Effect of stunning conditions on occurence of PSE defects in hams of rn+/RN(-) pigs

Pigs of the same genetic type at the RN and HAL loci, i.e. rn⁺RN⁻/NN were reared in similar conditions of feeding and housing. They were slaughtered in two abattoirs (referred to as A1 and A2) using a mixture of air (30%) and CO₂ (70%), at a rate of 300 pigs per hour per slaughterline. One hundred and thirty-two pigs from 11 farms were slaughtered in A1 using a corusinga restrainer and 127 pigs from 5 farms were slaughtered in A2 with the backloading technique. pH at 40 min, 2.5 h and 24 h after slaughter and colour (L*, a*, b*) at 24 h after slaughter were measured in the semimembranosus muscle. Meat quality of the ham was scored as follows: 1, no PSE-zone; 2, doubtful; 3, PSE-zones in the semimembranosus and sometimes on the internal flexor muscles; 4, PSE-zones in all the flexor muscles. The muscle pH value was higher in A2 than in A1 at 40 min post mortem (P<0.01), but not at 2.5 and 24 h. L* (P<0.001) and b* (P<0.05) were higher in A1 than in A2. There was a remarkable difference in meat quality scores, with 50% of the hams scoring 3 or 4 in A1, vs 13% in A2. Lairage time before slaughter affected (P<0.01) the pH value at 2.5 h (5.69 vs 5.93). The values of pH1 and pH2.5 decreased with increasing the meat quality score. The values of L* and b* increased markedly with the score. The results of the present study indicate that the method of bringing the slaughter pigs to the stunning device affects the frequency and importance of PSE meat in the ham. The automated driving of groups of animals to the stunning machine combined with the backloading of a nacelle, compared to a traditional system driving pigs in single file using electrical goads and a restrainer was beneficial with respect to both meat quality and animal welfare.     

Enzymological investigations on the causes for the PSE-syndrome, I. Comparative studies on pyruvate kinase from PSE- and normal pig muscles

A fast breakdown of glycogen is observed in muscles of stress-susceptible pigs leading to pale, soft and exudative (PSE) meat. We report a comparative study of pyruvate kinase from muscles of normal and PSE-prone pigs. Compared with enzyme from normal muscle, pyruvate kinase isolated from PSE-muscle shows a five times lower K(m) for phosphoenol pyruvate and a more than ten times higher k (cat)K (m) value. The pH-dependency of the enzymatic activity is shifted to more acidic values for pyruvate kinase from PSE muscles. According to isoelectric focusing, pyruvate kinase from PSE muscle consists of three isoforms, while only two isoforms are detectable in pyruvate kinase preparations from normal pigs. The various isoforms were isolated by preparative isoelectric focusing and their steady-state properties were compared. Isoform 3, which is found only in PSE muscle, shows a 10-fold higher specific activity, a 30-fold lower K(m) value and a 100-fold increased k (cat)K (m) value for phosphoenol pyruvate compared to isoform 1. The presence of isoform 3 in PSE-muscle appears to be responsible for the high activity of this enzyme under the more acidic conditions prevailing in PSE-muscle. In vitro phosphorylation and dephosphorylation experiments using total enzyme and purified isoenzyme 1 suggest that isoforms 2 and 3 arise from isoform 1 by phosphorylation. Thus protein phosphorylation seems to be responsible for the shift in activity of pyruvate kinase, a key enzyme of glycolysis, under the acidic conditions of PSE-muscles.     

Effects of transportation time,distance, stocking density,temperature and lairage time on incidences of pale soft exudative (PSE) and the physico-chemical characteristics of pork

The study determined the effects of transportation time, distance, stocking density, temperature and lairage time on incidences of PSE and pork quality. Frequencies of PSE cases in stocking density categories within transport duration classes were determined. General linear models, regression and the principal component (PC) analysis were used to analyse the data. Highest incidences of PSE were recorded in autumn season while lowest incidences were recorded in the spring season. Transportation time and stocking density significantly affected pH_u and ultimately PSE incidences although there were no interactive effects. Highest risks of PSE occurrence were observed with more space allowance. The highest incidences of PSE were observed for animals that had travelled for two hours while the PSE cases were lower in animals that travelled for longer times. Distance travelled and transportation time had significant effects (P < 0.05) on thawing loss (TL) % of pork. No relationships were reported between the other pre-slaughter variables and pork quality attributes. With the exception of transportation time and distance travelled which had a positive relationship with TL%, variation in other pre-slaughter variables did not affect meat quality variables. The risks of PSE occurrence were dependent on stocking density and transportation time.     

