Effect of early post-mortem cooling on temperature, pH fall and meat quality in pigs

The aim of this study was to investigate how early cooling of carcasses after slaughter by showering with cold water affected the rate of the pH fall post mortem, protein denaturation and drip loss. Eighty pigs were selected in pairs at debleeding according to sex and farm of origin. All pigs were halothane genotyped and glycolytic potential in LD analysed. One of each pair was cooled 30 min post mortem by showering with 10-12 °C water for 12 min. The control pig was treated normally except for the same delay before batch chilling commenced. The initial pH fall in LD and BF did not depend on the glycolytic potential in LD but at 5 to 6 and 24 hr post mortem pigs with the lowest glycolytic potential had the highest pH. Weight and lean meat content did not affect the cooling curve, i.e. the temperature fall. The results showed that it was possible to reduce the temperature in BF and LD by cooling at slaughter. The maximum difference in temperature between control and cooled carcasses 2hr post mortem was 2 and 1 °C in LD and BF respectively. The lowering of the muscle temperature early post mortem resulted in a reduced rate of the pH fall and a higher pH from 2 to 6 hr in the cooled carcasses. The rate of the pH fall in LD and BF seemed to be independent of temperature at levels above approximately 37 °C, but decreased linearly as the temperature dropped below approximately 37 °C. The cooling procedure used here did not result in a significant reduction in protein denaturation or drip loss, although there was a tendency towards lower drip loss in LD and BF in cooled carcasses.     

The effect of stress during lairage and stunning on muscle metabolism and drip loss in Danish pork

The effect on meat quality of a low stress handling system (LSS) compared with a traditional handling system (TS) was investigated in Duroc×(Landrace×Yorkshire; n=117) and (Hampshire×Duroc)×(Landrace×Yorkshire) pigs (n=110) under commercial conditions. In the low-stress handling system the pigs were kept in groups of 15 during lairage and movement up to the stunner. Before the stunner the groups were divided into three groups of five pigs for the CO(2)-stunning in a specially designed set-up. The pH and temperature were determined in m. longissimus dorsi (LD) and m. biceps femoris (BF) at various times post mortem. Immediately after exsanguination a biopsy was taken from the LD and analysed for the concentration of glycogen, lactate and creatine phosphate. The day after slaughter the pH was determined in the LD, BF, m. semimembranosus (SM) and m. semispinalis capitis (SC). The temperature was determined in the LD and BF, the internal reflectance was determined in the LD, SM and BF, the colour was determined in LD, the drip loss was determined in LD and BF, and the amount of blood splashing/bruising was evaluated in LD. There was a tendency for a higher concentration of creatine phosphate in the LSS-group (P=0.06). The pH in both the LD and BF on the day of slaughter decreased more slowly from 5 min post mortem to 40 min post mortem in the LSS-group than in the TS-group (P<0.001). From 40 min to 6 h post mortem the rate of the pH decline was similar in the two groups producing the lowest pH-level in the TS group. The day after slaughter the pH was similar in the two groups in the LD and SC, whereas in the BF and SM it was lower in the LSS-group than in the TS-group. The drip loss was lower in the LSS-group in both LD (P<0.01) and BF (P<0.05) whereas the internal reflectance was only different in LD with the lowest value in the LSS-group (P<0.001). The lightness (L*) was higher in the LSS-group (P<0.05). There was no effect of stunning system on the amount of blood splashing/bruishing in the LD. The study showed that by using a low stress stunning system it is possible to decrease drip loss, possibly by increasing the concentration of creatine phosphate and thereby delaying the acceleration of pH fall in muscles after death.     

Effects of housing conditions of slaughter pigs on some post mortem muscle metabolites and pork quality characteristics

