The relationship between early post-mortem pH and the tenderisation of beef muscles

The rate of early post-mortem pH fall in bovine muscle was studied to determine its influence on the rate and extent of the tenderisation process. The pH of M. longissimus dorsi (LD) and M. semimembranosus (SM) muscles of Hereford cross Friesian heifers (n = 127) was taken up to 24 h post mortem. Twenty-four LD and 24 SM muscles were selected according to their rate of pH fall; slow (n = 8), intermediate (n = 8) and fast (n = 8) and were sampled at 2, 7 and 14 days post mortem for sensory, mechanical, physicochemical and biochemical analysis. Fast glycolysing LD muscles were rated more tender in sensory analysis and texture assessment whereas slow glycolysing muscles were considered significantly tougher (p < 0.001). Fast glycolysing LD had a significantly lower shear force (p < 0.001) at each stage of ageing. Slow glycolysing LD and SM had the highest shear force values. No significant difference was found in intramuscular fat or moisture content between the groups. Slow glycolysing LD muscles had shorter sarcomere lengths at 2 days post mortem. SDS-PAGE electrophoresis patterns showed increased proteolysis, such as the earlier appearance of the 30 kDa fragment, which is believed to be a good indicator of tenderness, in fast glycolysing muscle. These results suggest that the rate of post-mortem pH fall plays an important role in proteolysis and tenderisation.     

Quantifying the extent of variation in the eating quality traits of the M. longissimus dorsi and M. semimembranosus of conventionally processed Irish beef

The aim of this investigation was to quantify the scale of variation in the eating quality of two commercial beef muscles, M. longissimus dorsi (LD) and M. semimembranosus (Sm). Both the LD and Sm were excised from steers (n=81) and heifers (n=81) (classification grade O4H, O4L, R4H, R4L) within 48 h postmortem, vacuum packaged and stored at 4?°C until tested for eating quality at 14 days postmortem. Quality measurements analysed were: pH, Warner Bratzler shear force, sensory attributes, sarcomere length, Hunter L a b muscle and subcutaneous fat colour and chemical composition. Extent of variation in many eating quality measurements, with the exception of most sensory attributes and subcutaneous fat colour, depended on gender, classification grade or a combination of both. The LD was more variable than the Sm for most quality attributes and heifers were more variable than steers. No one carcass grade was more variable over all attributes analysed; with different grades causing higher or lower variances within certain attributes. Knowledge of the current scale of variation in the eating quality of beef is required by the meat industry, and is one that requires further research.     

Effect of dietary vitamin E supplementation on cholesterol oxidation in vacuum packaged cooked beef steaks

The effect of dietary vitamin E supplementation on cholesterol oxidation in vacuum packaged, cooked, refrigerated and frozen beef steaks, was investigated. Steers (Friesian×Charolais×Black Hereford) were fed diets providing 20 or 3000 mg α-tocopheryl acetate/head/day for 135 days prior to slaughter. α-Tocopherol concentrations in M. psoas major (PM) and M. longissimus dorsi (LD) were significantly (p<0.05) increased by supplementation and were significantly (p<0.05) higher in PM than LD. Cholesterol oxidation (monitored by measuring 7-ketocholesterol formation) increased during refrigerated and frozen storage in some, but not all, groups, and tended to be higher in PM than LD. Dietary vitamin E did not affect 7-ketocholesterol formation in LD, but significantly (p<0.05) reduced concentrations in PM during refrigerated and frozen storage. Supplementation significantly (p<0.05) reduced TBARS in PM and LD, indicating that vitamin E improved oxidative stability in both muscles. The results show that dietary vitamin E supplementation inhibits cholesterol oxidation in vacuum packaged, cooked beef during refrigerated and frozen storage, but may be influenced by muscle type.     

Effect of high-oxygen atmosphere packaging on mechanical properties of single muscle fibres from bovine and porcine <Emphasis Type="Italic">longissimus dorsi</Emphasis>

The effect of storage in high-oxygen atmosphere packaging for 48 h at 4 °C on the myofibrillar component of meat toughness was studied performing tensile tests on single muscle fibres, isolated from beef and pork longissimus dorsi (LD). Storage of bovine LD for 48 h in the presence of oxygen significantly increased the breaking strength of single muscle fibres when compared with storage in a 100% nitrogen atmosphere. In contrast, the breaking strength of porcine LD stored for 2 days post-mortem in the presence of oxygen in the packages was not influenced.     

