D.N. D'Souza

The impact of processing on sensory and objective measurements of sheep meat eating quality

The impact of processing factors on sheep meat eating quality was investigated in an experiment in which stimulation (stimulation and no stimulation), chilling rate (fast and slow chilling) and carcass suspension (tenderstretch and normally hung by Achilles tendon) treatments were overlaid on 80 lamb and 40 mutton carcasses processed over 2 days, at 2 different abattoirs. Within each carcass, 3 muscles (M. longissimus thoracics et lumborum, biceps femoris and serratus ventralis) were collected from both sides and aged for 2 of 3 ageing periods (2, 5 or 14 days), before sensory testing for tenderness, juiciness, like flavour and overall liking, using a consumer taste panel. Processing treatments of stimulation and chilling were variable in their effect on the rates of pH and temperature decline and temperature at pH 6 (temp@pH6), between the 4 slaughter groups. Therefore chilling rate and electrical stimulation were considered as tools by which temp@pH6 could be manipulated, rather than as treatment effects per se. Age category (lamb or mutton) had the largest impact on tenderness score, followed by muscle, ageing and carcass suspension. There were significant interactions for tenderness and overall liking scores between muscle × ageing, age category × muscle and carcass suspension × muscle (P 30°C) or low (<10°C) temp@pH6. There was a tendency for sensory scores (particularly for the like flavour score) to decline for the biceps femoris when it was stored for extended periods (14 days).

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.

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.

Nutritional manipulation increases intramuscular fat levels in the Longissimus muscle of female finisher pigs

Fifty crossbred (Large White x Landrace x Duroc) female finisher pigs were used to determine the effect of nutritional manipulations on intramuscular fat deposition. The main nutritional treatments were (i) Control (pigs fed a commercial grower diet), (ii) -15% P:DE (pigs fed a 15% reduced protein:digestible energy diet during the grower phase), (iii) -30% P:DE (pigs fed a 30% reduced P:DE diet during the grower phase), (iv) +6% Fat (pigs fed diet supplemented with 6% additional fat during the grower phase), and (v) -Vit A (pigs fed a control diet with no supplemented Vit A in the mineral vitamin premix during the grower and finisher phase). Pigs fed the 30% reduced P:DE diet had an inferior feed to liveweight gain (feed conversion ratio, FCR) for the combined grower and finisher growth period (P = 0.036) compared with the other dietary treatments. There were no significant differences in average daily gain (ADG) or voluntary feed intake (VFI) for the grower, finisher, and the combined grower and finisher phases, or liveweight at slaughter between the dietary treatments. Pigs fed the 15% (1.9%) and 30% (2.7%) reduced P:DE diet, and the Vit A-restricted diet (2.0%), had significantly higher intramuscular fat (IMF) levels compared with pigs fed the other diets. Pigs fed the control diet had higher (P = 0.002) carcass dressing percentage compared with pigs fed the other diets. There were no significant dietary effects on total fat tissue (P = 0.661), total lean muscle tissue (P = 0.637), and total bone mineral (P = 0.367) content. In conclusion, these data indicate that feeding pigs grower diets with 15% and 30% reduced P:DE, and grower and finisher diets restricted in Vit A, improved the IMF levels in the Longissimus muscle. The increase in IMF levels in pigs fed the 15% reduced P:DE diet, and grower and finisher diets restricted in Vit A, improved the IMF levels without having a detrimental effect on growth performance and carcass quality.

The effect of dietary treatment on meat quality and on consumer perception of sheep meat eating quality