The results of two experiments studying the effects of housing conditions on post mortem muscle metabolism and meat quality are presented. In the first experiment slaughter pigs (n=71) from two different crossings, were raised at a density of 0.7 m²/animal (10 pigs/pen) either with (enriched) or without (conventional) a bedding of daily fresh straw. In the second experiment, animals (n=60) were reared under either conventional or free range housing (1.25 m²/animal, 30 pigs per pen) conditions. Main differences between conventional and enriched housed pigs were found in the biceps femoris (BF) muscle, and related to temperature, drip loss and colour. Association studies revealed that there were significant correlations between early (0–4 h) post mortem muscle pH and glycogen and lactate concentrations and between muscle pH measured at 1 h post mortem and muscle rigidity, expressed as the rigor value. There were significant differences with respect to meat quality and post mortem metabolism of the longissimus lumborum (LL), between conventional and free-range pigs. Early post mortem pH (0–4 h) was highest in the free-range pigs, due to low lactate concentrations. The relatively fast pH decline in the conventionally housed group resulted in increased amounts of water exuding from the meat, as measured by the filter paper method. The ultimate pH, was lowest in the free-range animals. The differences in ultimate pH, however, had no effect on drip or cooking losses. It can be concluded from these results that enrichment of the housing system has little effect on the course of the post mortem metabolism and meat quality. However, increasing the freedom of movement by applying lower stocking densities, affects the post mortem muscle metabolism, resulting in reduced water exudation. Correlations up to 0.7 between energetic parameters are not sufficiently high to be useful to predict meat quality of individual carcasses.     

Effectson carcass weight and meat quality of pigs dehaired by scalding or singering post-mortem

Two experiments were designed to compare the effects of two pig dehairing techniques. In the first experiment, 120 pigs were slaughtered in the same abattoir in five weekly sereis. One half of each series was dehaired by singeing (the usual technique in this abattoir), while the other half was dehaired in a scalding-dehairing combination. In the second experiment, 48 pigs were slaughtered in two series, one-half of each series in an abattoir practising singeing, the other half in an abattoir practising scalding. Temperature and pH were measured 30 min after slaughter in the longissimus lumborum. Meat quality was assessed the day after slaughter in various muscles. One ham was cured and cooked, while the other one was processed by dry-curing. In both experiments, carcass weights and yields were noticeably higher after singeing. Hams were heavier in singed carcasses, but their proportions in the carcasses were little or not at all affected by the dehairing technique. Proportions of loins, shoulders and bellies were similar with both dehairing techniques. The dehairing technique affected neither temperature nor rate of post-mortem pH fall. Meat quality as assessed on fresh meat was slightly better in singed carcasses. Weights of cooked ham and dry ham per side were higher in singed carcasses, due to the higher initial ham weight, but processing yields were not affected by the dehairing technique.     

The influence of elevated temperature conditioning on bison (Bison bison bison) meat quality

Elevated temperature conditioning (ETC: 10°C until 10 h post mortem) was effectively employed as a means of cooling bison carcasses in order to avoid the cold-induced meat quality defects that are a risk with conventional bison carcass chilling (0-2°C for 24 h). The ETC treatment maintained internal M. Longissimus lumborum and M. Semimembranosus temperature above 10°C within the first 10 h post mortem. The time/temperature combination did not result in significant evaporative loss, although loss of weight during carcass cooling can represent a practical economic loss. ETC accelerated post-mortem glycolysis and pH decline, and resulted in samples of lighter, more intense red colour than those conventionally chilled. Significant improvement in both initial tenderness and tenderization during ageing was realized with the use of ETC.     

Initial chilling rate of pre-rigor beef muscles as an indicator of colour of thawed meat

The effect of three rigor temperatures and two muscles of different fibre composition on the colour of thawed meat were determined. Within 45 min post-mortem, m. semitendinosus (ST) and m. biceps femoris (BF) from unstimulated heifer sides were held at 0, 10 and 35°C until they entered rigor. The rate of pH fall was higher at 35°C than at 0 and 10°C; and the pH values were lower (first 12 h post mortem) in the ST than the BF. Hunter L*, a* and b* and the hue angle increased with increasing rigor temperature (P<0.001). The ST was lighter and yellower and had greater hue angle than the BF. Colour parameters were plotted against the rate of muscle cooling in the first hour post mortem and linear regression lines were fitted to the data and equations were derived that gave a good indication of the colour and colour stability of the muscles as meat.     

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.     

Procedure for determination of glycolytic potential in porcine m. longissimus dorsi

The aim of this work was primarily to work out a procedure for removal of samples from LD for determination of glycolytic potential in connection with experiments at commercial abattoirs and secondly to determine the correlation between glycolytic potential and ultimate-pH in Danish pigs. Samples of LD were taken immediately after exsanguination and 30 h post mortem. All samples were analysed for the content of glycogen, glucose, glucose-6-phosphate and lactate to be able to calculate the glycolytic potential. The results showed no difference in glycolytic potential in LD irrespective of sampling time. Samples removed after exsanguination contained a higher amount of glycogen and less lactate than samples removed the day after slaughter, where most of the glycogen had been transformed into lactate. These results show that samples for determination of glycolytic potential in LD can be removed the day after slaughter in the chilling room instead of being removed immediately after sticking at the slaughter line, which is less practical and hygienic. There was a significant correlation (-0.61) between glycolytic potential in LD and ultimate pH in LD.     

