Showing papers by "John Mitchell Thompson published in 2005"

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

Abstract: 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)

Effects of animal age on the eating quality of sheep meat

Abstract: The aim of this work was to test the effects of animal age on consumer perceptions of sheep meat quality. Experiment 1 tested eating quality scores (tenderness, liking of flavour, juiciness and overall liking) derived from untrained consumers of grilled M. longissimus lumborum (LL) or M. biceps femoris (BF) derived from Merino ewes ranging from 8.5 to 68.5 months of age. The ewes were derived from one farm and all received a pelleted diet (60% hay, 30% lupin grain and 10% barley grain) that sustained growth between 118 and 173 g/day for at least 22 days pre-slaughter. In experiment 2 consumer testing of grilled LL and roasted BF and M. semimembranosis (SM) was conducted on a commercial line of 12-month-old White Suffolk × Merino lambs (0 erupted incisor teeth) v. a line of Merino yearling sheep about 22 months old (with either 2 or 4 erupted incisor teeth). The results of experiment 1 showed a significant effect of muscle (LL>BF, P<0.001) and a cubic effect of animal age on the consumer scores for grilled steaks. The cubic relationship was due to meat from lamb (8.5 months) and hogget (20 months) having higher scores than those of older animals. There was a close relationship between the objective measures of tenderness and the consumer tenderness score (r2 = 0.53, P<0.001). Results of experiment 2 indicated no significant difference between the grilled LL for the crossbred lamb and 22-month-old (2–4 teeth) Merino yearling sheep. However, the consumer scores for the roasted BF and SM were significantly depressed in the 2–4 tooth yearling Merino categories. In conclusion, this work clearly underpins the current Australian definition of lamb, lamb having better eating-quality attributes than older animals with fully erupted permanent incisor teeth, particularly in muscles from across the carcass. However, this work also highlights the eating quality attributes of older sheep (6 or more permanent incisor teeth) particularly for the LL, and suggests that negative influences of flavour associated with older sheep meat are minimal when the product is served in the absence of subcutaneous and intermuscular fat. Finally, the results suggest the possibility of a new ‘yearling’ sheep meat category based on animals in the 2–4-tooth dentition category.

Development of a sensory protocol for testing palatability of sheep meats

Abstract: A total of 108 grill and 108 roast samples were prepared from lamb (n = 10) and mutton (n = 8) carcasses for sensory testing using a consumer taste panel. Grill and roast samples were prepared from the left and right sides of the carcass, respectively, using longissimus, biceps femoris, gluteus medius, serratus ventralis and semimembranosus. Due to size constraints, muscle from both sides was used to form grill samples for the vastus lateralis, and roast samples from the triceps brachii. Grill and roast samples were sensory tested using 360 untrained consumers. Each consumer was given a total of 6 experimental samples and each sample was tested by 10 different consumers. Sensory scores for tenderness, juiciness, like flavour and overall liking from both the grilled and roasted samples were highly correlated (P 0.05). In contrast, juiciness and like flavour scores were poorly correlated between grilled muscles. For the roasted samples, sensory scores were generally uncorrelated between muscles. The statistical significance of the age category and muscle effects was greater in grill samples, but stimulation effects were of similar significance using either cooking method. It was proposed that roasting reduced treatment effects that affected sensory via differences in connective tissue toughness, due to gelatinisation of connective tissue during cooking. For testing production and processing effects on palatability, grilling was more sensitive for detecting treatment effects, than roasting.

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

Abstract: 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.

