shear force (WBSF), myofibril filament length, sarcomere length and calpastatin and calpain enzyme activity. Both ES and prolonged aging reduced WBSF (P<0.001). 6D7M, 6D7M7N and Z remained significantly tougher than C (P<0.001), while 3D7M and 9D1M improved WBSF under NES conditions. ES is more effective to alleviate beta-agonist induced toughness than high vitamin D3 supplements.THRIP and the RMRDT.http://www.elsevier.com/locate/meatscinf201

The beef tenderness model

In Phase1 of this study, three breed types (Simmentaler-, Brahman- and Nguni bulls; n = 60 each) were grain-fed and slaughtered at 12 months of age (A-age, fat-class 2). Feed was withdrawn for either three hours or 24 hours pre-slaughter. Within each feed withdrawal group, three electrical stimulation (ES) treatments were applied, viz. ES for 15 seconds, 120 seconds or no stimulation. In Phase 2, the effects of animal age and feeding regime were investigated using of A-age (feedlot and pasture), AB-age (feedlot and pasture) and B-age (pasture) animals. All carcasses were electrically stimulated for 15 seconds. Longer feed withdrawal increased dark-firm-dry (DFD) meat occurrence (pHu >6) in the Nguni and Simmentaler-cross. Brahman-cross longissimus (LL) tended to be more tender with paler colour and higher drip loss when 120 ES was applied. Longer feed withdrawal recorded higher Warner Bratzler shear force (WBSF) than three hour feed withdrawal. However, ES neutralized the effect of stress on tenderness. On average the AB-age feedlot animals produced the most tender LL followed by the B-age pasture and A-age feedlot which was similar to the AB-age pasture. A-age pasture animals produced the least tender LL steaks. The calpain proteolytic system played a pivotal role in determining the ultimate meat tenderness and although connective tissue becomes less soluble in older animals it did not play the determinant role in tenderness in this study. The intramuscular fat (< 3%) played an important role in the tenderness outcome of Nguni LL which marbled well at AB-age.We acknowledge Agricultural Research Council, Red Meat Research and Development South Africa, and Meat Industry Trust for facilities and financial support. This work is also based on the research supported in part by the National Research Foundation of South Africa (UID 75120).http://www.sasas.co.za/am201

Urinary catecholamine concentrations in three beef breeds at slaughter

Animal welfare has become an important determinant of meat quality with poor animal temperament leading to huge economic losses to the meat industry due to carcass bruising and condemnation. Handling and transport of live animals is a stressful experience for animals. The temperaments of cattle affect their behaviour and differ between breeds, i.e. studies have shown that Bos indicus types are more temperamental than Sanga and Bos taurus types. Catecholamines (CAT’s) are considered as indicators of stress, because higher concentrations of CAT’s in brain tissue were noted in animals that are better adapted to stressful situations. In the present study, urinary CAT’s of three beef breeds were determined immediately post mortem. Brahman cattle represented Bos indicus types, Simmentaler cattle represented Bos taurus types and Nguni cattle represented the Sanga type. Nguni steers showed higher urinary norepinephrine (NE) and epinephrine (E) concentrations than Brahman and Simmentaler steers. Simmentaler steers showed a higher concentration of urinary dopamine (DA) than Br and Ng. The results suggest that Nguni cattle are less stress sensitive compared to the other beef breeds studied. These observations may be due to the process of domestication and selection for specific genes that influence tameability and consequently resulting in a shift in circulating concentrations of urinary CAT’s.Peer-reviewed paper: Proc. 44th Congress of the South African Society for Animal Sciencehttp://www.sasas.co.zaam201

Effect of age and cut on tenderness of South African beef

The tenderness characteristics of 15 primal cuts of beef of three different age groups were assessed, and the most reliable cut to predict carcass tenderness was determined. Fifteen wholesale cuts from each age group, representing the full variation in fatness, were aged, cooked and underwent sensory evaluation, shear force resistance and proximate analysis. Collagen content and solubility was determined. Percentage fat was used as a covariant during statistical analyses. Tenderness, residue and collagen solubility of all cuts decreased significantly with animal age. Collagen solubility was the largest discriminant between the three age groups, while animal age had no significant effect on collagen content. Tenderness of primal cuts from the same carcass varied considerably, with collagen content and shear force resistance as the largest discriminants between the cuts. Cuts most representative of total carcass tenderness were M. Vastus lateralis, M. semimembranosus, M. gluteobiceps, M. semitendinosus and M. triceps brachii caput longum

