Spray chilling of lamb carcasses

Two spray-chilling treatments were developed to improve appearance and reduce weight loss during lamb chilling. Rates of cooling and weight loss and meat quality were compared to conventionally chilled carcasses.

The first treatment was an intermittent spray during the first 3 h of chilling. The second consisted of only two sprays at 2 h and 10 h post mortem. The conventional control was a two-stage process, with air at 10°C and 1 m/s up to 10 h post mortem, followed by air at 0°C and 1 m/s for a further 14 h.

Both treatments significantly reduced weight loss at 24 h post mortem compared to conventional, from 2·20% to 0·86% and 1·20%, respectively. During a further 4 days storage, the savings were maintained, with weight losses being 3·97%, 2·97% and 3·19%, respectively.

There were small (<1 h) but significantly reductions in the cooling times of spray-chilled loins and legs, attributed to sustained evaporative cooling of the continually wetted surfaces.

No effects on texture or drip loss and only slight effects on surface lean and fat colour were found. Variation in texture between animals within treatments was far greater than between treatments and could not be accounted for by variations in cooling rates.     

The chilling of carcasses

Biochemical processes and structural changes that occur in muscle during the first 24h postmortem play a great role in the ultimate quality and palatability of meat and are influenced by the chilling processes that carcasses are subjected to after slaughter. For beef and lamb, employing chilling parameters that minimize cold shortening is of greatest importance and can be best addressed by ensuring that muscle temperatures are not below 10°C before pH reaches 6.2. For pork, because of the impact of high muscle temperatures and low pH on the development of pale, soft, and exudative (PSE) pork, a more rapid chilling process is needed to reduce PSE with the recommended internal muscle temperature of 10°C at 12h and 2-4°C at 24h. Spray chilling, a system whereby chilled water is applied to carcasses during the early part of postmortem cooling, is used to control carcass shrinkage and to improve chilling rates through evaporative cooling. Delayed chilling can be used to reduce or prevent the negative effects of cold shortening; however, production constraints in high-volume facilities and food safety concerns make this method less useful in commercial settings. Electrical stimulation and alternative carcass suspension programs offer processors the opportunity to negate most or all of the effects of cold shortening while still using traditional chilling systems. Rapid or blast chilling can be an effective method to reduce the incidence of PSE in pork but extreme chilling systems may cause quality problems because of the differential between the cold temperatures on the outside of the carcass compared to the warm muscle temperatures within the carcass (i.e., muscles that are darker in color externally and lighter in color internally).     

Electrical stimulation and ultra-rapid chilling of pork

Six pigs were stimulated at 5 min post mortem and six remained unstimulated. All the pigs were split hot and one side from each pig was rapidly chilled in two stages (air at -40°C and 1 m/s for 80 min followed by 0°C and 0·5 m/s for 130 min) and the other side was conventionally chilled (air at 0°C and 1 m/s for 24 h). The weight loss from rapidly chilled sides was approximately 1% less than that from conventionally chilled controls. Cooked samples of Longissimus dorsi were tougher from unstimulated rapidly chilled sides (0·23 J) than from unstimulated conventionally chilled sides (0·18 J), whilst samples from both stimulated treatments were significantly more tender (0·15 J). These differences in toughness are thought to be due to a combination of cold shortening and lack of conditioning. The average pH in the longissimus dorsi of both rapidly and conventionally chilled stimulated sides at 50 min post mortem was 5·57 and samples from these muscles were slightly paler and more watery than the unstimulated controls.     

Effect of chilling applied to suckling lamb carcasses on hygienic,physicochemical and sensory meat quality

The effect of post mortem temperature treatment on suckling lamb carcass and meat quality was study. Conventional (2 °C for 24 h), ultra-rapid (− 20 °C for 3.5 h, 2 °C until 24 h) and slow chillings (12 °C for 7 h, 2 °C until 24 h) were compared. Total viable counts (TVC), weight losses, and pH and temperature falls were recorded on carcasses. Meat colour, water holding capacity (WHC), Warner-Bratzler shear force, sarcomere length and sensory analysis were evaluated in M. longissimus. Ultra-rapid treatment reduced TVC and weight losses. The pH decline was faster in slow chilled carcasses than in faster chilled carcasses. No significant differences were found for colour and WHC. Slow treatment carcasses showed significantly lower shear force and higher sarcomere length. In the sensory analysis, tasters also rated the early post mortem slow-treated meat as more tender, less fibrous and chewy. Therefore, delay chilling in suckling lamb carcasses made it possible to obtain meat with better organoleptic characteristics, without affecting weight loss or hygienic quality.     