Maintaining muscles at a high post-mortem temperature induces PSE-like meat in turkey

The aim of the present study was to validate an experimental model which surely generates pale, soft, exudative (PSE) turkey meat. Immediately after exsanguination, Pectoralis major (n=15) were kept at various temperatures (4, 20 or 40 °C) for 6 h. All the muscles were then stored at 4 °C for 9 days. They had the same rate of pH fall. L^* values were higher in the 40 °C treatment muscles than in the two other treatment muscles between 1 and 9 h. Drip loss of the 40 °C treatment muscles was higher than in the two other treatment muscles. However, thawing and cook loss were not significantly different between treatments. Cooked meat from the 40 °C treatment muscle was tougher than the two other treatment muscles. Napole yield was lower for these muscles. Myofibrillar protein extractability was lower in the 40 °C treatment muscle whatever the considered time. We showed that the 40 °C treatment muscles were similar to PSE muscles.     

猪PSE肉的预防和改进措施

全球肉类加工业对PSE猪肉的关注与日俱增,这类劣质肉具有较高的亮度值和较差的保水性,同时加工产品的品质显著下降。叙述了猪PSE肉预防措施和加工特性的相关改进措施。为冷鲜猪肉的生产、品质的改善提供理论依据和技术支持。     

Compound C, an inhibitor of AMP-activated protein kinase, inhibits glycolysis in mouse longissimus dorsi postmortem

Pale, soft, and exudative (PSE) meat has been recognized for decades and causes huge economic loss to the meat industry due to its inferior quality. Although it has been well established that fast and excessive glycolysis combined with high temperature in muscle early postmortem is the cause of PSE meat, the molecular mechanisms associated with this abnormal glycolysis remain poorly defined. Our previous studies with mice and pigs suggest that AMPK regulates muscle glycolysis postmortem. To confirm further the role of AMPK in the regulation of postmortem glycolysis, we investigated the effects of intraperitoneal injection of compound C, a specific AMPK inhibitor, on AMPK activation and glycolysis in postmortem longissimus dorsi (LD) muscle of mice. Data showed that intraperitoneal injection of compound C inhibited AMPK activation in postmortem mouse LD muscle. Simultaneously, injection of compound C inhibited glycolysis and increased muscle pH corroborating of our previous observations that postmortem glycolysis is inhibited in AMPK knockout mice. This study firmly supports that AMPK regulates glycolysis in postmortem skeletal muscle and suggests that AMPK can be a target to control postmortem glycolysis, preventing incidence of PSE meat.     

PSE肉的产生、鉴别和控制

猪的PSE肉发生率较高,PSE肉一般不受消费者欢迎。对PSE肉的概念、发生机理、产生的原因、鉴定以及控制措施作了介绍。     

正常肉和白肌肉的蛋白质变化

测定白肌肉(Pale,Soft,Exudative,PSE)和正常猪肉(Reddish-pink,Firm,Non-exudative)持水性指标和在宰后不同时间的蛋白溶解性和蛋白降解程度。结果显示:PSE肉的各种蛋白溶解性都显著低于正常肉(p<0.05),宰后4 h的总蛋白、肌浆蛋白和肌原纤维蛋白的溶解性与滴水损失和贮藏损失都呈显著负相关,与持水力呈显著正相关。正常肉和PSE肉的肌浆蛋白和肌原纤维蛋白的SDS-PAGE电泳条带存在差异,PSE肉早期伴肌动蛋白(Nebulin)含量明显低于正常肉。可见PSE肉肌原纤维的降解较快,宰后早期的蛋白溶解性可以用于预测猪肉的持水性。     