Textural Attributes of Mechanically and Cryogenically Frozen Whole Crayfish (Procambarus clarkii)

Textural quality of quick frozen and conventionally frozen whole crayfish was evaluated. Toughness, as measured by Kramer shear press, increased significantly (p≤ 0.05) as a result of freezing. Between 6 and 16 wk of frozen storage, toughness increased (p≤ 0.05) in seasoned (SCF) samples but remained the same in all other treatments. In all treatments, toughness declined after 16 wk of frozen storage. Individually quick frozen (IQF) samples were more tender (p≤ 0.05) than conventionally frozen (CF) samples. Seasoned crayfish had the greatest degree of toughness (p≤ 0.05). Extractable protein decreased (p≤ 0.05) during frozen storage, with IQF samples showing the smallest changes. SCF samples had significantly ( p ≤ 0.05) lower moisture retention and more (p≤ 0.05) lipid oxidation.     

Effect of electrical stimulation, hip suspension and ageing on quality of chilled pig meat

Carcasses from 60 Large white pigs, weighing 62-85 kg, were split and half were stimulated (700 V, 12·5 Hz for 90 s) 20 min after slaughter. Half of the stimulated (ES) and half of the non-stimulated sides were suspended from the Obturator foramen at 40 min after slaughter and resuspended from the Achilles tendon after 6 h. The sides were then subjected to one of two chilling treatments: (a) air at -15°C until M. longissimus dorsi (LD) in the lumbar region was below 10°C (approx. 3 h from slaughter), followed by air at 1°C for the remainder of chilling; (b) air at 1°C throughout. Rapid chilling increased toughness of LD but not M. semimembranosus (Sm). Stimulation improved tenderness in both muscles, increased drip loss in Sm and increased paleness in LD which could be reversed by rapid chilling. Pelvic suspension reduced drip and improved tenderness with similar magnitude to ES. Ageing improved tenderness in all except pelvic suspended sides but ES produced the most tender pork at 7 days.     

Identification of biomarkers of meat tenderisation and its use for early classification of Asturian beef into fast and late tenderising meat

BACKGROUND: The objective of this work was to study the post‐mortem evolution of potential biomarkers (µ‐calpain activity and proteolytic profile) of meat tenderisation in bovine longissimus dorsi (LD) muscle from several biotypes coming from two beef breeds (‘Asturiana de los Valles’ and ‘Asturiana de la Montaña’) and showing different levels of muscular hypertrophy (mh/mh, mh/+, + /+). RESULTS: LD samples were taken at 2, 12, 24 and 48 h and 3, 7, 14 and 21 days post‐mortem. The presence of muscular hypertrophy produced a faster rate of pH decline, faster exhaustion of µ‐calpain activity and earlier occurrence of proteolytic changes. Changes in the electrophoretic pattern of some peptides from sarcoplasmic (glyceraldehyde‐3‐phosphate dehydrogenase) and myofibrillar (troponin T and troponin I) muscle extracts within the first 24 h significantly correlated with meat toughness and allowed accurate discrimination of meat products into two groups: (1) fast tenderising meat, coming from mh‐biotypes, and (2) late tenderising meat, from normal (+/+) biotypes. CONCLUSION: Early monitoring (within 24 h after slaughter) of selected biomarkers in LD muscle allowed accurate prediction of ultimate meat toughness and could be used in the meat industry as a tool for early classification of beef into fast and late tenderising meat. Copyright © 2012 Society of Chemical Industry     

Effect of castration on bovine muscle composition

Samples of bovine muscles were cross-sectioned and stained for myofibrillar ATPase. Three fibre types were distinguished, I, IIA and IIB. In the longissimus dorsi (LD) muscles of steers the average occurrence of IIB fibres was 32%, but in bulls was only 8%. The difference was highly significant. In contrast, the average occurrence of I fibres in steers and bulls was not significantly different. IIB fibres were generally rare in splenius (Sp) muscle, and occurred in some steers but in no bulls. That IIB fibres were more common in steer muscle was confirmed by studies with pairs of identical twins. The increased occurrence of IIB fibres in steers was unrelated to carcass weight changes often associated with castration. Fibre type occurrence data in steer or bull muscles were highly variable. Also, muscles of twins remained macroscopically similar in spite of significant maleness differences between two animals of a pair. Together, these results indicate that castration exerted a relatively minor, but nonetheless significant, effect on the muscles studied. Other factors, such as breed, apparently exert greater effects: LD muscles of Sahiwal × Friesian bulls (a tropical-temperate cross) were very steer-like in composition. Areas of fibres increased with carcass weight. For LD, areas increased with similar slopes in steers and bulls, but for Sp, areas in bulls increased with steeper slopes. This difference related to the increased development of muscles about the neck in bulls. Further, in heavier bulls, areas of IIA fibres were significantly larger than areas of I fibres. Evidence is presented which suggests that the paucity of IIB fibres in bulls and the disproportionate area increases of IIA fibres in bull Sp, relate to the serum concentrations of androgens, which differ markedly in steers and bulls. Possible modes of action of androgens are discussed.     

