Variations in chicken breast meat quality: implications of struggle and muscle glycogen content at death

1. Pectoralis major (P. major) muscle pH and meat quality traits were studied in relation to bird response to ante-mortem stress in three chicken lines: a fast-growing standard line (FGL), a slow-growing French 'Label Rouge' line (SGL) and a heavy line (HL). Ninety-nine birds of the three genetic types were slaughtered at their usual marketing age (6, 12 and 6 weeks for FGL, SGL and HL birds, respectively) on the same day. The birds of each line were divided into three different ante-mortem treatment groups: minimum stress (shackling for 10 s) (C), shackling for 2 min (SH) and acute heat plus shackling stress (exposure to 35 degrees C for 3.5 h and shackling for 2 min before stunning) (H + SH). 2. Regardless of chicken line, wing flapping duration (WFD) between hanging and stunning was strongly negatively related to P. major muscle pH at 15 min post-mortem. It was also moderately negatively related to P. major muscle glycolytic potential (GP), which represents glycogen level at death. Increasing WFD induced an increased ultimate pH (pHu) only in HL. The consequences of increased WFD for breast meat traits were dependent on the chicken line: it induced lower L* and b* and higher a* and drip loss in SGL while it only increased breast a* in HL birds. By contrast, WFD variations did not alter breast meat quality traits of FGL birds. Regardless of the chicken line, increased GP was associated with lower pHu and higher L* and drip loss. In SGL, it also increased b* and decreased curing-cooking yield of breast meat. 3. Struggling activity on the shackle line and muscle glycogen content at death could partly explain line and pre-slaughter variations in breast meat pH and quality traits. The water holding capacity of the raw and cooked meat was impaired by long shackling in the case of SGL birds while it was barely affected by ante-mortem conditions in the two standard lines. In conditions which minimised bird struggling (C), SGL and FGL birds had meat with a better water holding ability than that of broilers from the heavy line. However, when broilers were subjected to SH or H + SH conditions, the breast meat water holding capacity of SGL birds was lowered to the same level as that of the heavy line birds.     

Preslaughter stress and muscle energy largely determine pork quality at two commercial processing plants

The objective of the present experiment was to study physiological changes elicited in response to stress in the immediate preslaughter period and to link them to pork quality characteristics. Crossbred, halothane-free pigs (n = 192) were processed in eight groups (24 pigs per group) on various days at one of two commercial processing plants operating different stunning systems (electrical and CO2 stunning in Plants A and B, respectively). In each group, half the pigs were exposed to either minimal or high preslaughter stress. Blood samples were taken at exsanguination, and lactate, cortisol, and catecholamines, as well as blood pH and temperature, were assessed and linked to various longissimus muscle quality attributes. Additionally, muscle pH and temperature were measured 30 min postmortem, and muscle glycolytic potential was determined 22 h postmortem. At both processing plants, high preslaughter stress resulted in higher (P < 0.05) blood cortisol and lactate; however, the effects of preslaughter stress on catecholamines and blood pH were believed to be biased by the different stunning methods employed at the plants. High preslaughter stress increased (P < 0.05) blood temperature at Plant A but not at Plant B. At both plants, high stress increased (P < 0.05) 30-min muscle temperature and decreased (P < 0.05) 30-min muscle pH. Ultimate pH was increased (P < 0.05) and muscle glycolytic potential was decreased (P < 0.05) by high preslaughter stress. At both plants, high stress resulted in inferior pork quality attributes (P < 0.05), including reflectance, electrical conductivity, filter paper moisture, drip loss, and L* value. The effect of stress was greater on water-holding capacity than on pork color, with drip losses increased by 56%. Of all stress indicators measured at exsanguination, only blood lactate was strongly correlated with pork quality attributes. Regression analyses revealed that blood lactate and glycolytic potential accounted for 52 and 48% of the variation in drip loss and L* value, respectively. In combination with high preslaughter stress, high glycolytic potentials were related to increased drip losses. We conclude that high preslaughter stress leads to impaired pork quality, with high muscle energy levels aggravating the negative effects of preslaughter stress. Monitoring stress level by blood lactate measurement in combination with strategies to control muscle energy present at slaughter may help to improve meat quality.     