Biochemical and physicochemical properties of thermally treated natural actomyosin extracted from normal and PSE pork Longissimus muscle

Biochemical and physicochemical properties of thermally treated natural actomyosin (NAM) from normal and pale, soft and exudative (PSE) pork were studied. About 37% and 25% of available sulphydryl groups formed disulphide bonds or other permanent chemical bonds at 70 °C in NAM from normal and PSE pork, respectively. Surface hydrophobicities of NAM from normal and PSE pork at 70 °C were 3.6 and 2.4 times greater than that at 40 °C. About 90% of the α-helical structure of NAM was lost by heating to 70 °C. The temperature at maximum α-helical content decline of NAM was in accordance with the peak 3 thermal transition obtained by differential scanning calorimetry and the lowest storage modulus (G′) during thermal rheology. NAM from normal pork underwent aggregation with a higher extent of hydrophobic interaction and disulphide bonds, higher temperatures at maximum velocity for conformational change and unfolding than that from PSE pork. As a consequence, NAM from normal pork had superior rheological properties.     

Progress in reducing the pale, soft and exudative (PSE) problem in pork and poultry meat

Research in the area of the pale, soft and exudative (PSE) pork and poultry meat is reviewed in this article with an emphasis on genetic, biochemical and metabolic factors contributing to the problem. Over the past five decades, there has been much more work in the pork meat area where a few genetic markers have been identified, and are currently used to remove susceptible animals from the herd. Some of the markers are linked to aberrant calcium regulation in the early postmortem muscle. The poultry industry is still not at the point of using genetic marker(s); however, some recent work has revealed several potential markers. The review also discusses environmental factors such as antemortem stress and early postmortem processing practices (e.g. chilling rate) that can influence the development and severity of the PSE phenomenon. Some of these factors are known to cause protein denaturation at the early stage of postmortem and directly contribute to poor water-holding capacity and inferior texture in fresh meat and later in processed products. A newer hypothesis suggesting that variation in protein oxidation, in response to antemortem stress and early postmortem tissue environment, can contribute to development of PSE pork is also discussed. Finally, a few recommendations for future work are proposed.     

Phospholipase A2 and antioxidant enzyme activities in normal and PSE pork

In order to reveal the relationship between phospholipase A₂ and antioxidant enzymes and drip loss in pork, the study was designed to examine the effects of phospholipase A₂ and antioxidant enzymes on the water-holding capacity of pork during postmortem chilling. Six PSE and RFN samples (longissimus muscle) were used to determine the activities of phospholipase A₂ (tPLA_2, cPLA₂ + sPLA₂ and iPLA₂), superoxide dismutase (SOD) and GSH-Px, and acid phospholipase. The results showed that pH_1 h and pH_24 h from PSE pork were lower (p < 0.01) than for normal pork (RFN), but the L* value at 1 h and 24 h postmortem, TBARS content, drip loss at 48 h and 96 h, cooking loss, tPLA₂ activity and iPLA₂ were higher (p < 0.01) than of normal pork. Correlation analysis indicated that drip loss at 48 h was negatively related to pH_1 h (p < 0.01) and pH_24 h (p < 0.01) but positively to T_1 h (p < 0.01) and the activities of total phospholipase A₂ (p < 0.05) and calcium-independent phospholipases A₂ (p < 0.01). The tPLA₂ and GSH-Px play important roles in drip loss.     

The prevalence of PSE characteristics in pork and cooked ham — Effects of season and lairage time

A total of 180 pigs was slaughtered in the same slaughterhouse, but divided in six different trials distributed over Winter (December–March) and Summer (April–September). Meat quality measurements (pH, electrical conductivity, color and/or water-holding capacity) were carried out 30 min, 24 and/or 35 h after slaughter in three different muscles: M. gracilis, M. semimembranosus and M. longissimus dorsi. A tendency towards a higher proportion of PSE meat during Summer was found in the examined muscles. Moreover a higher protein, higher dry matter content, a lower water/protein ratio and a lower slicing yield were found for the cooked hams suggesting a higher PSE prevalence in the Summer. A lairage time between 2 and 4 h during Summer and less than 2 h during Winter was related to a lower proportion of PSE meat. The correlation coefficients between the individual meat quality variables were moderate, but showed the predictive power of the pH measured 24 h post-mortem in the M. gracilis for meat quality.     

