Protease activity and the ultrastructure of broiler chicken PSE (pale,soft, exudative) meat

The biological cause of broiler PSE meat seems to be an excessive release of Ca²⁺, promoted by a genetic mutation of ryanodine receptors located in the sarcoplasmic reticulum of skeletal muscle cells. Excessive Ca²⁺, associated with protein denaturation in meat, enhances protease activity and influences the functional properties of PSE meat. Twenty-four-hour post-mortemPectoralis major m. samples exhibited lower values for pH, water-holding capacity, and shear force than did control samples, in contrast to colour (L∗) and cooking loss values. Protease activity, measured as myofibril fragmentation index, presented higher values in PSE meat than in control samples. Ultrastructural examination revealed shrinking and depolymerisation of myofilaments and Z-lines disorganisation within the sarcomere in PSE meat. Intense calpain activity was also observed, indicating that the process may initiate at the filaments, because of protein denaturation, and spread through Z-lines, resulting in the collapse of the sarcomere structure.     

Particle size analysis of lamb meat: Effect of homogenization speed, comparison with myofibrillar fragmentation index and its relationship with shear force

The impact of homogenization speed on Particle Size (PS) results was examined using samples from the M. longissimus thoracis et lumborum (LL) of 40 lambs. One gram duplicate samples from meat aged for 1 and 5 days were homogenized at five different speeds; 11,000, 13,000, 16,000, 19,000 and 22,000 rpm. In addition to this LL samples from 30 different lamb carcases also aged for 1 and 5 days were used to study the comparison between PS and myofibrillar fragmentation index (MFI) values. In this case, 1 g duplicate samples (n = 30) were homogenized at 16,000 rpm and the other half (0.5 g samples) at 11,000 rpm (n = 30). The homogenates were then subjected to respective combinations of treatments which included either PS analysis or the determination of MFI, both with or without three cycles of centrifugation. All 140 samples of LL included 65 g blocks for subsequent shear force (SF) testing. Homogenization at 16,000 rpm provided the greatest ability to detect ageing differences for particle size between samples aged for 1 and 5 days. Particle size at the 25% quantile provided the best result for detecting differences due to ageing. It was observed that as ageing increased the mean PS decreased and was significantly (P < 0.001) less for 5 days aged samples compared to 1 day aged samples, while MFI values significantly increased (P < 0.001) as ageing period increased. When comparing the PS and MFI methods it became apparent that, as opposed to the MFI method, there was a greater coefficient of variation for the PS method which warranted a quality assurance system. Given this requirement and examination of the mean, standard deviation and the 25% quantile for PS data it was concluded that three cycles of centrifugation were not necessary and this also applied to the MFI method. There were significant correlations (P < 0.001) within the same lamb loin sample aged for a given period between mean MFI and mean PS (−0.53), mean MFI and mean SF (−0.38) and mean PS and mean SF (0.23). It was concluded that PS analysis offers significant potential for streamlining determination of myofibrillar degradation when samples are measured after homogenization at 16,000 rpm with no centrifugation.     

Proteolytic pattern of myofibrillar protein and meat tenderness as affected by breed and aging time

The effects of breed and aging time (1, 7, 14, 21 days) were evaluated on meat tenderness and on proteolysis in 24 young bulls from Romagnola × Podolian crossbreed, Podolian and Friesian breed. Shear force decreased with aging in all breeds and showed the highest values at 1 and 7 days in Podolian meat. Myofibrillar fragmentation index significantly increased in Podolian meat throughout aging whereas in Friesian and in Crossbreed meat it increased only in the first week. Proteolysis was investigated by SDS-PAGE and 2-dimensional electrophoresis showing a different quantity and expression profile of myofibrillar proteins among breeds. In all breeds a decrease of troponin-T and an increase of troponin-T derived polypeptides during aging were observed. The highest decrease of troponin-T together with the presence of fragments of MHC in Podolian meat during aging was an outcome of a more extensive proteolysis in this breed. Data suggest that tenderness and proteolytic changes during aging are related to animal's breed.     