Post mortem muscle metabolism and meat quality in three genetic types of turkey

1. A standard (FG, fast-growing), a black local or 'label', type (SG, slow-growing) turkey line, and the crossbreed between these two lines were compared for muscle post-mortem metabolism and related meat quality traits. 2. Ninety male turkeys (30 of each genetic type) were raised under the same experimental conditions until slaughter at 16 weeks of age. 3. Live weights at 16 weeks of age differed significantly (7.8, 6.0 and 4.2 kg, for the FG, crossbred and SG lines, respectively). Collagen content of Pectoralis superficialis (PS) muscle was higher in SG birds than in the other two types. 4. The rate of post-mortem glycogen depletion and lactate accumulation in PS and Ilio tibialis (IT) muscles were similar in the 3 lines, as were the rate and extent of post-mortem pH fall in PS muscle. In IT muscle, however, SG birds showed a slight but significantly faster pH decline. 5. Colour measurements indicated a paler breast muscle and a higher degree of myoglobin oxidation in SG birds at 24 h post mortem, than in both other lines. But these differences had disappeared after 4 and 7 d post mortem 6. SG birds showed higher drip loss and instrumentally-assessed toughness in breast muscle, compared with crossbred and FG birds. FG birds, however, had the lowest yield of breast meat after curing-cooking. 7. No marked differences in post-mortem metabolism were found between the three lines. However, differences in water-holding capacity of fresh and cured-cooked meat suggest that factors other than the rate and extent of post-mortem pH fall may contribute to the respective characteristics of these lines.     

Relationships between behavioral and meat quality characteristics of pigs raised under barren and enriched housing conditions.

In this study the effects of barren vs enriched housing conditions of pigs on their behavior during the lairage period (2-h holding period before slaughter), carcass characteristics, postmortem muscle metabolism, and meat quality were studied. The barren housing system was defined by common intensive housing conditions (i.e., with slatted floors and recommended space allowances), whereas the enriched environment incorporated extra space and straw for manipulation. Salivary cortisol concentrations were measured before transport and at the end of the lairage period. During the lairage period the percentage of time spent walking and fighting by the pigs was registered. Carcass characteristics such as weight, meat percentage, and backfat thickness were determined. At 5 min, 45 min, 4 h, and 24 h postmortem, pH, temperature, and lactate concentrations were determined in the longissimus lumborum (LL) and biceps femoris (BF) muscles. Capillarization of the muscle, mean muscle fiber area, and color and drip loss after 2 and 5 d of storage were determined for both muscle types. Pigs from the barren environment had a significantly higher increase in cortisol from farm to slaughter, but no differences in behavior were observed during the lairage period. Carcass characteristics did not differ between pigs from barren and those from enriched housing conditions. Postmortem lactate formation was significantly lower in LL muscles of enriched pigs at 4 and 24 h postmortem. Capillary density and mean muscle fiber area did not differ between the groups of pigs. The percentage of drip loss at 2 and 5 d after storage of LL muscle samples from enriched-housed pigs was significantly lower than that of the barren-housed pigs. Similar tendencies were found for the BF muscle from pigs kept in an enriched environment, but these were not statistically significant. The housing system did not affect meat color. It is concluded that on-farm improvement of animal welfare by environmental enrichment can also lead to beneficial economic effects after slaughter by improving the water-holding capacity of pork.     

Postmortem interactions of muscle temperature, pH and extension on beef quality

The effect of pH, temperature and structural damage of muscle early postmortem on the quality of beef, particularly tenderness, was examined in a randomized complete block design with a 2 x 2 x 2 factorial. Semitendinosus muscles were excised from the right sides of 64 Charolais crossbred steer carcasses, placed in a restraint device in a controlled environment and subjected to high (31 degrees C) or low (20 degrees C) temperature, high (control) or low (electrically stimulated) pH and restraint at excised length or restraint at 125% of excised length for 15 min early postmortem. Temperature, pH, shrink, drip loss, cooking loss, sarcomere length, fragmentation index, shear force, color reflectance and collagen and protein solubilities of the muscles were measured after 7 d of aging at 2 degree C. High-temperature aging increased fragmentation index and color reflectance and decreased protein solubility (P less than .05). Decreasing pH via electrical stimulation increased sarcomere length of the muscles aged at the high temperature only (P less than .05). Extension of muscles prior to aging lowered shear force values of the low-temperature muscles compared with the high-temperature muscles (6.12 vs 7.84 kg, SE .38). Stimulation of the muscles also decreased collagen solubility in the high-temperature, extended muscles. Although postmortem temperature and pH were the factors that influenced meat quality most, early postmortem extension should be considered as a modulating variable of meat tenderness.     