Effect of chilling applied to suckling lamb carcasses on hygienic, physicochemical and sensory meat quality

The effect of post mortem temperature treatment on suckling lamb carcass and meat quality was study. Conventional (2°C for 24h), ultra-rapid (-20°C for 3.5h, 2°C until 24h) and slow chillings (12°C for 7h, 2°C until 24h) were compared. Total viable counts (TVC), weight losses, and pH and temperature falls were recorded on carcasses. Meat colour, water holding capacity (WHC), Warner-Bratzler shear force, sarcomere length and sensory analysis were evaluated in M. longissimus. Ultra-rapid treatment reduced TVC and weight losses. The pH decline was faster in slow chilled carcasses than in faster chilled carcasses. No significant differences were found for colour and WHC. Slow treatment carcasses showed significantly lower shear force and higher sarcomere length. In the sensory analysis, tasters also rated the early post mortem slow-treated meat as more tender, less fibrous and chewy. Therefore, delay chilling in suckling lamb carcasses made it possible to obtain meat with better organoleptic characteristics, without affecting weight loss or hygienic quality.     

The effect of ultra-rapid chilling and subsequent ageing on the calpain/calpastatin system and myofibrillar degradation in lamb M. longissimus thoracis et lumborum

The effect of ultra-rapid chilling (-20°C) on the proteolytic degradation of myofibrillar proteins during ageing, by the calpain/calpastatin system in lamb was investigated. Carcasses (36) were ultra-rapidly chilled (-20°C for 3.5 h followed by 20.5 h at +4°C) or chilling at +4°C for 24 h. After chilling all carcasses were stored at +4°C for a further 4 days. Samples of M. longissimus thoracis et lumborum were taken for Warner-Bratzler shear force measurement, sarcomere length, SDS-PAGE and enzyme activity analysis. Ultra-rapid chilling (-20°C) had no effect on the proteolytic degradation of myofibrillar proteins by the calpain/calpastatin system compared to conventional chilling (+4°C). However, no difference in tenderness was found between the two chilling regimes at 1 or 5 days postmortem so differences in myofibrillar degradation or enzyme activity would not be expected.     

Electrical stimulation of rabbit and lamb carcasses.

Electrical stimulation of rabbit and lamb carcasses at voltages of 250 V, pulsed at 15 Hz, resulted in a rapid immediate fall of pH and a sustained rate of fall 2–3 times greater than normal. The ATP level falls in step with the pH; at about pH 6.2, 50% of it has disappeared and at pH 5.7, more than 90%. In lamb carcasses rigor onset in the major muscles of fore-, hind-limbs and back occurs 4–5 h earlier than the normal 5–7 h and rigor is complete at least 4 h earlier. As a result, it is safe to cool or freeze stimulated lamb carcasses within 3 h of slaughter, compared with the need to delay at least 10 h with normal carcasses to ensure that cold- or thaw-contracture will not occur with subsequent toughening of the meat.     

Use of electronic probes for classifying lamb carcasses

Three commercially available electronic lamb carcass grading probes (Hennessy Grading Probe, AUS-Meat Sheep Probe, Swedish FTC Lamb Probe) and one developmental probe (Ruakura GR lamb probe) were assessed for accuracy and suitability for use on-line on the lamb dressing chain for objectively classifying lamb carcasses. GR is the total tissue thickness over the 12th rib taken at a distance 11 cm from the mid-line, used to define fatness in lamb carcass grading in New Zealand. Probe measurements were compared with manually measured GR (sometimes used at present) and Toland probe measurements (total tissue depth between the ribs) for accuracy of predicting both GR on the right side of the carcass and also carcass water (indicating muscle) and fat content. Probes were tested on six occasions, each having approximately 50 lambs. All probes combined with carcass weight accounted for over 70% of the variation (R(2)) of GR right, with GR left accounting for 92% of the variation of GR right. Inclusion of a quadratic probe term was not quite as useful as inclusion of carcass weight for predicting GR right. The three commercial electronic probes individually when combined with carcass weight could account for 36-49% of the variation in the percentage of water and fat in the carcass, with the manual GR probe (right) on the chilled carcass accounting for 55% of the variation in water and 58% of the variation in fat percentages. Chilled carcass measurements are expected to give better results than readings on hot carcasses. The use of a quadratic probe coefficient instead of carcass weight with the probe readings gave similar accuracy of prediction of carcass composition. There was little difference between the two sides in the accuracy of prediction. Small differences were found between regressions relating probe readings to GR and composition for the different probing occasions. The electronic probe results from this trial are consistent with overseas results where probes are in use for objectively grading the carcasses of meat animals.     