The effect of electrical stimulation on the quality of three bovine muscles

Meat bulls were randomly assigned to five treatment groups-intermittent electrical stimulation at 300 V (ES) at 5 min and 35 min post mortem (intact carcasses), 35 min post mortem (split carcasses) and non-stimulated controls (NS) (intact and split carcasses). Stimulated carcasses in all groups showed a significantly more rapid pH fall during the first 8h post mortem in adductor (AD), longissimus dorsi (LD) and triceps brachii (TB) muscles. Cooling rates were relatively slow. Samples were removed from the carcass at 24h post mortem. After vacuum storage at 3°C for 6 days stimulated muscles showed lower drip (LD and TB) and heating loss (TB), lower shear force values (AD, LD and TB) and higher taste panel scores (AD, LD and TB) compared with NS controls. No significant differences in tenderness were observed between the three ES groups. Sarcomere length assessment showed more contraction in NS carcasses, particularly in the superficially located LD and TB. These results suggest that cold shortening may occur in some muscles under cooling conditions so far considered safe in this respect. Since higher drip losses coincided with lower sarcomere lengths in these (NS) muscles, it is suggested that, under these conditions, ES may mask the increased drip losses which are possibly the result of muscle contraction. Furthermore, ES prevents the occurrence of cold shortening and, in addition, may exert some 'extra tenderising effect', which is not related to splitting of the carcass nor restricted merely to the LD muscle.     

Perspective of NIRS measurements early post mortem for prediction of pork quality

The potential of near-infrared spectroscopy (NIRS) measurements early post mortem was investigated to predict ultimate drip loss, colour, tenderness and intra-muscular fat of pork. Three locations (M. longissimus thoracis, M. longissimus lumborum and M. semimembranosus) in 102 pig carcasses were tested at the end of the slaughter line. A priori variation in pork quality was introduced using an experimental design covering: genotype, lairage time, pre-slaughter handling and day of slaughter. At 1 h post mortem a diode array VIS/NIR instrument (Zeiss MCS 511/522, 380-1700 nm) equipped with a surface fibre optic probe was used and at 1 day post mortem ultimate pH, drip loss, colour and shear force was measured on similar locations. Results indicated that it was possible to predict intra-muscular fat content (correlation (R(2) of 0.35 with multiple linear regression), standard error of prediction (SEP)=3.6 g/kg), but the configuration has to be refined for on-line application (bigger aperture). For drip loss no correlation was achieved with the PLS method. Even extremes (low drip loss (<2.5%) or high drip loss (>4.5%)) in drip loss were not discriminated. Predicting drip loss with NIRS early post mortem is not successful, although NIRS in the slaughter line has potential as a fast predictor of intra-muscular fat. Possibilities for using the NIRS technique to get to know more about muscle metabolism and post mortem changes are promising.     

The influence of exhaustion and electrical stimulation on the meat quality of young bulls: Part 1-Post-mortem pH and temperature

After designing a method of handling cattle so that they reproducibly developed DFD meat, pH and temperature in cattle developing DFD and normal meat, respectively were studied. The influence of low voltage stimulation on both groups was also investigated. Depending on final pH and other characteristics of the meat, the carcasses could be assigned to subgroups representing pronounced DFD, slight DFD and normal meat, with and without electrical stimulation. In normal and in pronounced DFD carcasses electrical stimulation speeded up the pH drop but did not affect the final state of the meat. In stressed animals the pH values are variable for the first few hours post mortem. This effect is enhanced by electrical stimulation which, in carcasses with slight DFD (from stressed but not exhausted animals), may produce extremely fast pH drop and PSE-like meat. There is no evidence that electrical stimulation would influence the incidence of DFD in cattle slaughtered under commercial conditions. In normal animals electrical stimulation raised the carcass temperature during the first few hours post mortem by approximately 2°C. Carcasses from stressed animals had a higher temperature, independent of stimulation.     