Purification and isoenzymic composition of glycogen phosphorylase b from normal and abnormal (PSE) muscles

Ion exchange chromatography and preparative isoelectric focusing allowed the identification of five isoenzymes of glycogen phosphorylase b from the longissimus dorsi muscle of normal pigs and those prone to having pale, soft and exudative (PSE) muscle. The isoelectric point of the isoenzymes varied in the pH range from 6.29 to 6.55. One of them, with an isoelectric point at about a pH of 6.49, accounts for 65% of the total glycogen phosphorylase b activity. No significant differences between normal and PSE-prone pigs were observed in the total glycogen phosphorylase b activity and in the isoenzyme distribution pattern. It is concluded that the fast glycogen turnover in PSE-prone pigs is not due to a different isoenzyme pattern of phosphorylase b.     

Quality characteristics of Chinese sausages made from PSE pork

Chinese sausages made from normal and different levels of PSE pork (100% Normal, 50%Normal+50% PSE and 100% PSE) were vacuum-packaged and stored at 4 °C for 45 days. The composition, processing yield, pH value, thiobarbituric acid (TBA) value, water activity, lactic acid bacteria counts and sensory properties of the meat products were evaluated. PSE pork loins had lower pH value, water holding capacity, moisture, fat and myofibrillar proteins content, but higher L^* value, drip loss and protein content than normal pork. Sausages made from 100% PSE pork had lower pH value, processing yield, moisture and fat content, but higher protein content than those of the 100% Normal and the 50% Normal+50% PSE treatments. Water activity was higher in the 100% PSE treatment than in other treatments. No differences in lactic acid bacterial counts among these treatments were observed. The pH values and water activity of the meat samples decreased, while lactic acid bacterial counts increased with storage time. TBA values among these treatments were not significantly different; however, the increase% of TBA values was higher for the 100% PSE treatment. TBA values of all treatments remained relatively low during storage. Chinese sausages made with 50–100% PSE pork had lower sensory texture, flavor and overall acceptability scores than the control samples, but were of acceptable quality.     

Quality of meat and meat products produced from southern European pig breeds

Genetic and environmental effects on the quality of meat from southern European pig breeds are discussed. In the literature, it is evident that the breeds native to southern Europe have an interesting quality of products with respect to improved pigs. The free-range system increases the value of animal products due to the influence of outdoor rearing on the chemical, physical and organoleptic characteristics of the product. Traditional food products of high quality, such as those obtained from animals reared outdoor, are in high demand. The studies carried out on native pig breeds in southern Europe have focused on various aspects, ranging from studies of population genetics aimed at averting the danger of extinction and reducing inbreeding to studies of the factors affecting the quality of products. The purpose of this review is to analyse the literature on pig breeds native to southern Europe, with particular reference to the effects of genetics and breeding systems on the quality of products.     

High early post-mortem temperature induces activation of AMP-activated protein kinase and development of pale,soft and exudative characteristics in turkey muscles

This study investigated the effect of early post-mortem temperature on development of a turkey muscle's pale, soft and exudative (PSE) characteristics. Muscles obtained at 20 min post-mortem were incubated at 0, 20 and 40 °C until 4 h post-mortem and then stored at 4 °C. During incubation, the 40 °C group had greater rate of pH decline, lactate accumulation and R-values increase than other groups. Moreover, AMP-activated protein kinase (AMPK) activation at 1 h post-mortem was higher in the 40 °C group than the other groups. At 24 h post-mortem, the 40 °C group had higher L* values and drip loss; SDS-PAGE and western blotting indicated that lower protein solubility (sarcoplasmic, myofibrillar) in the 40 °C group resulted from phosphorylase denaturation and further adhere to myofibrillar fraction. These results suggest that high temperature early post-mortem could induce AMPK activation, which results in rapid glycolysis, thus affecting protein solubility and generating PSE characteristics.     