Influence of increasing slaughter age of chickens on meat quality, welfare, and technical and economic results

Because of the increasing demand for raw cuts and processed products, there is a trend to producing very heavy broilers. Breeds that are used for such kinds of production have been intensively selected for growth rate and breast meat yield, and birds are reared for a longer period than standard broilers. This study was to evaluate the effects of increasing slaughter age on technical and economic factors, including production efficiency and environmental costs, bird welfare, and breast meat quality in a modern heavy broiler line. Five groups of 300 male Ross 708 chickens were reared until slaughter ages of 35, 42, 49, 56, or 63 d. Increasing age at slaughter from 35 to 63 d resulted in a 7.4-fold increase (P < 0.01) in mortality rate (5.21 vs. 0.70%). It also increased (P < 0.001) the slaughter weight and ADFI of birds 2.5- and 1.4-fold, respectively, without affecting their G:F. Under our experimental conditions, economic profit evaluated through the net gain reached a maximum at 42 d. The moisture and ammonium content of litter increased (P < 0.05 and P < 0.01, respectively) rapidly during rearing concomitantly with increased (P < 0.05) occurrence and severity of contact dermatitis and decreased (P < 0.05) walking ability and activity of birds. Thermal comfort also decreased (P < 0.05) greatly as early as 42 d of age. Changes in carcass quality occurred mainly between 35 and 56 d of age, with a progressive increase (P < 0.001) in breast and leg yield, whereas body fatness was barely affected by age. Major changes in breast meat traits were observed between 35 and 49 d of age, with an increase in muscle pH at 15 min (P < 0.01) and 24 h (P < 0.001) postmortem and reduced (P < 0.001) lightness and drip loss. The protein and lipid content of raw breast meat also increased (P < 0.05 and P < 0.01, respectively) with age. Taking into account the main aspects of sustainability, we could recommend slaughtering chickens of heavy line at 42 d of age.     

Meat quality traits and muscle characteristicsin high or low fear lines of Japanese quails (Coturnix japonica) subjected to acute stress

1. The influence of acute stress before slaughter on muscle and meat quality was studied in adult male quail from lines divergently selected for long (LTI) or short (STI) duration of tonic immobility (TI) and from the unselected (C) control line. 2. When subjected to acute stress, birds from the long TI line responded differently to those of the control or the low fear lines. LTI birds exhibited: a higher plasma creatine kinase and a smaller increase in plasma corticosterone levels, a higher pHu and drip loss values for breast meat associated with no differences in L*a*b* colour values; a higher percentage of fast glycolytic myofibres (IIb) and correspondingly (correlate) higher glycolytic (activity) in the pectoralis major (PM) muscle, and consequently lower oxidative enzyme activity in the PM muscle. 3. It is concluded that acute stress affected muscle metabolism differently in the STI, C and LTI lines. Hence, selection for TI, which is correlated with underlying fearfulness, can indirectly lead to differences in meat quality.     

母体日粮低能量对后代肉仔鸡生长性能、胴体品质和肉质的影响

本文旨在研究母体日粮低能量对后代肉仔鸡生长性能、胴体品质及肉质的影响.试验选用低脂系肉种鸡120羽,随机分成2组,每组60个重复,每个重复1羽,即单笼饲养.在肉种鸡产蛋期产蛋率达到5%进行试验处理,试验分试验组和对照组,试验组代谢能量为对照组的80%孵化后的肉仔鸡按照母体不同能量处理各挑选健康仔鸡,在相同的试验条件下进行饲养,试验期为56 d.结果表明:1)与对照组相比,母体日粮低能量有降低1日龄肉仔鸡体重的趋势,对全期日增重和料重比影响不显著(P＞0.05);2)与对照组相比,母体日粮低能量对后代肉仔鸡胸肌和腿肌的水分、脂肪和蛋白质含量,胸肌率和腹脂率均无显著影响(P＞0.05),但显著增加腿肌率(P＜0.05);3)与对照组相比,母体日粮低能量对后代肉仔鸡胸肌和腿肌的pH、红度、黄度、滴水损失和蒸煮损失均无显著影响(P＞0.05),但pH、红度和黄度值有升高趋势,滴水损失和蒸煮损失有降低趋势,胸肌和腿肌剪切力显著降低(P＜0.05);4)与对照组相比,母体日粮低能量显著提高后代肉仔鸡胸肌和腿肌肌纤维密度(P＜0.05),显著降低后代肉仔鸡胸肌和腿肌肌纤维直径(P＜0.05).本试验的研究结果表明:母体日粮低能量对后代肉仔鸡的胴体品质及肉质能产生一定的影响.     