Chilling pig carcasses: Effects on temperature, weight loss and ultimate meat quality

Effects of conventional (4°C, air velocity 0·5 m/s) and forced chilling at -5°C (120 min) or -30°C (30 min) with air velocities of 1, 2 or 4 m/s, followed by conventional chilling till 24 h post mortem on temperatures, meat quality and weight losses, were studied. Experiments were carried out in six batches of six slaughter pigs each (crossbred gilts, weighing 105-110 kg. The subcutaneous temperature decreased very rapidly to values below 0°C when 'ultra' rapid chilling (-30°C) at high air velocities (4 m/s was used. Immediately after rapid chilling, when the carcasses were railed into a conventional chiller, the subcutaneous temperature increased above the air temperature, after which the decline in temperature was continued. Temperature inside the biceps femoris muscle decreased from the start of chilling rather slowly according to an asymptotic curve until ultimate values of 4°C were reached. Theoretically calculated temperatures during slaughter and chilling were comparable with the measured values; indicating that a finite-element calculation method in combination with a cylindrical model for heat transport can be used to predict muscle temperatures for various chilling regimes. Losses in carcass weight, 24 h after conventional and forced chilling at -5°C, were about 2%. After 'ultra' rapid chilling (-30°C) the losses were reduced to 1·3% when air velocity was increased to 4 m/s. Meat quality of the longissimus lumborum muscle was not significantly affected by the various chilling regimes except for the variables related to tenderness. The Warner-Bratzler shear forces were higher (P < 0·05) together with shorter sarcomere lengths (P < 0·10) after 'ultra' rapid chilling at a high (4 m/s) air velocity, indicating an increased risk of cold shortening.     

Tenderisation of lamb meat: Effect of rapid postmortem temperature drop on muscle conditioning and aging

Lamb Longissimus dorsi muscles were excised from carcasses of 9-12 kg and 16-20 kg weight and brought to internal temperatures of either 0°C, 4°C, 10°C, 15°C, 20°C or 36°C within 3-4h post mortem. After rigor completion they were allowed to age at 4°C for 7 days. Sensory panel scores obtained on the first day of post-rigor aging showed that meat from heavier animals was tougher than that of lighter ones at any temperature. In all cases aging for 7 days had a marked tenderising effect which was similar at all studied temperatures, and greater in heavier animals. Tenderness was also dependent on the temperature at conditioning, as shortening caused by either high or low temperature resulted in meat toughening. The sole and surprising exception to this fact was, however, the high sensory scores obtained in 0°C experiments, even though shortening occurred as expected. In fact, a more intense proteolysis was evident in this case, which was already apparent on the first day of aging. The effect of a rapid drop of muscle temperature to 0°C on the fast and intense proteolysis, capable of even overcoming toughness due to cold shortening, was explained by the higher pH and the dramatic increase of the sarcoplasmic Ca(++) level induced early post mortem by chilling and which might result in the activation of calpain.     

The effects of spray-chilling carcasses on the shrinkage and quality of beef

After slaughter, alternate beef carcass sides (left, right) were allocated to an intermittent spray-chilling cooling treatment using water (4 cycles per hour; 60 s/cycle) and conventional air chilling (1-2°C; air velocity 0·5 m/s), or conventional air chilling only. Experiments 1, 2, and 3 (n = 19, 26 and 16 carcasses) involved spray-chilling for 4, 8, 12 h in shrouded sides, whereas experiment 4 (n = 16 carcasses) involved 8 h of spray-chilling in unshrouded sides. At 24 h post-slaughter all sides were ribbed (12 13 th ribs ), and assessed for meat and fat colour. Half the treatment and control sides in each experiment were aged for 6 days, while the boneless ribs and inside rounds were removed from the remaining sides, vacuum packaged and held for 6 days. After 6 days of storage, retail packs of rib steaks and round roasts were prepared and assessed for colour and drip losses over a 4-day period. Spray-chilling significantly reduced carcass shrinkage at 24 h post slaughter in experiments 1-4 by 0·48, 0·69, 0·89 and 1·48%, respectively. After 6 days of cooler storage, spray-chilling significantly reduced carcass shrinkage in experiments 3 and 4 only (0·47 and 0·94%). Weight and drip losses for vacuum packaged ribs and inside rounds were not influenced by spray-chilling over 6 days of storage. Spray-chilling had no influence on rate of pH decline, but reduced loin and round muscle temperatures by 1-2°C. Loin eye muscle colour and shear force were not affected by treatment, but in experiments 2, 3 and 4, fat colour was significantly lighter in spray-chilled compared to conventionally chilled sides. Colour changes and drip losses in retail packs over 4 days for rib steaks and round roasts were not related to spray-chilling. It was concluded that spray-chilling could provide a moderate reduction in carcass shrinkage during cooling without having a detrimental influence on muscle quality.     