Comparison of fresh beef and camel meat proteolysis during cold storage

The objective of this research was to determine the difference in myofibrillar fragmentation of camel meat and beef during postmortem aging. Semitendinosus muscle was excised at slaughter and muscle pH was measured at 6, 12, 24, 48, and 72h postmortem. Myofibril fragmentation index was measured on 1, 3, 5, and 7 days postmortem. Also, myofibrils isolated from semitendinosus muscles of camel and cattle at 1, 3, 5 and 7 days postmortem storage were analyzed using sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. Results showed that the camel semitendinosus muscle had significantly higher myofibril degradation values compared to that in beef which was supported by a difference in troponin-T degradation and appearance of a 30kDa band. Postmortem pH decline of camel meat was significantly slower than that of beef. This study demonstrated that the semitendinosus protease activity of camel meat was superior to that of beef, which may have been due to the difference in pH decline.     

Evaluating the profile of myofibrillar proteins and its relationship with tenderness among five styles of dry-cured hams

In order to investigate the relationship between profile of myofibrillar proteins and tenderness among 2 kinds of Chinese hams (Jinhua and Xuanwei) and 3 kinds of European hams (Iberian, Serrano and Parma), shear force, myofibril fragmentation index (MFI), SDS-PAGE, carbonyls content and Raman spectroscopy were investigated. The shear force and salt content of Chinese hams were significantly higher than that of European hams, while moisture content was lower than that of European hams (p < 0.05). MFI values and SDS-PAGE profile revealed that the degradation of myofibrillar proteins in Chinese hams was lower than in European hams. In addition, Chinese hams showed significantly higher carbonyls content and β-sheet content compared with European hams, indicated that proteins aggregation intensively inhibited the degradation of myofibrillar proteins in Chinese hams. These results indicated that the higher shear force in Chinese style hams could be attributed to the lower moisture content and limited proteolysis.     

The effect of growth rate during backgrounding and finishing on meat quality traits in beef cattle

The relationship between growth rate and meat tenderness was investigated in ≈7000 cattle from temperate and tropically adapted breeds, finished on either pasture or in a feedlot to one of three market weights. Growth rate was calculated from weaning to the beginning of finishing (backgrounding) and over the finishing period, for both contemporary groups and individuals within these groups. Shear force and compression of longissimus lumborum (striploin) and semitendinosus (eye round) were measured at two days ageing, and palatability of the striploin at 14 days ageing. Analyses assessed the importance of growth rate during backgrounding and finishing on both a within group and between group basis. Where significant in individual animals, increased growth rate resulted in more palatable or tender meat, but the results were not consistent between breed types, locations, or the two muscles sampled. The most consistent relationship was an increase in palatability of the striploin with increased growth rate during finishing. Increased growth rate of groups during backgrounding improved palatability consistently across breedtypes, finish and location, however most of this relationship was accounted for by difference in mean group age at slaughter.     

Carcass composition and yield of Alaskan reindeer (Rangifer tarandus tarandus) steers and effects of electrical stimulation applied during field slaughter on meat quality

Twenty six adult reindeer steers (>3 years old) were used in a study to evaluate the effect of electrical stimulation (ES) on the quality of hot-boned, rapidly frozen shoulder meat and of the striploin (M. longissimus, LD) from carcasses held at +3°C for 48h. Carcass yield and composition was determined from the left carcass half from which the shoulder meat was not removed. The shoulder meat was processed frozen into cubed, sliced or ground products. Proximate composition of the LD, meat color and water-holding capacity were very similar for the ES (n=15) and non-electrical stimulation (NES; n=11) groups. Ultimate pH and shear force values were significantly lower in the ES meat (LD), however a trained sensory panel could not detect differences between the two groups in any of the measured sensory attributes. Consumer preference tests demonstrated that ES increased tenderness in the cubed and sliced products made from field slaughtered reindeer shoulder meat. ES in combination with hot boning and processing of boneless frozen meat can be used in field slaughter systems for reindeer to improve meat quality and to increase the potential value of the carcass.     

Evolution of hydrophobic polypeptides during the ageing of exudative and non-exudative pork meat

Thirty-six carcasses from 6-month-old pigs were classified in different exudative groups based on measurements of pH_2h, pH_24h, the colour parameter L^* and drip loss. A fraction containing polypeptides between 66 and 21 kDa was analysed by reverse phase chromatography at 2-h post-mortem and the evolution of 8 polypeptide fractions followed during ageing and related to meat quality. Three polypeptide (fractions P2, P3 and P4) at 2-h post-mortem showed significant lowest area values in the dark firm and dry class. During ageing, the higher content of P4 in exudative meats at 8-h post-mortem could be due to activation of the cathepsin system. On the other hand, P3 and P4 increased in DFD meats during the first 96-h post-mortem probably due to higher calpain activity. Few differences in polypeptides were related to meat qualities although they are important as precursors of small peptides and free amino acids.     