Characteristics of lamb carcasses of contrasting subjective muscularity

In order to compare characteristics of lamb carcasses with superior muscularity (the European E class) with carcasses that did not fit the E specification, 114 E carcasses were individually matched for weight and fatness class with 114 Non-E carcasses. The carcasses (mean WEIGHT = 17 kg) were processed under commercial conditions into six trimmed, boneless cuts of the leg and saddle (inside, outside, knuckle, rump, striploin and tenderloin) and two bone-in cuts (hind-shank and 7-rib rack). After adjustment for carcass weight, fatness (as assessed by fat depth C and tissue depth GR) and sex, the E-class group, relative to the Non-E group, had a 4.3% higher yield of leg and saddle cuts, a 14.2% higher leg muscularity index calculated from the weights of trimmed boneless cuts around the femur and femur length, a 13.6% higher muscle to bone ratio in the femur region, an 8.2% greater ‘eye’-muscle depth (B), and a 3.7% greater ‘eye’-muscle width (A) (all P < 0.001). All boneless cuts except the knuckle were heavier for the E group. Carcasses of female lambs had legs with higher muscle to bone ratios and a higher yield from the leg plus saddle (both P < 0.01), but the muscularity index was similar between sexes. It is concluded that although lamb carcasses subjectively selected as having higher muscularity will yield slightly more meat, this difference will be small compared with the greater muscle depth relative to bone length. The importance consumers attach to carcass or cut shape over and above any association with meat yield needs to be assessed.     

Development of a quality classification system for lamb carcasses

A total of 1660 commercial lambs, with slaughter weights ≥ 32kg and having no more than two permanent incisors, were selected on the basis of age, weight, gender, and fatness to be representative of the Canadian market lamb population and utilized to develop a quality classification system for lamb carcasses. Based upon the findings obtained, lamb should be defined as carcasses from ovines weighing 32 kg live or more and with no more than two permanent incisors. Mutton should be defined as carcasses from ovines with more than two permanent incisors or carcasses from ovines that have lost their third temporary incisor. Milk-fed lamb should be defined as carcasses from ovines weighing less than 32kg live. Consequently, classification recommendations arising from the present study apply only to carcasses from ovines defined as lamb, according to the previous definitions. Thus, lamb carcasses so defined can be effectively segregated into three quality groups based upon expected consumer acceptance, utilizing simple, subjective evaluations of the breakjoints and ribs, as follows: Group 1 possessing very red and moist breakjoints and round, red ribs, Group 2 possessing slightly red to red breakjoints and oval shaped ribs, which are either slightly red or have traces of red colour, and Group 3 possessing white, dry breakjoints and flat, white ribs. Classification of lamb carcasses on this basis will allow compensation to producers based upon carcass merit, reflecting consumer acceptance. Although availability and consumer demand will ultimately determine price premiums and/or discounts, based upon present findings, Group 1 should contain 9% or less of the lamb carcasses being marketed and should receive a premium to compensate for a higher degree of consumer acceptance. Group 2 should contain 75% or more of the lamb carcasses being marketed and should receive prevailing market value. Group 3 should contain 15% or less of the lamb carcasses being marketed and should receive a discount to compensate for a lower degree of consumer acceptance.     

Reduction of bacteria on pork carcasses associated with chilling method

In addition to reducing the temperature of pork carcasses immediately after slaughter and before fabrication, blast chilling (snap chill) or conventional chilling can reduce bacterial populations associated with fresh meats. However, there is little information on bacteria survival resulting from the freeze or chill injury of meat products. In this study, porcine fecal slurries with and without pathogens (Listeria monocytogenes, Salmonella Typhimurium, and Campylobacter coli) were inoculated onto skin-on and skin-off pork surfaces and subjected to industry-specific blast or conventional chilling conditions. A thin agar layer method was used for the recovery of freeze- or chill-injured cells. Test results indicated that there were no statistically significant (P > 0.05) differences between blast and conventional chilling treatments with respect to the reduction of high and low inoculation levels of mesophilic aerobic bacteria, total coliforms, or Escherichia coli on either skin-on or skin-off surfaces. Chilling treatments did not differ significantly (P > 0.05) with respect to their ability to reduce low (3 log10 CFU/cm2) levels of L. monocytogenes and Salmonella Typhimurium. However, C. coli was reduced to undetectable levels, even after enrichment, on pork surfaces inoculated with low levels (3 log10 CFU/cm2) and subjected to blast chilling. Blast and conventional chilling treatments were more effective against all pathogenic bacterial populations when pork surfaces where inoculated at high levels (5 log10 CFU/cm2). The effects of chilling techniques on microbial populations could provide pork processors with an additional intervention for pork slaughter or information to modify and/or improve the chilling process. The information obtained from this study has the potential to serve as a means of producing a microbiologically safer product.     