Effect of age and cut on cooking loss, juiciness and flavour of South African beef

The juiciness and flavour characteristics of 15 aged primal beef cuts of electrically stimulated carcasses, from three different age groups, were assessed (n = 61). Cooking losses were determined and proximate analyses (moisture, fat, nitrogen and ash) were performed. Tender cuts were cooked by a dry heat method, and less tender cuts were cooked by moist heat methods. A trained panel (n=10) evaluated sensory quality characteristics including initial and sustained juiciness, aroma and flavour. Flavour intensity was the biggest discriminant between the three age groups and declined with an increase in age. Initial impression of juiciness decreased with increased age of the animal and cooking losses increased nonlinear with age, irrespective of the muscle. In contrast sustained juiciness increased with increased age. Cuts cooked according to a dry heat cooking method were reported juicier (both initial and sustained) than those cooked according to moist heat methods

The conversion of dopamine to epinephrine and nor-epinephrine is breed dependent

In previous reports, Nguni type cattle have shown to have a lower glycolytic potential with less glycogen measured in muscles 1 h post-mortem. With the release of catecholamines in the immediate pre-slaughter period, there is potential for depletion of muscle glycogen, because of the fact that epinephrine activates muscle adenylate cyclase and thereby stimulates glycogen breakdown. Epinephrine and nor-epinephrine are secreted as a result of any “fight or flight” situation. Tyrosine is a conditionally non-essential large neutral amino acid and the precursor of the neurotransmitters dopamine, nor-epinephrine and epinephrine. Ante-mortem stress experienced by an animal may be influenced by amino acids that provide substrates for neurotransmitter synthesis. The Nguni type cattle showed 55.8% and 55.1% greater urinary nor-epinephrine values than for the Brahman- and Simmental type cattle respectively. The Nguni type cattle showed 35.6% and 43.8% greater urinary epinephrine values than the Brahman- and Simmental type cattle respectively. The higher urinary nor-epinephrine and epinephrine levels measured in Nguni type cattle could either be explained by a greater neuronal out flux immediately prior to slaughter or a slower re-uptake

The influence of fat score and fat trimming on primal cut composition of South African lamb

The objectives of this study were to evaluate the primal cut composition of South African lamb carcasses with different fat scores, and to identify cuts suitable for fat trimming. Sixty grain fed Dorper lambs (rams and ewes) were divided into three groups and slaughtered at 30, 36 and 42 kg. Chilled carcass sides were subdivided into seven primal cuts. The cuts were dissected into meat (muscle, intermuscular and intramuscular fat), bone and subcutaneous fat (SCF) in order to determine the physical composition per cut and for the whole carcass. The % subcutaneous fat (SCF) in the loin increased the most (26 units) as the fat score increased from 1 to 5, followed by the flank, shoulder and neck. The % meat (lean) of the neck, thick rib and breast showed no significant change between fat scores 1 to 5, while % bone decreased significantly (>6% units). Meat and bone proportions decreased significantly with an increase in fat score for the loin, flank, leg and shoulder. The composition of the loin cut was most affected overall by changes in the fat score. Since different cuts accumulate SCF at different rates during fattening, trimming of SCF could reduce the boneless % SCF level of the major cuts such as the loin, leg and shoulder by 12, 6 and 9 units, respectively, when trimmed from SCF equal to a fat score 5 to a fat score 3. Further trimming to levels equal to a fat score 1, could reduce the % SCF by 18, 8 and 5 units, respectively on a boneless level. Considering differences in relative increase in intermuscular fat (IMF) and SCF in different cuts, the leg seems to be the most suitable cut for trimming in fat carcasses, since the IMF : SCF ratio is the lowest compared to the other larger cuts namely the loin and shoulder