The aim of this experiment was to test the effects of dietary treatment on sheep meat eating quality as perceived by untrained Australian consumers. Six-month-old Suffolk x Merino lambs (n = 192) were allocated to 1 of 4 nutritional treatments for 60-77 days and were fed: (i) an irrigated perennial ryegrass-clover-kikuyu sward; (ii) irrigated perennial ryegrass-clover-kikuyu pasture for 48-61 days then poor quality straw for the last 12-16 days; (iii) a mixed ration treatment consisting of a high-energy pelleted diet (40% barley grain, 30% wheat grain, 15% hay and 12% lupin grain); or (iv) irrigated pasture for 37-51 days followed by a moderate-energy pelleted diet (36% wheat grain, 35% hay and 24.5% lupin grain) for 23-26 days. The starting liveweight of lambs was 31.5-35.5 kg and the final hot carcass weight was 19-20 kg. The nutritional treatment finishing system employing straw feeding for the last 12-16 days was associated with a loss of liveweight during this period, a decreased tissue depth at the GR site and a decreased content of intramuscular fat and glycogen in muscle. Untrained Australian consumers were asked to rate samples (scale 0-100) of the M. longissimus thoracis et lumborum (LL) from lambs for tenderness, liking of flavour, juiciness and overall liking and then classify the meat as unsatisfactory, good everyday or better than everyday. Straw feeding was also associated with significantly reduced consumer scores for juiciness (P<0.05) and liking of flavour (P<0.10) with no changes in tenderness and overall liking. There was no significant difference in the consumer acceptance of the LL obtained from lambs finished on pasture v. grain-based diets. It is concluded that nutritional finishing systems should be selected to prevent animals from losing weight pre-slaughter and that decisions on pasture v. grain based feeding systems be based on the cost of production.

The accuracy of dual energy X-ray absorptiometry (DXA), weight, and P2 back fat to predict half-carcass and primal-cut composition in pigs within and across research experiments

A Hologic QDR4500A dual energy X-ray absorptiometer (DXA) was used to measure body composition in 199 half-carcasses ranging from 15 to 48 kg. Half-carcasses were from animals of mixed sex and of either Large White × Landrace or Large White × Landrace × Duroc descent. Half-carcasses were selected from 5 different experiments to evaluate DXA accuracy within and across experiments. Values determined by DXA including total tissue mass, fat tissue mass, lean tissue mass, and bone mineral content, for the half-carcass and the shoulder, loin, belly, and ham primal cuts were evaluated by comparison with manually dissected composition. Relationships between manually dissected values and measurements of weight and backfat at the P2 site were also evaluated. Manually dissected values were strongly related to DXA-derived values, more so than with weight and P2 or a combination of both, particularly in the measurement of fat composition. In contrast to estimates derived from weight and P2, DXA-derived estimates remained accurate even when between-experiment variation was included. However, because DXA estimates were different from manually dissected values, they would need to be adjusted with the use of appropriate regression equations to correct the in-built algorithms. These results demonstrate the efficacy of DXA as a non-destructive method for determining the composition of the half-carcass and primal cuts, and its greater precision than current routinely used methods. Additional keywords: dissection, lean tissue, fat, belly, REML.

Ractopamine supplementation increases lean deposition in entire and immunocastrated male pigs

Sixty entire male pigs (Large White × Landrace × Duroc crossbred) were individually reared from 45 to 114 kg liveweight in a 2 by 3 factorial experiment to determine the interactive effects of sex (entire male pigs v. male pigs immunologically castrated using Improvac with vaccinations administered at 13 weeks of age and 5 weeks before slaughter) and a ractopamine feeding program (constantly fed 0 or 5 ppm ractopamine for 26 days before slaughter v. a step-up program where 5 ppm of ractopamine was fed for 14 days followed by 10 ppm ractopamine for the final 12 days before slaughter) on growth performance, carcass composition and pork quality. Following the second vaccination, immunocastrated pigs ate more (P 0.05) in both entire and immunocastrated male pigs. The effects of dietary ractopamine and immunocastration were additive, such that pigs that were immunocastrated and received ractopamine grew 18% faster than control entire males. However, a step-up program of ractopamine supplementation did not provide further improvements in growth performance and carcass composition when compared with constant 5 ppm ractopamine supplementation. These findings indicate that ractopamine supplementation improved growth performance in entire and immunocastrated male pigs, thereby offering a means of improving growth performance of entire males without detrimental effects on pork quality.