Modulation of glycogen and breast meat processing ability by nutrition in chickens: effect of crude protein level in 2 chicken genotypes

The aim of the study was to evaluate the impact of 2 isoenergetic growing diets with different CP (17 vs. 23%) on the performance and breast meat quality of 2 lines of chicken divergently selected for abdominal fatness [i.e., fat and lean (LL) lines]. Growth performance, breast and abdominal fat yields, breast meat quality parameters (pH, color, drip loss), and muscle glycogen storage at death were measured. Increased dietary CP resulted in increased BW, increased breast meat yield, and reduced abdominal fatness at slaughter regardless of genotype (P < 0.001). By contrast, dietary CP affected glycogen storage and the related meat quality parameters only in the LL chickens. Giving LL chickens the low-CP diet led to reduced concentration of muscle glycogen (P < 0.01), and as a result, breast meat with a higher (P < 0.001) ultimate pH, decreased (P < 0.001) lightness, and reduced (P < 0.001) drip loss during storage. The decreased muscle glycogen content observed in LL receiving the low-CP diet compared with the high-CP diet occurred concomitantly with greater phosphorylation amount for the α-catalytic subunit of adenosine monophosphate-activated protein kinase and glycogen synthase. This was consistent with the reduced muscle glycogen content observed in LL fed the low-CP diet because adenosine monophosphate-activated protein kinase inhibits glycogen synthesis through its action on glycogen synthase. Our results demonstrated that nutrition is an effective means of modulating breast meat properties in the chicken. The results also highlighted the need to take into account interaction with the genetic background of the animal to select nutritional strategies to improve meat quality traits in poultry.     

Negative effects of stress immediately before slaughter on pork quality are aggravated by suboptimal transport and lairage conditions

The objectives of the present experiment were 1) to study the effects of transport conditions and lairage duration on stress level, muscle glycolytic potential, and pork quality; and 2) to investigate whether the negative effects of high stress immediately preslaughter are affected by preceding handling factors (transport and lairage). In a 2 x 2 x 2 factorial design, halothane-free pigs (n = 384) were assigned to either short (50 min) and smooth or long (3 h) and rough transport; long (3 h) or short (<45 min) lairage; and minimal or high preslaughter stress. Pigs were processed in eight groups (48 pigs per group) on various days at a commercial plant. Blood samples were taken at exsanguination to measure plasma cortisol and lactate concentrations. Muscle pH and temperature were measured at 30 and 40 min, respectively, and both were measured at 3 h, postmortem. A LM sample was taken 135 min postmortem to estimate glycogen content and rate of glycolysis. Pork quality attributes were assessed 23 h postmortem. Short transport increased cortisol when followed by short lairage (transport x lairage; P < 0.01). Long transport, but not lairage (P > 0.30), tended to increase (P = 0.06) muscle glycolytic potential. Long transport tended to increase (P = 0.08) electrical conductivity, and decreased a* (P < 0.01) and b* (P < 0.02) values. Decreasing lairage from 3 h to <45 min decreased (P < 0.05) the L* value, but it did not (P > 0.10) affect other pork quality traits. High stress decreased (P < 0.001) muscle glycolytic potential, and increased (P < 0.001) plasma lactate, cortisol, muscle temperature, rate of pH decline, and ultimate pH. Except for decreased (P < 0.001) b* values, pork color was not (P > 0.40) affected by high stress, but water-holding properties (measured by electrical conductivity, filter paper moisture, and drip loss) were impaired (P < 0.001) by high stress. Fiber optic-measured light scattering and Warner-Bratzler shear force were not (P > 0.12) affected by any treatment. Comparisons with the "optimal" handling (short transport, long lairage, and minimal stress) revealed that, with regard to water-holding properties, the negative effects of high stress were aggravated by suboptimal transport and lairage conditions. High stress alone increased electrical conductivity by 56%, whereas high stress in combination with short lairage led to an 88% increase. However, high preslaughter stress contributed most and was the major factor responsible for reductions in pork quality.     