Sensory and meat quality traits of pork in relation to post-slaughter treatment and RN genotype

The effects on eating quality and meat quality of two different forms of post-slaughter treatment, performed in an abattoir, were studied in carriers and non-carriers of the RN(-) allele. Carcasses were subjected to rapid and slow chilling, and pelvic and Achilles suspension in a factorial experimental design. A temperature of 10?°C was achieved in the centre of M. longissimus dorsi (LD) within 3.5 h in rapidly chilled carcasses and within 8 h in slowly chilled carcasses. In deep M. semimembranosus (SM) a temperature of 10?°C was achieved within 11.5 h in rapidly chilled carcasses and within 14 h in slowly chilled carcasses. LD from slowly chilled RN(-) carriers suspended by the pelvis exhibited the greatest tenderness, while LD from rapidly chilled non-carriers suspended from the Achilles tendon exhibited the lowest tenderness. Pelvic suspension or slow chilling of non-carriers produced the same improvement in tenderness, and when combined the tenderness increased further. However, the tenderness of the RN(-) carriers was already high, and no significant improvement was seen following any of the studied post-slaughter treatments. Pelvic suspension prevented shortening of muscle fibres, as seen by longer sarcomeres in LD from pelvic-suspended sides. However, longer sarcomeres were associated with greater tenderness only in LD from non-carriers of the RN(-) allele. The presence of the RN(-) allele and a slow chilling regime increased the rate of pH decline in LD. Achilles suspension also increased the rate of pH fall in SM, in addition to the RN(-) allele and slow chilling. The overall tenderness of LD was mainly related to the course of pH decline during rigor; lower pH values between 3 and 7 h post-mortem contributing to greater tenderness. The myofibrillar length was predominantly related to RN genotype and was shorter in RN(-) carriers than in non-carriers. The RN(-) allele and slow chilling contributed to higher evaporation losses and RN(-) carriers exhibited increased frequency of PSE meat in the ham muscles. The use of pelvic suspension appears advantageous over slower chilling, since it improved tenderness without any negative influence on drip loss, evaporation or cooking loss.     

Effect of different electrical stimulation and chilling treatments on pork quality

The effect of different chilling and electrical stimulation (ES) treatments on the carcass and eating quality of pork has been examined. Preliminary trials (Study I), with a variety of ES treatments, indicated that, on the basis of pH fall, drip loss and tenderness, the most effective was that using 700 V peak at 12·5 Hz for 90 s applied at 20 min post-slaughter. These ES parameters were used throughout the main study (II) using 80 pigs, one side of which was stimulated and the other not, before being chilled rapidly (10°C in deep loin within 2–3 h of slaughter) or conventionally (10°C in deep loin within 5 h of slaughter).

Changes in pH and temperature during chilling were observed and, after chilling, quality assessments on LD and Sm muscles included drip loss, muscle opacity and instrumental toughness at 3 days post-slaughter.

Electrical stimulation, 20 min post-slaughter, improved tenderness of the LD and, to a lesser extent, the Sm of rapidly chilled pig sides. This advantage was gained without producing PSE pork. In fact, drip loss from the LD was consistently less from the sides which had been stimulated.     

Studies of extra low voltage electrical stimulation of mature beef carcasses

The quality characteristics of biceps femoris (BF) and semimembranosus (SM) roasts obtained from mature cow carcasses treated with a commercial extra low voltage (30 V) electrical stimulation (LVES) system were determined. LVES was applied for either 2 (ESII) or 4 min (ESIII). Evaluations were conducted on meat obtained from control sides (no ES) aged for either 48 h (Ia) or 7 days (Ib) and from ES sides aged 48 h. ES caused a reduction (P<0·001) in pH values at 2 and 6 h post mortem. At 24 h, the pH of muscles from all carcasses was about 5·5. ES duration did not influence muscle pH. Rib-eye muscle colour for ESII and ESIII carcasses was lighter and brighter (P<0·05) than that of control carcasses. Generally stimulated BF roasts had greater cooking losses than control Group Ib roasts; SM roasts from ES carcasses had lower losses than comparable to Group Ib roasts. ES duration had no effect on per cent cooking losses. Trained panelists generally detected few significant effects in BF roasts due to ES. Warner-Bratzler data indicated that ESII and ESIII BF roasts were similar and significantly more tender than comparable control Group Ib samples: OTMS data indicated that all BF roasts were similar in tenderness. However, SM roasts from ES carcasses were judged more soft (Groups II and III) and tender (ESII) than comparable control roasts. Instrumental measurements of tenderness for SM roasts tended to support the taste panel results. Generally, duration of LVES had no effect on the eating quality of either BF or SM roasts. Since LVES effects on the palatability of SM roasts were evident but the effects of stimulation of BF roasts were few, further studies of this LVES system are needed before its use can be recommended. Generally, increasing post-mortem ageing time for mature control carcasses did not influence either BF or SM roast quality.     