The use of dual-energy X-ray absorptiometry to estimate the dissected composition of lamb carcasses

A total of 140 male and female Dorset and Suffolk lambs were slaughtered according to four live weight classes (36-39kg, 41-44kg, 46-49kg and 51-54kg). Total tissue, fat and lean masses, and bone mineral content measured by dual-energy X-ray absorptiometry (DXA) were used to predict dissected tissue weights. The DXA total weights accurately predict half-carcasses and primal cuts weights (shoulder, leg, loin and flank) (R(2)>0.99, CVe<1.3%). The prediction of the half-carcass dissected fat percentage is weaker (R(2)=0.77, CVe=10.4%). Fatness prediction accuracy is equivalent for the shoulder, leg and loin (R(2) between 0.68 and 0.78, CVe between 10% and 13%). The R(2) obtained when predicting dissected lean content from DXA variables is 0.93 for the half-carcass and higher than 0.83 for all cuts other than flank (CVe are between 3.5% and 6.5%, except for the flank, which is 9.1%). The prediction of bone weight using the bone mineral content is not very accurate for the half-carcass, shoulder and leg (R(2): 0.48, 0.47 and 0.43; CVe: 10.2%, 12.0% and 11.6%, respectively). The situation improves, however, for the loin (R(2)=0.70, CVe=10.7%). In conclusion, DXA is an effective technology for predicting total weight and the amount of lean and fat in lamb carcasses and their primal cuts.     

Importance of airborne contamination during dressing of beef and lamb carcasses

Carcasses along slaughter lines were exposed to normal slaughterhouse air or ultraclean air provided from a unit fitted with a HEPA filter. In cattle slaughterhouses, aerobic viable counts were measured by sponging the brisket at the end of the line to determine whether the slaughterhouse air had led to contamination of the carcasses. Furthermore, a replica cattle carcass with settle plates attached was exposed to similar conditions. The greatest contamination of the plates occurred at the hide puller (P < 0.01). The use of ultraclean air reduced the deposition of organisms onto settle plates (P < 0.01). The airborne route contributed to contamination in cattle slaughterhouses, but other vectors were more important. Further study of contamination of the brisket, at the time that it was first exposed, showed that knives transfer contamination from the hide. The use of ultraclean air at this position showed that the airborne route was a contributor to contamination (P < 0.1), but it was not the greatest vector. In lamb slaughterhouses, the highest counts on settle plates were found at the fleece puller (P < 0.05). The highest counts on the lamb carcasses were found on the brisket exposed from the start of the line to just after the fleece puller (P < 0.05). There was no clear relationship between the measured counts and the concentration of organisms in the air, indicating that the airborne route in lamb slaughterhouses contributes less to carcass contamination than do the surface contacts.     

Effect of chilling shrinkage of pig carcasses on yield of Wiltshire bacon

Summary. Twenty pig carcasses were taken fresh from the slaughterline and split into two sides. One-half of each pig was quick-chilled and the other rapidly chilled. Trimming, brine injection and curing were closely controlled and weights at various stages of processing were accurately measured.
Overall, there was no difference in the final weight of bacon produced by the two chilling systems. There was some variation in the curing weight loss of different pigs, pH appearing to be a factor.     

Microbial contamination occurring on lamb carcasses processed in the United States

Lamb carcasses (n = 5,042) were sampled from six major lamb packing facilities in the United States over 3 days during each of two visits (fall or winter, October through February; spring, March through June) in order to develop a microbiological baseline for the incidence (presence or absence) of Salmonella spp. and for populations of Escherichia coli after 24 h of chilling following slaughter. Samples also were analyzed for aerobic plate counts (APC) and total coliform counts (TCC). Additionally, incidence (presence or absence) of Campylobacter jejuni/coli on lamb carcasses (n = 2,226) was, determined during the slaughtering process and in the cooler. All samples were obtained by sponge-sampling the muscle-adipose tissue surface of the flank, breast, and leg of lamb carcasses (100 cm2 per site; 300 cm2 total). Incidence of Salmonella spp. in samples collected from chilled carcasses was 1.5% for both seasons combined, with 1.9% and 1.2% of fall or winter and spring samples being positive, respectively. Mean (log CFU/cm2) APC, TCC, and E. coli counts (ECC) on chilled lamb carcasses across both seasons were 4.42, 1.18, and 0.70, respectively. APC were lower (P < 0.05) in samples collected in the spring versus fall or winter, while TCC were higher in samples collected in the spring. There was no difference (P > 0.05) between ECC from samples collected in the spring versus winter. Only 7 out of 2,226 total samples (0.3%) tested positive for C. jejuni/coli, across all sampling sites. These results should be useful to the lamb industry and regulatory authorities as new regulatory requirements for meat inspection become effective.     