Muscle characteristics and meat quality traits are affected by divergent selection on residual feed intake in pigs

Residual feed intake (RFI) is defined as the difference between the observed feed intake and that expected based on requirements for maintenance and production. A divergent selection was conducted during 4 generations in Large White male pigs to produce low and high RFI lines. The present study aims at determining the influence of this selection on biochemical and histological traits of skeletal muscle, and relating these changes to correlated effects on growth, carcass composition, and meat quality traits. At 8 d preslaughter, biopsies from the LM were taken in the fed state on 14 females from each RFI line fed ad libitum. Animals were slaughtered at 107.8 ± 8.0 kg of BW without any previous fasting. Samples of LM, semimembranosus (SM), biceps femoris (BFM), and rhomboideus muscles were taken at both 30 min and 24 h postmortem. Myofiber typing was only assessed in LM. Low RFI pigs ("efficient") had leaner carcasses with greater muscle content (P < 0.001), less backfat thickness (P < 0.001), and less intramuscular fat content in all 4 muscles (P < 0.01 to P = 0.04). Their greater muscle content was associated with hypertrophy of all fast-twitch fibers. Glycogen content in all glycolytic muscles (i.e., LM, SM and BFM), was greater in low than high RFI pigs. The greater accumulation of glycogen in LM of low RFI pigs was specifically located in the fast-twitch glycolytic IIBW fibers, which correspond to fibers containing IIb, IIb + IIx, or IIx myosin heavy chains. The difference in muscle glycogen content between RFI line pigs was more significant in the living animals (P = 0.0003) than at 30 min postmortem (P = 0.08). This was associated with a decreased ultimate pH (P = 0.001), and greater lightness of color (P = 0.002) and drip loss (P = 0.04) in LM of low than high RFI line pigs, suggesting that selection for reduced RFI may impair some meat quality traits, such as water-holding capacity. Pigs from the low RFI line exhibited a greater (P = 0.02) percentage of IIBW fibers in LM and tended (P < 0.10) to have less lipid β-oxidative capacity in LM, SM, and BFM. In contrast, no difference (P > 0.10) between lines was found for citrate synthase and lactate dehydrogenase activities, mitochondrial activity, and expression of genes coding for uncoupling proteins 2 and 3. Differences between RFI pigs in plasma leptin, cortisol, and thyroid hormone concentrations are presented and discussed. In conclusion, selection for low RFI influenced muscle properties in a way favoring muscle mass, but likely impairing meat quality.     

Glycolytic potential of red, soft, exudative pork longissimus muscle

Red, soft, exudative (RSE) pork is red as "normal" pork and exudative as PSE pork. The origin of RSE quality is unknown. In the present study, we determined whether the occurrence of RSE pork is related to the presence of the RN (Rendement Napole) gene. A glycolytic potential [= 2 x (glucose + glycogen + glucose-6-phosphate) + lactate] of > 180 micromol lactate/g of meat was used as indicator for presence of the RN gene. At 1 d postmortem, pork loin samples were collected at a commercial slaughter plant, and meat quality characteristics and glycolytic potential were determined. Glycolytic potential of RSE pork (n = 42) was higher (P < .01) than that of RFN (red, firm, nonexudative) pork (n = 25): 137 vs 110 micromol lactate/g of muscle. The glycolytic potential of PSE pork (n = 28) was 161 micromol lactate/g of muscle, which was higher (P < .01) than the glycolytic potential of RFN or RSE pork. Using a glycolytic potential of 180 micromol lactate/g of muscle as suggestive for the presence of the RN gene, four (10%) of the RSE samples were from RN carriers. By the same criterion, the PSE group contained nine (32%) RN gene carriers. These results suggest that the occurrence of RSE quality is not related to the presence of the RN gene.     

