D.L. Hopkins

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.

Lamb production from diverse genotypes 1. Lamb growth and survival and ewe performance.

Growth and survival of 3673 female and cryptorchid lambs representing the range of types (second cross, first cross and Merino) produced in the Australian lamb industry are reported. The lambs were sired by a selection of Poll Dorset (D; no. = 7), Texel (T; no. = 10), Border Leicester (BL; no. = 12) and Merino (M; no. = 12) rams and born to Border Leicester × Merino (BLM) and Merino (M) dams, which resulted in six lamb genotypes (D×BLM, T×BLM, D×M, T×M, BL×M and M×M). The second cross lambs (D×BLM, T×BLM) were heavier at birth, weaning and post-weaning and had higher growth rates, than first cross lambs (D×M, T×M, BL×M), which were higher than M×M lambs ( P Lamb survival to weaning was 76% and it was affected by birth weight and birth type ( P P Overall the proportion of ewes lambing was 84% with a mean litter size of 1·77. There was no difference infertility between AI (thawed frozen semen and laparoscopic insemination) and natural (single sire) mating, although the M were higher than the BLM ewes ( P P

Lamb production from diverse genotypes 2. Carcass characteristics.

Carcass and meat quality characteristics for 2408 cryptorchid and female lambs at mean carcass weights of 24·8 kg and 19·3 kg respectively are reported. The lambs were sired by a selection of Poll Dorset (D; no. = 7), Texel (T; no. = 10), Border Leicester (BL; no. =12) and Merino (M; no. =12) rams and born to Border Leicester × Merino (BLM) and Merino (M) dams. The lambs comprised six genotypes (D×BLM, T×BLM, D×M, T×M, BL×M and M×M) that represent the range of types (second cross, first cross and Merino) produced in the Australian lamb industry. The second cross (D×BLM, T×BLM) and first cross BL×M were fatter than first cross (D×M, T×M) (1 mm at the GR site) and M×M (3 mm GR) carcasses at the same hot carcass weight ( P P M. longissimus thoracis et lumborum (LL) area of first cross and second cross carcasses sired by D and T rams, which were proportionately 0·04 greater than M×M and 0·09 greater than BL×M. The LL area was proportionately 0·04 greater for T than D crosses ( P P There was a significant genotype effect for LL ultimate pH ( P

The impact of supplementing lambs with algae on growth, meat traits and oxidative status

The current study examined the effect of supplementing lambs with algae. Forty, three month old lambs were allocated to receive a control ration based on oats and lupins (n=20) or the control ration with DHA-Gold™ algae (~2% of the ration, n=20). These lambs came from dams previously fed a ration based on either silage (high in omega-3) or oats and cottonseed meal (OCSM: high in omega-6) at joining (dam nutrition, DN). Lamb performance, carcase weight and GR fat content were not affected by treatment diet (control vs algae) or DN (silage vs OSCM). Health claimable omega-3 fatty acids (EPA+DHA) were significantly greater in the LL of lambs fed algae (125±6mg/100g meat) compared to those not fed algae (43±6mg/100g meat) and this effect was mediated by DN. Supplementing with algae high in DHA provides a means of improving an aspect of the health status of lamb meat.

Case studies demonstrating the benefits on pH and temperature decline of optimising medium-voltage electrical stimulation of lamb carcasses

The efficacies of electrical stimulation practices at Australian abattoirs that process significant proportions of Australianlambandsheepmeatwereassessed.Severalabattoirsusedmedium-voltageelectricalstimulationsystem(MVS) units suboptimally and many carcasses at these abattoirs exhibited a poor rate of pH decline and, consequently, a low proportion of carcasses attained pH 6 at a carcass temperature of 1835C, according to Sheep Meat Eating Quality pH-temperatureguidelinesasadoptedbyMeatStandardsAustralia.Inthepresentcommunication,wedescribethecausesof suboptimal results withelectrical stimulation and discussprocedures for optimising thestimulation dose delivered by MVS units.CarcasspHresponsestovariouslevelsofcurrentandpulsewidthwereassessedtodeterminethebestMVSsettingsfor individual abattoirs. The MVS units at the abattoirs involved in the present study have now been programmed for optimal efficacy and carcass quality will be monitored on an ongoing basis. Evaluation of methods for assessing the proportion of carcassesthatfallwithintheoptimumpH-temperaturewindowshowedthatarandomregressionmodelismoreaccuratethan the current approach.

A national audit of retail lamb loin quality in Australia.

A retail audit of lamb loin tenderness was conducted over a 12-month period to determine the variation in tenderness of Australian lamb. Tenderness was objectively measured using Warner-Bratzler (WB) shear force. Muscle pH and cooking loss were determined on all samples and colour was measured on a sub-sample of loins. A total of 909 midloins from retail butcher shops and supermarkets located in four Australian capital cities (Sydney, Canberra, Melbourne, and Perth) were evaluated at four sampling times (December 1997 and March, June, and October 1998). Overall, 20.3% of all midloins purchased had a WB shear force value above the threshold level of 5 kg. Generic samples from Melbourne butcher shops were similar for WB shear force on average to the generic samples from Canberra and Sydney, whereas those from Melbourne supermarkets had significantly (P<0.001) higher WB shear force and were in line with generic samples from Perth. In both Canberra and Perth, alliance (branded) lamb had a greater WB shear force (P<0.05) than generic lamb. No relationship was found between price per kg and shear force (r=0.02) for loins purchased in Sydney (n=220). Price per kg differed between months (P<0.001) and suburbs (P<0.001), but not between retail butcher shops and supermarkets. Of the midloins tested, 10.3% had a pH above the critical point of 5.8. Midloins from the December 1997 sampling had a lower pH (P<0.01) than those sampled at other months. Those sampled in Melbourne and Perth had a similar mean pH, which were lower (P<0.001) than Canberra and Sydney samples. The findings from this quality audit suggest that there is room to improve the tenderness of Australian lamb sold in the domestic market. A lamb eating quality assurance system, based on set protocols, is one approach that is currently being investigated in Australia to ensure the supply of consistently high eating quality lamb to consumers.

