R. D. Warner

Muscle protein changes post mortem in relation to pork quality traits

The relationship between post-mortem traits of muscle proteins and water loss traits was investigated using 84 pork loins representing the four quality traits of PSE, RSE (reddishpink, soft, exudative), RFN (reddish-pink, firm, non-exudative) and DFD. Protein solubility measurements (sarcoplasmic, myofibrillar and total) were lower and myosin denaturation (quantified by myofibrillar ATPase activity) was higher for PSE samples compared with samples from the other quality classes. RSE samples were similar to RFN samples in protein solubility and myosin denaturation, although RSE had lower values then DFD samples for protein solubility measurements. RFN samples had lower drip, thaw, cook and total water loss than RSE samples and all water loss traits were lowest for DFD samples and highest for PSE samples. Insoluble phosphorylase was the only characteristic that differentiated among PSE, RSE and RFN samples. SDS-PAGE and Western blots indicated that in PSE and RSE samples, the myofibrillar protein titin was less degraded and nebulin was more degraded compared with RFN and DFD samples. SDS-PAGE of extracted and unextracted myofibrils showed that the reduced myofibrillar solubility of PSE samples was caused by decreased extractability of the myosin heavy chain in these samples. In conclusion, although RSE samples have unacceptably high water loss, muscle protein denaturation was minimal and did not explain the low water-holding capacity.

Have we underestimated the impact of pre-slaughter stress on meat quality in ruminants?

Stress is the inevitable consequence of the process of transferring animals from farm to slaughter. The effects of chronic stress on muscle glycogen depletion and the consequent dark cutting condition have been well documented. However, there has been little examination of the consequences of acute stress immediately pre-slaughter on ruminant meat quality. New evidence is emerging to show that non pH-mediated effects on meat quality can occur through pre-slaughter stress in cattle and sheep. This paper reviews the general aspects of pre-slaughter stress in the pre-slaughter context. It then examines the impacts of pre-slaughter stressors on ruminant carcass and meat quality and considers remedial strategies for remediating and preventing pre-slaughter stress. Further quantification of the biological costs of pre-slaughter stress and the consequences to meat quality is required.

Effects of dietary factors and other metabolic modifiers on quality and nutritional value of meat

A number of technologies that increase feed efficiency and lean tissue deposition while decreasing fat deposition have been developed in an effort to improve profitability of animal production. In general, the mode of action of these metabolic modifiers is to increase muscle deposition while often simultaneously reducing fat deposition. However, there have been some concerns that the focus on increasing production efficiency and lean meat yield has been to the detriment of meat quality. The aim of this review is to collate data on the effects of these metabolic modifiers on meat quality, and then discuss these overall effects. When data from the literature are collated and subject to meta-analyses it appears that conservative use of each of these technologies will result in a 5-10% (0.3-0.5kg) increase in shear force with a similar reduction in perception of tenderness. However, it should be borne in mind that the magnitude of these increases are similar to those observed with similar increases in carcass leanness obtained through other means (e.g. nutritional, genetic selection) and may be an inherent consequence of the production of leaner meat. To counter this, there are some other metabolic factors and dietary additives that offer some potential to improve meat quality (for example immuncastration) and it is possible that these can be used on their own or in conjunction with somatotropin, approved β-agonists, anabolic implants and CLA to maintain or improve meat quality.

Genetic and environmental effects on meat quality

In order for livestock industries to consistently produce high quality meat, there must be an understanding of the factors that cause quality to vary, as well as the contribution of genetics. A brief overview of meat tenderness is presented to understand how genotype and environment may interact to influence this trait. Essentially, meat tenderness is determined from the contribution of connective tissue, sarcomere length determined pre-rigor and rate of proteolysis during ageing, as well as contributions from intramuscular fat and post-mortem energy metabolism. The influence of mutations in myostatin, the callipyge gene, the Carwell or rib eye muscle gene as well as the calpain system on meat tenderness is presented. Specific examples of interactions between the production or processing environment and genetics are presented for both sheep and cattle. The day-to-day variation in tenderness is evident across experiments and this variation needs to be controlled in order to consistently produce tender meat.