饲粮维生素E水平对43～63日龄黄羽肉鸡肉品质和抗氧化功能的影响

本试验旨在研究饲粮维生素E水平对43 ～ 63日龄黄羽肉鸡肉品质和抗氧化功能的影响.选用1 440只43日龄岭南黄羽肉公鸡,采用单因子随机分组试验设计,共设6个处理,每个处理6个重复,每个重复40只鸡.试验采用玉米淀粉-豆粕型基础饲粮,各处理饲粮营养水平除维生素E水平不同外,其他均相同.空白对照组饲喂未添加维生素E的基础饲粮,其余各处理饲粮中分别添加5、10、20、40、80 mg/kg维生素E.试验期21 d,试鸡地面平养,自由采食颗粒料和自由饮水.结果表明:1)饲粮中维生素E添加水平对试鸡生长性能和胴体品质无显著性影响(P＞0.05).2)胸肌肉色的L*、a*、b *值和肌肉嫩度也未受饲粮维生素E添加水平显著影响(P＞0.05).添加各水平维生素E均显著提高了宰后45 min胸肌pH(P ＜0.05),添加5、10、40、80 mg/kg维生素E均显著提高了宰后24 h胸肌pH(P ＜0.05).添加20、40 mg/kg维生素E显著降低了宰后45 min胸肌滴水损失,添加5、10、40、80 mg/kg维生素E显著降低了宰后48 h胸肌滴水损失(P＜0.05).3)饲粮中添加不同水平维生素E对试鸡血清中丙二醛(MDA)含量和总超氧化物歧化酶(T-SOD)活性无显著性影响(P＞0.05),添加10、20 mg/kg维生素E使试鸡血清中谷胱甘肽过氧化物酶(GSH-Px)活性分别比对照组提高了27.51％、30.57％(P＜0.05).添加各水平维生素E均使试鸡肝脏中GSH-Px活性显著提高(P＜0.05),添加20、40、80 mg/kg维生素E均显著降低了肝脏中MDA含量(P＜0.05),显著提高了肝脏中α-生育酚含量和肌肉中T-SOD活性(P＜0.05).以上试验结果提示,饲粮中添加维生素E可提高43～63日龄黄羽肉鸡机体抗氧化功能,改善肉品质,且添加20 mg/kg效果较好.     

Effects of high-protein/low-carbohydrate swine diets during the final finishing phase on pork muscle quality

The aim of this study was to lower the glycogen stores in pork muscle in order to improve pork muscle quality by feeding an ultra-high-protein/low-carbohydrate (HIPRO) diet. Forty-eight barrows (average live weight = 92 kg) were assigned across five treatments and two replications (four or five pigs per treatment by replication combination). All barrows were fed a control diet (13.1% CP) until their assigned treatment began. A treatment was the number of days the barrows were fed the HIPRO diet prior to slaughter (0, 2, 4, 7, or 14 d). The HIPRO diet (35.9% CP) was 97% extruded soybeans. Daily feed intake and weekly live weights were recorded for all barrows. At-death blood glucose levels were determined. Muscle pH, temperature, and electrical impedance were measured in the longissmus lumborum and semimembranosus muscles at 45 min, 3 h, and 24 h postmortem. Glycolytic potential; Minolta L*a*b* values; visual scores for color, firmness, and marbling; water-holding capacity traits (drip loss, purge loss, and cooking loss); and Warner-Bratzler shear force values were determined in the longissmus thoracis et lumborum. Weight gain per day decreased the longer the pigs were fed the HIPRO diet (P < 0.05). Daily feed intake decreased during the 1st wk on the HIPRO diet but returned to near-control levels during the 2nd wk, which when coupled with the continued decreases in daily gain resulted in substantial decreases in feed efficiency during the 2nd wk on the HIPRO diet (P < 0.05). Blood glucose levels and glycolytic potentials were not lowered by feeding the HIPRO diet (P > 0.05); therefore, no differences in rate of pH decline or ultimate pH among dietary treatments were found (P > 0.05). Likewise, there were no differences among dietary treatments in any of the measured meat quality attributes (P > 0.05). Feeding barrows the HIPRO diet for a time period prior to slaughter decreased feed intake, rate of gain, and feed efficiency and was not effective at lowering glycolytic potential or improving pork muscle quality.     

Effects of muscle pH and chilling on development of PSE-like turkey breast meat.