The influence of seasonal temperatures on meat quality characteristics of hot-boned, m. psoas major and minor, from goats and sheep

Samples of psoas major and minor muscles were randomly collected weekly from 203 (99 hot and 104 cool seasons) Omani goats, 215 (106 hot and 109 cool seasons) Omani sheep, 212 (104 hot and 108 cool seasons) Somali goats, 242 (127 hot and 115 cool seasons) Somali sheep and 211 (110 hot and 101 cool seasons) Australian Merino sheep slaughtered at the Central Slaughterhouse in Oman to investigate the effect of season on meat quality. The collection period was during November 2004–October 2005 and divided into two seasons according to ambient temperatures and relative humidity. These were termed: cool season (average temperature of 21 °C and 59% relative humidity and hot season (average temperature of 35 °C and 47% relative humidity). Muscles collected during the hot season had significantly (P < 0.05) higher ultimate pH values (5.78) than those collected during the cool season (5.65). Myofibrillar fragmentation index was significantly (P < 0.05) higher for hot season samples (86.88%) than for cool season samples (85.59%). Expressed juice was significantly (P < 0.05) higher for cool season samples (36.84) than for hot season samples (35.74). Goat meat from the hot seasonal group was significantly (P < 0.05) darker than the cold season group based on L* (37.6 vs. 39.6), a* (20.0 vs. 23.3) and b* (3.6 vs. 4.2) colour measurements. These results indicated that high ambient temperatures had caused an increase in muscle ultimate pH leading to significant effects on meat quality.     

Consumer acceptance and appropriateness of meat substitutes in a meal context

The replacement of meat by meat substitutes could help to reduce the environmental burden of our food production systems. However, the acceptance of most meat substitutes is still low. This study investigated the role of meal context on the acceptance of meat substitutes. In a central location test involving 93 participants, meals with meat substitutes were rated on overall liking, product liking (liking of the meat substitute in the meal), appropriateness and intention-to-use, whereas individual meat substitutes were rated on overall liking. Meat substitutes with similar flavor and texture, but with different shape (pieces and mince), were rated differently in four meals (rice, spaghetti, soup, and salad) on product liking, appropriateness and intention-to-use, but not differently on overall liking of the meals. Meat substitutes with similar shape, but different flavor and texture rated differently on overall liking when tasted separately, but did not always differ in product liking when tasted in a rice meal. Appropriateness seemed to be influenced by the appearance of the meat substitute-meal combination, and less by flavor and texture. For the development of new foods (e.g. meat substitutes), more emphasis is needed on consumer evaluation of meal combinations instead of on the sensory properties of the individual product.     

Non-destructive assessment of instrumental and sensory tenderness of lamb meat using NIR hyperspectral imaging

The purpose of this study was to develop and test a hyperspectral imaging system (900–1700 nm) to predict instrumental and sensory tenderness of lamb meat. Warner–Bratzler shear force (WBSF) values and sensory scores by trained panellists were collected as the indicator of instrumental and sensory tenderness, respectively. Partial least squares regression models were developed for predicting instrumental and sensory tenderness with reasonable accuracy (R_cv = 0.84 for WBSF and 0.69 for sensory tenderness). Overall, the results confirmed that the spectral data could become an interesting screening tool to quickly categorise lamb steaks in good (i.e. tender) and bad (i.e. tough) based on WBSF values and sensory scores with overall accuracy of about 94.51% and 91%, respectively. Successive projections algorithm (SPA) was used to select the most important wavelengths for WBSF prediction. Additionally, textural features from Gray Level Co-occurrence Matrix (GLCM) were extracted to determine the correlation between textural features and WBSF values.     