Effect of sheep type on meat and eating quality of sheep meat

Abstract: The effect of type of lambs and hoggets on eating quality was evaluated using the M. longissimus lumborum (LL) and the M. biceps femoris (BF) from 210 animals. The animals comprised 7 types as follows: Poll Dorset or White Suffolk x (Border Leicester x Merino) (second cross unweaned lambs, mixed sex, 3-5 months of age); Poll Dorset x (Border Leicester x Merino) (second cross weaned lambs, mixed sex, 9-12 months of age); Border Leicester x Merino (BLM; first cross weaned lambs, mixed sex, 9 months of age); Poll Dorset or White Suffolk x Merino (PDM; first cross weaned lambs, wethers, 12 months of age); Merino x Merino (weaned wether lambs, 9-12 months of age); Border Leicester x Merino (BLM; first cross hoggets, mixed sex, 20 months of age); and Poll Dorset or White Suffolk x Merino (PDM; first cross hoggets, wethers, 16 months of age). The animals were sourced from a number of different properties in New South Wales (NSW) (n = 120) and Victoria (n = 90). Each carcass was subjected to high voltage stimulation (700 V) within 1 h of slaughter. All meat was aged for 5 days before freezing and was subsequently tested by consumers on a 0-100 scale for a number of attributes after cooking using a grilling procedure. The LL from sucker lambs had the lightest colour (highest L* values) with the hoggets having the darkest colour in the NSW group with differences less apparent in the Victorian group. Muscle from first cross and Merino weaned lambs had consistently higher pH levels across the 3 muscles tested (LL; M. semimembranosus; M. semitendinosus) for the NSW group with no differences detected in the Victorian group. LL meat from second cross sucker and first cross (BLM and PDM) weaned lambs had the highest overall liking score, with that from second cross weaned lambs, BLM hoggets and Merino lambs scored as intermediate, while meat from the PDM hogget group had the lowest overall liking score. A similar outcome was found for the other sensory attributes with differences between types being lower for juiciness compared with overall liking scores but they were of a similar ranking. For the BF there was some re-ranking of the overall liking scores compared with the LL, with meat from suckers and first cross PDM lambs and hoggets being intermediate in score while second cross weaned lambs and first cross BLM lambs had the highest scores. The BF from hoggets (BLM) and Merino lambs were given the lowest scores. The lower juiciness score for sucker BF contributed to this change in ranking compared with the LL.

New electrical stimulation technologies for sheep carcasses

Abstract: High voltage electrical stimulation applied to the lamb carcass at the end of the dressing procedure often leads to an improvement in overall product quality by reducing the incidence of toughness. It would be advantageous if the same results could be consistently achieved with the use of lower, safer, voltages - medium voltage electrical stimulation. Experiments were conducted to determine the effect of medium voltage electrical stimulation applied to wool-on carcasses on meat quality as assessed using the Sheep Meat Eating Quality protocols. A further experiment examined the interaction of electrical stimulation and meat aging time on the consumer acceptance of lamb meat. In the first experiment, 3 treatments: control (non-stimulated), medium voltage electrical stimulation (applied to the wool-on carcass) and high voltage electrical stimulation (applied at the completion of dressing) were examined. Samples of the loin (LTL) and rump (GM) muscles were evaluated by consumers using Sheep Meat Eating Quality protocols. For both muscles, the consumers gave higher scores for tenderness, juiciness, flavour and overall acceptability to the stimulated product (P<0.001). There were no statistically significant differences between the 2 stimulation treatments. The second experiment was conducted at a commercial lamb-processing abattoir that had installed a prototype automated electrode system designed to work at chain speed. Lambs received either no stimulation (control), low current medium voltage electrical stimulation (constant current 300 mA peak, 15 Hz, maximum voltage 550 V peak) or high current medium voltage electrical stimulation (constant current 600 mA peak, 15 Hz, maximum voltage 550 V peak) immediately after sticking. Electrical stimulation improved both the objective and sensory (Sheep Meat Eating Quality) eating quality attributes of lamb loin muscle when assessed following 2 days of ageing. When expressed according to consumer satisfaction rating, 30, 37 and 70% of the loins receiving low, high or no electrical stimulation, respectively, were rated as unsatisfactory at 2 days of ageing. At 4 days of ageing no loins from carcasses in the low stimulation treatment were rated by consumers to be unsatisfactory (P<0.05) compared with either non-stimulated (40%) or high-stimulated loins (35%). With respect to the effects of aging meat, electrical stimulation improved the consumer score at 2 days post-stunning by 8.9 and 4.7 points for tenderness and overall liking, respectively. Further linear improvements due to aging were similar for both electrical stimulation and unstimulated products. Under conditions of no electrical stimulation used in this experiment, 10 days aging results in tenderness and overall liking scores greater than 60 and with ES similar scores are achieved in 5 days. Consumer scores over 60 greatly reduce the chance of meat being classified as unsatisfactory.