Quality attributes of major porcine muscles : a comparison with the Longissimus lumborum

Quality attributes of the longissimus lumborum (LL) were compared to the attributes of the muscles semimembranosus (SM), rectus femoris (RF), biceps femoris (BF), gluteus medius (GM) and the lateral portion of the semitendinosus (ST) in the ham, the psoas major (PM) in the loin and the supraspinatus (SS), infraspinatus (IS) and triceps brachii (TB) in the shoulder. Carcasses were allocated to quality groups based on measurements of muscle exudate and lightness (CIE-L(∗)) in the LL. The SM, BF, GM and ST in the ham were similar to the LL (P > 0·05) in meat ultimate pH (pHu) and exudate and the GM, ST and LL were similar (P > 0·05) to the LL in lightness. The TB, RF, SS, PM and IS were similar (P > 0·05) in exudate, lightness and pHu and compared to the LL, were less exudative (P < 0·05) and darker (P < 0·05). When the LL was classed pale, and exudative, the GM, BF, SM and ST were also pale and exudative but the other muscles were darker and non-exudative. When the LL was classed dark and non-exudative, all other muscles were dark, non-exudative and the pHu was high. Therefore, the LL could serve as a reliable indicator of colour and exudate for all porcine musculature when the condition was dark and non-exudative (i.e. DFD). However, when the condition was pale and exudative (i.e. PSE), then the LL would serve as a reliable indicator only for the four major ham muscles, excluding the RF.

A structural approach to understanding the interactions between colour, water-holding capacity and tenderness.

The colour, water-holding capacity (WHC) and tenderness of meat are primary determinants of visual and sensory appeal. Although there are many factors which influence these quality traits, the end-results of their influence is often through key changes to the structure of muscle proteins and their spatial arrangement. Water acts as a plasticiser of muscle proteins and water is lost from the myofibrillar lattice structure as a result of protein denaturation and consequent reductions in the muscle fibre volume with increasing cooking temperature. Changes in the myofilament lattice arrangement also impact the light scattering properties and the perceived paleness of the meat. Causes of variation in the quality traits of raw meat do not generally correspond to variations in cooked meat and the differences observed between the raw muscle and cooked or further processed meat are discussed. The review will also identify the gaps in our knowledge and where further investigation would beneficial.

Comparison of CO2 stunning with manual electrical stunning (50 Hz) of pigs on carcass and meat quality

The effects of carbon dioxide stunning on carcass and pork quality attributes were compared with the effects of manual electrical stunning using either head-only or head-to-brisket electrodes. A total of 30 Large White×Landrace boars (homozygous dominant for the halothane gene) were randomly allocated immediately prior to slaughter to one of three stunning treatments: carbon dioxide (90% CO2), head only (HO; 1.3 A for 4 s at a frequency of 50 Hz) or head to brisket (HBR; 1.3 A for 4 s at a frequency of 50 Hz) electrical stunning. The pH of the M. longissimus thoracis (LT) muscle measured at two sites [between the fifth and sixth thoracic vertebrae (Site 1) and the last thoracic rib (Site 2)] at 40 min post-slaughter was lower (P 0.05) between stunning methods was found in the LT muscle at Site 2. Pork from HBR stunned pigs was paler (P<0.05) and had a higher (P<0.001) percentage drip loss compared with pork from HO and CO2 stunned pigs. LT muscles from HBR stunned pigs had lower (P<0.001) WB shear force values compared with pork from HO stunned pigs (6.57 vs. 8.12 kg, S.E.D. 0.49). Carcass quality was improved by CO2 stunning, with less (P<0.05) ecchymosis-affected pork trimmed from shoulder primals compared with electrically stunned pigs. These results indicate that manual electrical stunning of pigs using HO tongs and CO2 stunning reduced percentage drip loss, reduced muscle lightness and reduced the rate of muscle pH decline compared with pigs manually electrically stunned using HBR tongs.