Impact of carcass scalding and chilling on muscle proteins and meat quality of broiler breast fillets

The objective of this study was to determine the effects of broiler carcass scalding and chilling methods on meat quality and muscle proteins. During processing, carcasses were hard (60 °C, 1.5 min) or soft (52.8 °C, 3 min) scalded, and either immersion chilled (IC: 0.5 °C, 40 min) or air chilled (AC: 0.5 °C, 120 min). Breast fillets were deboned at 4 h postmortem and used for measuring meat quality and muscle protein characteristics. Scalding by chilling treatment interaction effects on meat quality were not observed. Air chilled carcasses had greater pH₂₄, and reduced drip loss and shear force compared to IC carcasses. Cook yield, color (L*a*b*), and moisture content were not different between chilling treatments. Scalding treatments did not influence quality traits. Sarcoplasmic protein solubility was not influenced by chilling treatment, but was greater in hard versus soft scalded carcasses. Myofibrillar protein solubility was greater in fillets from soft scalded IC carcasses. Alterations in the electrophoretic profiles of the myofibrillar and sarcoplasmic proteins due to treatments indicated minor changes in protein degradation and solubility. Data suggest that while only chilling method influenced meat quality, both scalding and chilling methods influenced protein solubility and degradation in breast fillets deboned 4 h postmortem.     

Evaluation of biochemical parameters and genetic markers for association with meat tenderness in South African feedlot cattle

A large proportion of South African feedlot cattle are crossbreds of Brahman (BrX, Bos indicus), and Simmental (SiX, Bos taurus). A sample of 20 grain fed bulls from each of these crossbreeds was used to compare meat quality with that of the small frame indigenous Nguni (NgX, Sanga) by evaluating a variety of biochemical and genetic parameters previously shown to be associated with meat tenderness. Shear force values were generally high (5.6 kg average at 14 days post mortem), with SiX animals higher than BrX or NgX (P = 0.051) despite higher calpastatin:calpain ratio in BrX (P < 0.05). Calpain activity and cold shortening were both correlated with tenderness for all classes. The sample size was too small to accurately estimate genotypic effects of previously published markers in the CAST and CAPN1 genes, but the allele frequencies suggest that only modest progress would be possible in these South African crossbreds using these markers.     

Water distribution and mobility in meat during the conversion of muscle to meat and ageing and the impacts on fresh meat quality attributes--a review

This paper reviews current knowledge on the distribution and mobility of water in muscle (myowater) ante- and post mortem and factors affecting these in relation to fresh meat quality parameters; water-holding capacity (WHC), tenderness and juiciness. NMR transverse relaxometry (T(2)) using bench-top Low-Field Nuclear Magnetic Resonance (LF-NMR) has characterised myowater distribution and mobility as well as structural features in meat which directly affect WHC. The current literature demonstrates that WHC is correlated to the water located outside the myofibrillar network (extra-myofibrillar). This review identifies the critical stages which affect the translocation of water into the extra-myofibrillar space and thus the potential for decreased WHC during proteolysis (the conversion of muscle to meat). This review discusses how the intrinsic properties of the water held within the meat could contribute to juiciness and tenderness. Tenderness has been shown to correlate to T(2), however breed and species differences made it difficult to draw firm conclusions. Further understanding of the inherent water properties of fresh meat and the factors affecting water distribution and mobility using NMR technologies will increase the understanding of WHC and tenderisation of fresh meat.     

Effect of modified atmosphere packaging on structural and physical changes in buffalo meat

The effect of modified atmosphere packaging of buffalo meat on the structural parameters viz., fibre diameter, sarcomere length and myofibrillar fragmentation index and physical parameters viz., pH, drip loss and colour scores were studied. The buffalo meat was packed under aerobic, vacuum and modified atmosphere (80% oxygen+20% carbon dioxide) and stored at 4±1°C upto 21 days. The results obtained revealed that vacuum-packed buffalo meat had the lowest fibre diameter and myofibrillar fragmentation index and the highest sarcomere length, vacuum thus appears to enhance ageing. Buffalo meat packed in modified atmosphere had a low drip loss and a desirable colour. The modified atmosphere packed and vacuum-packed buffalo meat was acceptable for upto 14 days at 4±1°C.     

宰后成熟过程中冷却牛肉、猪肉色泽和嫩度的变化

本实验比较研究了冷却牛肉和猪肉在宰后120h内色泽和剪切力的变化.分别从牛屠宰厂和猪屠宰厂选取牛、猪各4头,按规范工艺屠宰后取背最长肌,分切成8个肉块,经简易包装后在0～4℃下18、48、96、120h,之后测定肉色、剪切力值及其他相关指标.结果表明,牛肉和猪肉的pH值、肉色(L*、a*、b*)、水分含量、剪切力值等指标存在显著差异(p<0.05).随着成熟时间延长,亮度增加、红度下降、剪切力下降;宰后120h内,猪肉嫩度的变化比牛肉更明显.     