A probe to measure GR in lamb carcasses at chain speed

The GR (total tissue thickness at the twelfth rib, 110 mm from the midline) was measured with the AUS-MEAT sheep probe (ASP) on lamb carcasses at chain speed by an abattoir operator in two experiments, both at the same abattoir. In both experiments, GR was also measured on the carcass by an independent operator using a GR knife. For experiment 1, a total of 779 lamb carcasses were measured over four occasions and for experiment 2 data on 607 lamb carcasses were obtained on two occasions, twelve months after experiment 1. In both experiments, one operator measured the manual GR and a different operator used the ASP. A new version of the ASP was used in the second experiment. In only 30% of cases in experiment 1 did the operator probe at the correct rib, and in the majority of cases the thirteenth rib was used as the probing site. In only a small percentage of cases (2%) was the operator more than one rib away from the twelfth rib. In 67% of the cases for experiment 1, the operator probed at the correct site with respect to distance from the midline. Models were developed to describe the relationship between the manual and ASP GR measurements. In experiment 2, the amount of variation in manual GR explained by ASP measurements was greater than that in experiment 1 (R(2) = 0·80 compared with 0·72), and the accuracy of the estimates was significantly increased (± 1·54 mm compared with 2·31 mm). The better over-all performance of the ASP in the second experiments was indicated by the fact that for 90% of the sample the ASP measurements were within ±2 mm of the manual GR measurements whereas, for experiment 1, the level was less than 70%. Measurement time (day), which could be described as an operator 'effect', was identified as an important factor influencing the accuracy of GR estimates but location of the probed site with respect to the GR site was not found important. The significance of operator training and monitoring is discussed on the basis of the results, as are the implications of the findings for objective purchasing systems.     

Mineral composition of lamb carcasses from the United States and New Zealand

The mineral composition-iron (Fe), zinc (Zn), copper (Cu), calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), fluoride (F), and phosphorus (P) (New Zealand lamb only)-of lean tissue from lamb retail cuts was studied. Twenty-four US lamb carcasses of different ages (5 to 11 months), geographical regions (Texas, Colorado and Montana) and USDA quality grades (Prime and Choice) and 27 New Zealand lamb carcasses from three weight groups (11 to 12·5 kg, 13 to 14·5 kg, and 16·5 to 18 kg), age rangining from 7 to 8 months, were selected for use in this study. Mineral concentrations were influenced more by retail cut and age than by quality grade or weigth group. Foreshank and shoulder cuts from both the US and New Zealand group consistently had the highest (P < 0·05) Zn content among the cuts. The K content of the muscle in US lambs increased as age increased, while the level of Ca and Zn in New Zealand lambs decreased as carcass weight increased. Except for Ca, the mineral concentrations of the lean tissue from US lambs were higher than the New Zealand lambs, although the differences were not always significant. US lambs had approximately 20%, 30% and 37% more Fe, Zn and Mg, respectively, but 27% less Ca than lean tissue from the New Zealand lambs.     

Composition and sensory evaluation of lamb carcasses used for the traditional Mexican lamb dish, "barbacoa"

The objective of this study was to determine the differences in carcass characteristics and sensory attributes of "barbacoa" (a traditional Mexican lamb dish), both of imported (New Zealand) and domestic lambs in Mexico. A total of 28 carcasses from Pelibuey, Pelibuey×Suffolk and imported lambs were used. Carcass composition was determined by dissection of primal cuts from the left half of each carcass. The "barbacoa" from each ovine group was prepared separately in order to perform a consumer sensory evaluation for aroma, taste and tenderness. Results showed that imported lambs had larger carcasses, greater fatness and had better conformation than national lambs. There was no difference between groups in terms of lean tissue percentage (muscle+others) or in total carcass fat. The sensory attributes of the "barbacoa" did not differ among breeds. Pelibuey lambs (rustic, prolific and adaptable to the wide variety of Mexican climates) show competitive production performance in relation to specialized breeds.