The effect of handling pre-slaughter and carcass processing rate post-slaughter on pork quality

Forty-eight male crossbred (Large White-Landrace) pigs were used in a 2×2 factorial design to determine the effect of pre-slaughter handling (minimal and negative handling prior to slaughter) and the rate of carcass processing post-slaughter [normal rate (45min) and delayed rate (70min) from time of exsanguination to carcass entering the chiller] on muscle glycolysis and pork quality. Pigs negatively (using an electric goad) handled at the abattoir just prior to slaughter had lower muscle glycogen concentrations in the Longissimus thoracis (LT) and the Biceps femoris (BF) at all times post-slaughter and lower lactic acid at 5, 45 and 70min post-slaughter compared to pigs minimally (no use of electric goads) handled prior to slaughter. Negative handling of pigs just prior to slaughter also resulted in pork which had higher surface exudate and a higher incidence of PSE compared with pigs minimally handled prior to slaughter. A prolonged rate of carcass processing resulted in reduced muscle glycogen in the LT and BF at all times post-slaughter. Delays in carcass processing rate also affected pork quality, as the meat was paler in comparison with pig carcasses that were processed without any delays. The results from this experiment have indicated that the use of electric goads to move pigs at the abattoir, and delays in carcass processing post-slaughter, can have a detrimental influence on ultimate pork quality.

Genetic parameters for meat quality traits of Australian lamb meat

Genetic parameters were estimated for a range of meat quality traits recorded on Australian lamb meat. Data were collected from Merino and crossbred progeny of Merino, terminal and maternal meat breed sires of the Information Nucleus programme. Lambs born between 2007 and 2010 (n=8968) were slaughtered, these being the progeny of 372 sires and 5309 dams. Meat quality traits were found generally to be of moderate heritability (estimates between 0.15 and 0.30 for measures of meat tenderness, meat colour, polyunsaturated fat content, mineral content and muscle oxidative capacity), with notable exceptions of intramuscular fat (0.48), ultimate pH (0.08) and fresh meat colour a* (0.08) and b* (0.10) values. Genetic correlations between hot carcass weight and the meat quality traits were low. The genetic correlation between intramuscular fat and shear force was high (-0.62). Several measures of meat quality (fresh meat redness, retail meat redness, retail oxy/met value and iron content) appear to have potential for inclusion in meat sheep breeding objectives.

Comparison of different dietary magnesium supplements on pork quality

Forty-eight crossbred (Large White×Landrace) boars were used to compare the effect of dietary magnesium aspartate (MgAsp), magnesium sulphate (MgSO(4)) and magnesium chloride (MgCl(2)) on muscle glycogenolysis and pork quality. The pigs were fed finisher feed supplemented with either MgAsp, MgSO(4) and MgCl(2) for 5 days prior to slaughter. At the abattoir, all pigs received 15 electric shocks from an electric goad 5min prior to slaughter. Pigs fed the diet supplemented with MgSO(4) had the highest plasma Mg concentrations at slaughter in comparison with pigs fed the MgAsp and MgCl(2) supplemented diets. There were no differences in plasma adrenaline and noradrenaline concentrations at slaughter between the different diets. Pigs fed the Mg diets had higher muscle glycogen concentrations in the Longissimus thoracis (LT) muscle at 5min and at 40min (except MgCl(2)) post-slaughter compared to pigs fed the control diet. Also pigs fed the Mg diets had lower muscle lactic acid concentrations in the LT at 5min post-slaughter and lower drip loss at 24hr post-slaughter compared to pigs fed the control diet. These results indicate that cheaper magnesium sources, MgSO(4) and MgCl(2), are as efficacious as MgAsp in reducing drip loss and improving pork quality.