The influence of dietary magnesium supplement type, and supplementation dose and duration, on pork quality and the incidence of PSE pork

Ninety crossbred (Large White × Landrace) female pigs were used to compare the effects on ultimate pork quality of different magnesium (Mg) compounds [magnesium aspartate (MgAsp) and magnesium sulfate (MgSO4)], Mg dose (1.6 and 3.2 g elemental Mg), and Mg supplementation period (2 and 5 days) in pigs subjected to an acute stressor pre-slaughter. Pigs fed the Mg-supplemented diets had lower muscle lactic acid concentrations at 24 h post-slaughter than pigs fed the control diet. There were no significant differences in muscle glycogen concentrations in the Longissimus thoracis (LT) at 5 min, 40 min, or 24 h post-slaughter between the control and Mg-supplemented diets. Pigs fed the Mg-supplemented diets produced less pale colour pork (i.e. darker colour) and had reduced drip loss and reduced incidence of pale, soft, exudative (PSE) pork in the LT muscle compared with pigs fed the control diet. Within the Mg diets, pigs fed the MgAsp-supplemented diet produced less pale LT muscle colour than pigs fed the MgSO4-supplemented diet. There were no significant differences in LT pork quality parameters (colour and percent drip loss) regardless of whether the high or low Mg dose or the 2- or 5-day supplementation period was used. This experiment has shown that the use of dietary MgAsp supplementation at a dose of 1.6 g elemental Mg (20 g MgAsp) for 2 days prior to slaughter significantly improved pork quality and reduced the incidence of PSE pork.

Quantifying the hydration status of lambs in relation to carcass characteristics

An experiment was undertaken to determine the physiological effects of water deprivation on lambs before slaughter. The aim of this experiment was to develop a method for quantifying the hydration status of lambs in relation to any subsequent effects on carcass and meat characters. Forty-eight crossbred lambs were subjected to 1 of 4 treatments: (i) normal ambient air temperature with access to water; (ii) normal ambient with no access to water; (iii) high ambient air temperature with access to water; and (iv) high ambient air temperature with no access to water. The treatments were imposed for a period of 48 h, after which the lambs were slaughtered. Food was withheld from all lambs during this 48 h period. Serum and urine were collected from each lamb at 0, 24 and 48 h and the concentrations of a range of analytes measured. Muscle, viscera and gastrointestinal tract were sampled immediately after slaughter. Water deprivation for a period of 48 h caused an increase in liveweight loss but no change in hot carcass weight or dressing percentage. Water deprivation caused an increase in muscle dry matter concentration and osmolality. The concentrations of protein, ;2-hydroxybutyrate, glucose, creatinine, potassium or albumin in serum were not affected by water deprivation. The concentration of sodium and chloride ions in serum and urine increased with feed deprivation time in lambs which had no access to water, but did not change for lambs that had access to water. Interactions occurred between water access and ambient air temperature for some but not all parameters. A significant relationship was found between muscle dry matter concentration, serum sodium concentration and urine specific gravity. It was concluded that urine specific gravity is a sensitive indicator of water consumption. Serum sodium concentration and urine specific gravity used together may be useful to predict the muscle hydration status of lambs.

Aitchbone hanging and ageing period are additive factors influencing pork eating quality

The effects of abattoir, carcase weight (60 or 80 kg HCW), hanging method (Achilles or aitchbone) and ageing period (2 or 7 day post-slaughter) on eating quality attributes of pork were investigated in this 3×2×2×2 factorial study. A total of 144 Large White×Landrace female pigs were slaughtered at one of three abattoirs and sides hung from either the Achilles tendon or the aitchbone. After 24 h chilling, loin (M. longissimus thoracis et lumborum) and topside (M. semimembranosus) muscles were individually vacuum packaged and aged for 2 or 7 days post-slaughter. Consumers (n=852) evaluated eating quality. Neither abattoir nor carcase weight influenced tenderness, flavour or overall liking of pork. Improvements in tenderness, flavour and overall liking were found due to aitchbone hanging (P<0.001) and ageing (P<0.001) for 7 days compared with Achilles-hung carcases and pork aged for 2 days, respectively. This study demonstrated that aitchbone hanging and 7 day ageing can improve eating quality, but these effects were additive as the interaction term was not significant.