Updated estimates of HAL n and RN− effects on pork quality: Fresh and processed loin and ham

A 1000-pig F2 intercross QTL detection experimental population was generated using two commercial sire lines. Independent carriers of HAL n and RN− mutations (10% and 14%, respectively) were included in this population as control genotypes. The effects of HAL n and RN− heterozygous genotypes on fresh and transformed loins and hams were estimated using a mixed model methodology. The results document the unfavorable effects of both mutations on meat quality. Smaller effects of HAL Nn genotype compared to HAL nn or RN−rn+ genotypes were estimated. Interestingly, effects of HAL Nn genotype on meat pH and loin color could be insignificant at 24-h postmortem, but translate into higher water losses on storage and cooking, and result in tougher cooked loin. Using the same methodology, significant effects of the PRKAG3 (RN) I199 allele on ultimate pH values but not on glycolytic potential were observed.     

Carcass and meat quality traits of four different pig crosses

The study compared properties of Finnish Landrace × Yorkshire crossbred sows mated with Finnish Landrace (FL), Norwegian Landrace (NL), Norwegian Duroc × Norwegian Landrace (NDL), or Swedish Hampshire (SH) boars. The focus was to study the cross-sectional area of loin, cross-sectional area and number of muscle fibres, loin colour and pH value as well as the ratio of water to protein in the loin.The four studied crosses were quite similar having only small differences in carcass and meat quality. The carcass lean content was the lowest in NDL. The loins of FL and NL were longer than the loins of NDL and of SH. The cross-sectional area of loin was the largest in SH. The loin of FL was lighter in colour and the loin of SH was redder than the loins of the other crosses studied. The protein content was lower and the ratio of water to protein higher in loin of SH than in the other crosses.     

Effects of halothane gene and pre-slaughter treatment on meat quality and welfare from two pig crosses

Pigs from crosses of a Piétrain (Pi) and a Large White×Piétrain (LwPi) heterozygous (Nn) boar lines with Landrace×Large White homozygous negative (NN) sows, were used to study the effect of halothane gene and pre-slaughter treatment on animal welfare and meat quality. A total of 83 gilts (47 NN and 36 Nn) were assigned to a long treatment (3 h 15 min transport and 12 h lairage) and 73 (39 NN and 34 Nn) to a short treatment (30 min transport and 2 h lairage). Heart rate was recorded throughout loading and transport. Blood samples were collected before loading, after transport, and at exsanguination to measure cortisol, creatine phospho-kinase (CPK) and lactate dehydrogenase (LDH). Carcasses were classified and commercial cutting was carried out. Meat quality was assessed on the Longissimus thoracis muscle by measuring electrical conductivity (PQM), colour (Minolta CR 200 and Japanese scale) and ultimate pH. Loin drip losses were assessed at 24 h. Halothane carriers showed a higher increase in cortisol levels after transport and exsanguination in the long treatment (P<0.05) as well as in LDH and CPK after exsanguination in the short treatment (P<0.05). In this treatment, halothane-free pigs recovered during lairage when comparing LDH and CPK increases after exsanguination to their increases after transport. No effect of the halothane gene on heart rate was observed. Pi sired pigs were leaner and had higher yields of leg and loin compared with LwPi sired pigs (P<0.001), but no differences in meat quality were observed between crosses. Halothane carriers had a higher estimated lean content (P<0.01) and shoulder and leg yields (P<0.01), but poorer meat quality than non-carriers (i.e. higher incidence of PSE meat, P<0.001). Although pre-slaughter treatment and halothane genotype did not significantly affect pHu, significantly higher L*, a* and b* values found in the short treatment and Nn individuals indicated paler meat. These results suggest that for improving meat quality and welfare the halothane gene should be removed from breeding schemes.