Influence of rapid chilling on biochemical parameters governing the water‐holding capacity of pork longissimus dorsi

The aim of this study was to investigate the effects of rapid chilling (RC) of carcasses on the quality of pork longissimus dorsi (LD) compared to conventional chilling (CC). Carcasses subjected to RC were chilled at ?20 °C for 1.5 h and then moved to 4 °C until 24 h post‐mortem, while carcasses that were CC were placed directly in a chill at 4 °C for 24 h post‐mortem. RC accelerated the rates of temperature decline post‐mortem (P < 0.01) and increased pH values at 1.5 and 8 h post‐mortem (P < 0.05). RC could significantly decrease the denaturation of myosin and sarcoplasmic proteins during post‐mortem ageing. Samples of RC had a significant lower purge loss compared to CC group during post‐mortem ageing (P < 0.05). Our study implies that RC could influence the biochemical changes of pork LD which may further regulate water‐holding capacity during post‐mortem ageing.     

Potential interactions between the effects of preslaughter stress and post-mortem electrical stimulation of the carcasses on meat quality in pigs

The experiment examined the influence on pork quality of the electrical stimulation of carcasses from pigs subjected to different ante-mortem handling treatments. The carcasses were subjected to a slow chilling regimen to reflect less than ideal commercial practice. A total of 288 pigs (mean live weight 89 kg) of both sexes and a range of genotypes were used. They came from the Meat and Livestock Commission 's Pig Development Unit at Stotfold and were processed in 12 equal batches. Prior to slaughter they were transported for 2 h (80 km) at a stocking density of 0.5 m(2)/100 kg live weight. Preslaughter handling included being mixed or not with unfamiliar animals and being given a 3 h rest in lairage or not. One group received handling to simulate that in stunning races immediately before slaughter. There were no material interactions between the effects of ante- and post-mortem handling. Pigs rested 3 h in lairage had lower plasma cortisol levels irrespective of whether mixed with unfamiliar animals. Plasma lactate concentrations increased with greater ante-mortem stress. Pigs subjected to the simulated stunning race treatment had elevated carcass temperature. Greater ante-mortem stress progressively elevated pHu in the muscles and tended to reduce eating quality. Electrical stimulation followed by slow chilling raised initial muscle temperature, reduced pH(45) and pHu, and produced meat that was paler, had higher hue and saturation values and lost more drip during storage. Neither instrumentally-determined texture nor taste panel texture was affected, but electrical stimulation decreased juiciness and increased pork flavour. Overall eating quality was not affected by stimulation.     

The effect of high post-mortem temperature on the development of pale, soft and exudative pork: Interaction with ultimate pH

The effects of post-mortem temperature and ultimate pH (pH(u), 24 h post mortem) on the development of the pale, soft and exudative (PSE) characteristics in pig longissimus dorsi muscle were studied. Ten out of the 13 pigs used received pre-slaughter injections of adrenaline in order to deplete muscle glycogen stores. The two muscles from each pig were held at 12 or 35°C during rigor mortis development. Results from covariance analysis, using pH(u) as covariate, showed that a high temperature (35°C) resulted in a dramatic increase in internal light scattering (FOP) 24 h post mortem and a significant decrease in water- and salt-soluble proteins. Cooking loss, sarcomere length and drip loss did not vary significantly with rigor temperature. Interaction between temperature and pH(u) was estimated by assessing the relationship between pH(u) and the difference between the two rigor temperatures for selected traits. The best predictive model was a segmented quadratic model with a plateau which gave significant results for FOP, drip loss, water- and salt-soluble proteins. The effect of temperature decreased curvilinearly when pH increased until a constant value above which no noticeable difference was recorded (drip loss, water- and salt-soluble proteins) or a constant difference was reached (FOP). The pH values corresponding to the convergence points differed from one trait to another. They ranged from 5·72 to 6·22. These results illustrate the importance of muscle glycogen content at slaughter and subsequent pH(u) with regard to the development of temperature-induced PSE meat.