Explaining the variation in the shear force of lamb meat using sarcomere length, the rate of rigor onset and pH

The temperature when the pH=6.0 (temp@pH6) impacts on the tenderness and eating quality of sheep meat. Due to the expense, sarcomere length is not routinely measured as a variable to explain variation in shear force, but whether measures such as temp@pH6 are as useful a parameter needs to be established. Measures of rigor onset in 261 carcases, including the temp@pH6, were evaluated in this study for their ability to explain some of the variation in shear force. The results show that for 1 day aged product combinations of the temp@pH6, the pH at 18 °C and the pH at 24 h provided a larger reduction (almost double) in total shear force variation than sarcomere length alone, with pH at 24 h being the single best measure. For 5 day aged product, pH at 18 °C was the single best measure. Inclusion of sarcomere length did represent some improvement, but the marginal increase would not be cost effective.

The effect of pH decline rate on the meat and eating quality of beef carcasses

An experiment was undertaken to examine the effect of rapid pH fall at a high muscle temperature on meat and eating quality of two beef cuts (striploin and cube roll). From 115 beef steer carcasses of which the right side of each carcass was subjected to electrical stimulation, 25 carcasses which exhibited the largest difference in the rate of pH fall in the M. longissimus between sides were selected for subsequent sampling. All of the stimulated sides missed the ‘ideal’ pH/temperature window (defined as temperature at pH 6 in the M. longissimus 12°C) at the upper end, as did several of the non-stimulated sides. The mean temperature at pH 6 for stimulated sides from modelling was 40.9 versus 33.3°C for non-stimulated sides. Despite the significant effect of stimulation on pH decline there was no statistically significant impact on shear force or sensory traits of the M. longissimus, but there was a significant effect of aging on these traits. There was no effect of stimulation or pH decline on drip loss of the striploin. After 14 days of aging there was no effect of stimulation or ultimate pH on striploin purge, but there was a significant effect of pH decline. This was not, however, evident for purge of the cube roll aged for either 4 or 42 days. The redness of the cube rolls as reflected by a* values declined with days of display, with the decline more rapid for samples aged for 42 days compared with those aged for 4 days. For meat aged and displayed identically, the a* values were on average significantly lower for meat from non-stimulated carcasses, but apart from aging there was no effect on the wavelength ratio 630/580 nm, an indicator of the formation of metmyoglobin. There was also evidence that a rapid decline in pH increased the onset of lipid oxidation.

Comparison of two instruments (G2 Tenderometer and a Lloyd Texture analyser) for measuring the shear force of cooked meat

A comparison of the peak shear force results for a Lloyd texture analyser and a G2 Tenderometer was undertaken using both sheep and beef meat. The G2 is a new version of the Tenderometer developed originally by the Meat Industry Research Institute of New Zealand and uses an electric linear motor to compress the sample, but still retains the blunt wedge-shaped ‘tooth’. By comparison the Lloyd texture analyser can be used with a shearing head derived from the Warner–Bratzler type of head. Analysis of sheep samples (n = 148) and beef samples (n = 192) of the same size revealed that the average G2 Tenderometer shear force results were ~1.3 times those for the Lloyd when testing less tender samples. An examination of the repeatability within cook block samples for these less tender sub-samples revealed a coefficient of variation of ~12% for both the Lloyd and Tenderometer instruments. For the more tender samples, the average results for the two instruments did not differ significantly, but for less tender samples it was observed that the results for the Tenderometer were more variable than those for the Lloyd texture analyser. Data on shear force generated by the G2 are not equivalent to that generated by the Lloyd and use of the G2 requires more replicates to be tested per sample to achieve an equivalent level of precision to that of a Lloyd texture analyser. As a guide only, G2 Tenderometer values can by multiplied by 0.75–0.80 to give approximate Lloyd results if required for samples of average toughness, otherwise the following model can be used Lloyd = 2.49 Tenderometer0.72.

The effect of a kiwi fruit based solution on meat traits in beef m. semimembranosus (topside).

The effectiveness of a kiwi fruit based solution for improving the tenderness of beef m. semimembranosus and the effect on colour stability was studied. Three treatments were applied; (1) injection with the solution, (2) injection with water and (3) no injection. All samples were packaged using a SmartShape™ prototype and aged for 1 or 14 days. There was a significant effect (P<0.001) of the kiwi fruit solution on shear force, with no difference between samples injected with water and those not injected. For compression of the samples no fixed effects were significant (P>0.05). Samples not injected (control) were the darkest (lowest L* values) with no difference between samples injected with water and those injected with kiwi fruit solution. Injected samples had lower a* (redness) values than non-injected samples. In general the samples not injected had higher ratio (630/580 nm) values indicating less formation of metmyoglobin.