Muscle metabolism in relation to genotypic and environmental influences on consumer defined quality of red meat

Abstract: This paper discusses the management of consumer defined beef palatability using a carcass grading scheme which utilizes the concept of total quality management. The scheme called Meat Standards Australia (MSA) has identified the Critical Control Points (CCPs) from the production, pre-slaughter, processing and value adding sectors of the beef supply chain and quantified their relative importance using large-scale consumer testing. These CCPs have been used to manage beef palatability in two ways. Firstly, CCPs from the pie-slaughter and processing sectors have been used as mandatory criteria for carcasses to be graded. Secondly, other CCPs from the production and processing sectors have been incorporated into a model to predict palatability for individual muscles. The CCPs from the production (breed, ossification and implants of hormonal growth promotants), pre-slaughter and processing (pH/temperature window, alterative carcass suspension, marbling and ageing) sectors are reviewed. The paper then discusses the interacting roles of nutrition and genotype as determinants of muscle energy pattern with respect to glycogen and fat metabolism. In particular the roles of fibre type and/or pattern of muscle energy metabolism is discussed in relation to the high ultimate p11 syndrome (dark cutting beef), the rate of post mortem glycolysis and the response to electrical stimulation. Finally the development of intramuscular fat is discussed in terms of growth and development, biochemical regulation and nutritional modification.

A model relating a function of tenderness, juiciness, flavour and overall liking to the eating quality of sheep meat

Abstract: A probabilistic model of consumer perception of sheep meat eating quality is constructed on the basis of a sensory score derived from consumer evaluation of tenderness, juiciness, flavour and overall liking. The model includes consideration of the variability of the sensory score within a mob, the probability that meat with a given sensory score will be perceived by the consumer as correctly classified, and the distribution of the average sensory score within an eating quality grade. Based on this information the model can calculate the frequency with which sheep meat given a sensory score that will fail to meet the consumer expectation of the allocated eating quality grade. The model provides a basis for integrating the information gathered on sheep meat eating quality to formulate a method of classification and to quantify the reliability of this classification. This information can be applied in a variety of ways to evaluate the efficacy, financial or otherwise, of a retailer adopting a given sheep meat eating quality classification based on the nominated eating quality score.

The effect of lairage time on consumer sensory scores of the M. longissimus thoracis et lumborum from lambs and lactating ewes

Abstract: The aim of this study was to determine whether lairage time influenced consumer sensory scores of the eating quality of lamb and mutton. Commercial consignments of lambs and ewes were subjected to 3 different lairage periods (slaughter on arrival, slaughter after 1 day or slaughter after 2 days in lairage) at one site in Victoria (experiment 1) and another site in Western Australia (experiment 2). In experiment 1, 3 sucker and 3 carry-over lamb consignments, each consisting of 36 lambs, were sourced from a public saleyard. In experiment 2, 3 ewe and 3 lamb consignments, each consisting of 150 animals were sourced directly from the farm of origin. There was no primary effect of lairage time on consumer sensory scores of the M. longissimus et lumborum from either lambs or ewes at the 2 locations. Sucker lambs were tenderer than carry-over lambs in experiment 1. There was an interaction between age class and lairage time for tenderness in experiment 2, such that lamb meat was tenderer than ewe meat when slaughtered after 1 day in lairage. Ewes produced loins with shorter (0.6 μm, P<0.05) sarcomere length, higher (4.9%, P<0.05) intramuscular fat percentage and darker (P<0.05) meat colour compared with those from sucker lambs. Hue angle was higher (2°, P<0.01) for meat from sheep killed after 1 day in lairage compared with meat from sheep killed on arrival or after 2 days in lairage in both experiments.

The effect of design and demographic factors on consumer sensory scores

Abstract: The importance of design and demographic effects on sensory scores for tenderness, juiciness, like flavour and overall liking scores was examined using a dataset of 24 840 untrained consumer tastings on 2484 grilled sheep meat samples, from 4140 consumers. These samples were tasted as part of 23 separate taste panels, each made up of 9 separate sessions each comprising of 20 different consumers. Before undertaking the tastings, each consumer provided demographic details detailing age class, gender, occupation, frequency of eating meat, number of adults and children living in the household, their appreciation of meat, preferred degree of doneness and income category. Taste panel had a significant (P 0.05). All 4 sensory scores were affected (P 0.05) for any of the 4 sensory scores. It was concluded that demographic effects had only a minor impact on sensory scores. This inferred that the need to balance consumer demographics for sensory panels was relatively unimportant.