1. Early post-mortem pH was used to identify PSE-like turkey meat, characterised by a low water-holding capacity and pale colour. In a commercial turkey processing facility, the pH value of turkey breast muscle was measured at 0, 9, 10, 14, 154, 231, and 246 min post mortem. 2. At 14 min post mortem, the carcases were separated into 3 pH classes: low (<5.70), medium (5.70 to 6.18), and high (>6.18). Low pH carcasses (<5.70) had higher drip loss(1.75%) than medium (0.81%) and high pH carcases (0.75%). Furthermore, high pH carcases (>6.18) had a lower L* value (darker) than low and medium pH carcases. 3. The effects of using CO2 'snow' on turkey breast muscle quality were also investigated. Light CO2 'snow' treatment (57 g snow/kg breast) and heavy CO2 treatment (113 g snow/kg breast) resulted in higher drip losses than the control no CO2 snow) group.     

Rapid chilling cannot prevent inferior pork quality caused by high preslaughter stress

The present experiment investigated whether increasing chilling rate could improve meat quality in pigs exposed to either minimal or high stress immediately preslaughter. Pigs (n = 192) were offspring of halothane-free lines. On various days, four groups of 48 pigs were processed at a commercial plant. Within each group, half the pigs were exposed to either minimal or high preslaughter stress. Before entering the cooler at 45 min postmortem, carcasses of both minimal and high preslaughter stress treatments were allocated randomly to either conventional (+4 degrees C for 22 h) or rapid (three-phase chilling tunnel: -15, -10, and -1 degrees C for 15, 38, and 38 min, respectively, followed by storage at 4 degrees C until 22 h postmortem) chilling. Temperature and pH were measured in the blood at exsanguination and in the longissimus lumborum (LL) and semimembranosus (SM) muscle at 0.5, 2.5, 4.5, 6.5, and 22 h postmortem. Meat quality attributes (water-holding capacity and objective color measurements) were assessed on the LL. Preslaughter stress level affected pH and temperature in both blood and muscle, with lower (P < 0.001) pH values and higher (P < 0.001) temperatures for pigs exposed to high vs. minimal stress. Rapid chilling led to a faster (P < 0.001) temperature decline regardless of preslaughter stress level. Rapid chilling did not (P > 0.05) influence the rate of pH decline in the LL muscle, but reduced (P = 0.061) pH decline in the SM. Rapid chilling, as opposed to conventional chilling, decreased (P < 0.05) electrical conductivity in the LL, regardless of preslaughter stress; however, it could not compensate for the detrimental effect (P < 0.05) of stress on drip loss, filter paper moisture absorption, and meat color (L* value). Results from the present study indicated that increasing chilling rate is not a suitable method to resolve pork quality problems caused by inadequate preslaughter handling.     

Combined effect of epinephrine and exercise on calpain/calpastatin and cathepsin B and L activity in porcine longissimus muscle.

The objective of the study was to improve the understanding of the relationship between the effect of epinephrine plus exercise and meat tenderness. The calpain, calpastatin, and cathepsin B + L activities and postmortem proteolysis in porcine longissimus muscle were studied. The muscle glycogen stores were depleted in five pigs by s.c. injection of epinephrine (.3 mg/kg) at 15 h antemortem and exercise on a treadmill (5 min, 3.8 km/h) immediately before slaughter. Antemortem injection of epinephrine and treadmill exercise resulted in higher ultimate pH (6.32 vs 5.66 in control) and decreased (P < .05) thaw loss, cooking loss, and shear force values. The muscle energy depletion treatment increased (P < .05) the muscle mu-calpain activity measured 42 min postmortem, and at 24 h mu-calpain activity was still approximately 50% greater in the high ultimate pH group. Also, as the ratio of mu-calpain to calpastatin increased (P < .01), the overall proteolytic potential of the calpain system were greater. These observations suggest that the muscle energy level may influence the activity of the calpain system in the living animal. The high ultimate pH group showed lower (P < .001) cathepsin B + L activity in the myofibrillar and the soluble fractions after 8 d of storage, suggesting that the increased ultimate pH increased the stability of the lysosomal membrane and thereby reduced the release of cathepsins from the lysosomes during storage. The SDS-PAGE showed increased (P < .001) degradation of a 39-kDa band in the epinephrine and exercise-treated samples. Degradation products at 30, 31, and 32 kDa were labeled by troponin-T antibody in western blot. An appearing 24-kDa band was identified as a troponin-I degradation product in western blot. The proteolytic degradation pattern of myofibrillar proteins during storage differed in control and treated samples, supporting the hypothesis that calpain-mediated proteolysis was affected after treatment, resulting in meat with high ultimate pH.