饲养方式对AA鸡屠宰后胸脯肌肉和腿肌肉僵直过程理化特性的影响

目的 研究笼养和散养方式对AA鸡宰后24 h内胸脯肌肉和腿肌肉理化特性的影响。方法 随机选择同一批相同饲养水平散养和笼养的AA鸡各30只。按照商业屠宰方法屠宰后, 鸡胴体冰水冷却1.5 h, 然后, 4 ℃冷藏至宰后24 h。宰后0、3、6和24 h时取样, 分别测定pH值、肌糖原含量、肌节长度、R-值和肌原纤维小片化指数(MFI)。结果 笼养鸡比散养鸡活体重高8.17 %, 且笼养鸡体重较均一。在宰后僵直过程中笼养鸡胸脯肌肉和腿肌肉pH值和肌糖原含量降低速度分别比散养鸡快。笼养鸡胸脯肌肉进入僵直比散养鸡胸脯肌肉早, 但是笼养鸡腿肌肉进入僵直时间比散养鸡腿肌肉晚。笼养和散养鸡不管是胸脯肌肉之间, 还是腿肌肉之间, 其肌节长度和MFI之间没有显著差异。并且宰后24 h, 本实验所测定指标在笼养和散养鸡之间不存在显著差异。结论 饲养方式(笼养和散养)除了对AA鸡活体重以外, 对屠宰后胸脯肌肉和腿肌肉的理化特性没有显著影响。     

Effect of low voltage electrical stimulation on biochemical and quality characteristics of Longissimus thoracis muscle from one-humped Camel (Camelus dromedaries)

The effects of electrical stimulation (90 V) 20 min post mortem on meat quality and muscle fibre types of four age group camels (1–3, 4–6, 7–9, 10–12 years) camels were assessed. Quality of the Longissimus thoracis at 1 and 7 days post mortem ageing was evaluated using shear force, pH, sarcomere length, myofibrillar fragmentation index, expressed juice, cooking loss and L^∗, a^∗, b^∗ colour values. Age of camel and electrical stimulation had a significant effect on meat quality of L. thoracis. Electrical stimulation resulted in a significantly (P < 0.05) more rapid pH fall in muscle during the first 24 h after slaughter. Muscles from electrically-stimulated carcasses had significantly (P < 0.05) lower pH values, longer sarcomeres, lower shear force value, higher expressed juice and myofibrillar fragmentation index than those from non-stimulated ones. Electrically-stimulated meat was significantly (P < 0.05) lighter in colour than non-stimulated based on L^∗ value. Muscles of 1–3 year camels had a significantly (P < 0.05) lower shear force value, and pH, but longer sarcomere, and higher myofibrillar fragmentation index, expressed juice, and lightness colour (L^∗) than those of the 10–12 years camels. The proportions of Type I, Type IIA and Type IIB were 25.0, 41.1 and 33.6%, respectively were found in camel meat. Muscle samples from 1–3 year camels had significantly (P < 0.05) higher Type I and lower Type IIB fibres compared to those from 10–12 year camel samples. These results indicated that age and ES had a significant effect on camel meat quality.     

Effect of salt,kinnow and pomegranate fruit by-product powders on color and oxidative stability of raw ground goat meat during refrigerated storage

Effects of salt, kinnow and pomegranate fruit by-product powders on color and oxidative stability of raw ground goat meat stored at 4 ± 1 °C was evaluated. Five treatments evaluated include: control (only meat), MS (meat + 2% salt), KRP (meat + 2% salt + 2% kinnow rind powder), PRP (meat + 2% salt + 2% pomegranate rind powder) and PSP (meat + 2% salt + 2% pomegranate seed powder). Addition of salt resulted in reduction of redness scores. Lightness increased in control and unchanged in others during storage. Redness scores declined and yellowness showed inconsistent changes during storage. Thiobarbituric acid reactive substances (TBARS) values were higher (P < 0.05) in MS followed by control and KRP samples compared to PRP and PSP samples throughout storage. The PSP treated samples showed lowest TBARS values than others. Percent reduction of TBARS values was highest in PSP (443%) followed by PRP (227%) and KRP (123%). Salt accelerated the TBARS formation and by-products of kinnow and pomegranate fruits counteracted this effect. The overall antioxidant effect was in the order of PSP > PRP > KRP > control > MS. Therefore, these powders have potential to be used as natural antioxidants to minimize the auto-oxidation and salt induced lipid oxidation in raw ground goat meat.