Extending the Bayesian Mixture Model to Incorporate Spatial Information in Analysing Sheep CAT Scan Images

Abstract: The purpose of CAT scanning in some animal science experiments is to provide estimates of the proportion of the tissues, fat, muscle, and bone present in an individual body, and compare some of the density characteristics. In this paper we present an extension to the hierarchical Bayesian Normal mixture model, which incorporates some of the information provided by the neighbouring pixels in a CAT scan image. This neighbour information is included in the model through the use of a Markov random field for the component allocation variable. This extended mixture model provides a more responsive fit to the local likelihood of the data than that of the independent mixture model. The effectiveness of this modelling technique is illustrated by comparing its performance with that of a Normal mixture model and a fixed boundary method in 3 examples. In these examples it is shown that the extended mixture model we propose is most useful in situations that involve only slight separation of components. The advantages of the model decline as the separation of components increases.

The effect of nutrition on muscle pH decline and ultimate pH post-mortem in sheep and cattle

Abstract: Summary This paper reviews the effect of nutrition on rate of post–mortem pH decline, pH change after electrical stimulation (delta pH) and ultimate pH in skeletal muscle of sheep and cattle. The importance of muscle glycogen concentration as a determinant of ultimate pH, delta pH and rate of pH decline post–mortem is illustrated. As delta pH and rate of pH decline are increased by high muscle glycogen concentration, nutrition may affect the rate of pH decline through its effect on glycogen concentration. Muscle type also has an effect on the rate of pH decline: white muscles comprised of fast glycolytic fibres have greater rates of pH decline and delta pH than red, oxidative muscles. The effect of nutritional restriction on muscle fibre type and rate of pH decline through its effect on physiological maturity and metabolic enzyme expression is discussed.

The impact of selection for muscling on carbohydrate metabolism

Abstract: Background -- An adequate level of muscle glycogen at the time of slaughter is essential for ensuring the production of premium quality meat, and minimising the incidence of dark cutting in cattle and sheep. Muscle glycogen status is likely to reflect the rate of turnover, principally driven by the sensitivity of muscle to insulin/nutrition, and adrenalin/stress. Breed indices for sheep and cattle are focused towards selection for muscling, potentially impacting on muscle glycogen metabolism and thus dark cutting. Objective -- Determine the impact of selection for muscling on insulin and adrenalin sensitivity in cattle and sheep. Design -- 12 steers from either Piedmontese (heavy muscling genotype), or Angus sires, and 20 5-month old lambs with sires selected for extremes (high v low) in Muscling Estimated Breeding Value (EBV) were maintained on a pelleted concentrate ration and challenged with adrenalin at 0.1, 0.2, 0.4, 0.6, 0.9, 1.2, and 1.6 µg/kg liveweight via indwelling jugular cathetars. In cattle these challenges were undertaken at 15 and 36 months. Blood samples were taken prior to, and up to 120 min following administration of challenges for the determination of plasma lactate concentration -- an indicator of muscle response. Peak plasma lactate response was analysed for either difference between breeds (Angus or Piedmontese) or impact of Muscling EBV (sheep analysis) using a linear mixed effects model, with level of adrenalin challenge and basal lactate concentration as covariates, and animal as a random term. Outcomes -- Increasing adrenalin challenge lead to a linear (lambs) and curvilinear (cattle) increase in plasma lactate peak response (P <0.05; Fig. 1a & b). The slope of this increase for the low muscle EBV lambs (ie EBV = -2) was more than twice (P <0.05) that of the high, suggesting that high muscle EBV lambs are less sensitive to adrenaline at the level of the muscle. In cattle there was no difference between breeds at 15 months, but both breeds demonstrated increased adrenalin sensitivity at 36 months (P <0.05). In the Angus sired cattle, the increase in sensitivity (ie slope) was almost twice that of the more heavily muscled Piedmontese (P <0.05). Thus, as was the case in lambs, the more heavily muscled genotypes are less sensitive to adrenaline at the level of the muscle. Conclusions -- Selection for muscling will reduce stress sensitivity in muscle tissue potentially resulting in more muscle glycogen at slaughter, and less dark cutting in sheep and cattle.