Conjugated Linoleic Acid (CLA) content of meat from three muscles of Massese suckling lambs slaughtered at different weights

Eighteen Massese male lambs, fed mainly maternal milk were slaughtered at 11, 14 and 17kg. Samples of Longissimus Dorsi (LD), Triceps Brachii (TB) and Semimembranosus (Sm) muscles were collected. Milk from the lamb's dams was sampled weekly. Fatty acid composition of milk and meat was determined. TB was the fattest muscle, Sm the leanest one and LD showed an intermediate value of total lipids, while the weight at slaughter did not influence total intramuscular fat content in any muscle. Although slaughter weight slightly affected overall fatty acid composition of muscles, rumenic acid and total CLA content in TB and Sm, but not in LD, significantly increased with slaughter weight. As regard milk fatty acid composition, the contents of total CLA, RA and others minor CLA isomers decreased during the first four weeks after lambing and then increased at the last control (five weeks). The animals slaughtered at a live weight of 14 and 17kg showed a greater SCD enzyme activity (estimated by product/substrate ratio) and a higher rumen activity (estimated by means of branched chain and odd chain fatty acid content in meat) than animals slaughtered at 11kg. Cis-7, trans-9 CLA content significantly increased with the slaughter age in TB and SM, while trans-7, trans-9 CLA, only increased in TB, and cis-8, cis-10 CLA, only increased in SM. Further studies are needed in order to verify weather the different behaviour of RA in LD muscle may be due to differences in muscle metabolism or fatty acid utilisation.     

Sensory profiling of textural properties of meat from dairy cows exposed to a compensatory finishing strategy

A compensatory finishing strategy was evaluated to improve the quality of meat from dairy cows. The experiment included ten pairs of Holstein Friesian dairy cows. Each pair was the progeny of the same sire, in the same parity, and approximately at the same number of days in lactation before entering the experiment. Within each pair, one cow was allocated to a compensatory finishing strategy, dried off for 4 days, and further restricted in energy intake for another 17 days followed by 6 weeks of ad libitum feeding. The strategy improved the sensory texture and flavour of both M. longissimus dorsi (LD) and M. semimembranosus (SM). This was supported by lower shear force in both muscles (P < 0.02). The effect can be ascribed to various factors; in LD an increased amount of IMF plays a significant role, whereas in SM an increased protein turnover is suggested to be the dominating factor.     

Effects of blade tenderization on some quality characteristics of the muscles of mature ewes

 The effects of blade tenderization (BT) on some of the quality characteristics of longissimus dorsi (LD) and semimembranosus (SM) muscles from the carcasses of mature ewes were evaluated in this research. Values describing panel tenderness (P<0.01) and residue after chewing (P<0.05) were significantly improved by BT. Also, the number of chews before swallowing was significantly reduced (P<0.01) in the tenderized samples. The LD muscle had a significantly better (P>0.01) panel tenderness score and number of chews value than the SM muscle. BT influenced significantly (P<0.05) the initial yield force values of the Instron Warner-Bratzler test, which were 5.42±0.40 kg and 6.45±0.42 kg for tenderized and non-tenderized samples, respectively. Peak force and work done values were also significantly (P<0.01) affected by BT. The LD muscle had a lower peak force value (5.88±0.39 kg vs 7.06±0.43 kg) than the SM muscle. However, other Instron Warner-Bratzler test parameters were not significantly (P>0.05) affected by muscle type. The chewiness, hardness, peak force 2 and work done 2 values determined by the Instron compression test were significantly affected by muscle type. Also, BT resulted in lower values for chewiness, hardness, peak force 1 and 2, and work done 1 and 2 values, but the differences between tenderized and non-tenderized samples were not statistically significant (P>0.05). Received: 16 July 1998 / Revised version: 14 October 1998     

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.     

Further investigations into the relationship between ultimate pH and tenderness for beef samples from bulls and steers

Samples of longissimus dorsi muscle from 150 cattle comprising Friesian bulls and steers and Charolais × Angus cross steers, were used to investigate the nature of the relationship between ultimate pH and beef tenderness under conditions where cold-shortening was avoided. A modified Warner-Bratzler (WB) shear machine with a square- rather than a vee-blade enabled several aspects of tenderness to be evaluated, including peak force (PF), initial yield force (IY), PF-IY, and an index of total work done. The two steer groups differed little in meat quality characteristics, but, in terms of six major hindquarter cuts, the Charolais cross group yielded 14·3% more meat per unit live weight, due to a combination of a superior dressing-out percent and a higher cutability. Relative to Friesian steers, the bulls produced beef with a higher ultimate pH (P < 0·001), and after adjustment to a common pH, the bull beef was tougher for all WB parameters except PF-IY. Cooking loss was higher for beef from bulls after adjustment for pH. Although reduced by pH adjustment, beef from bulls remained significantly darker than that from steers (P < 0·05) based on reflectance measurements. Maximum toughness in terms of PF, IY, and work index was at an ultimate pH of 6·0-6·1, but the peak was much less clear for PF-IY. The decline in tenderness with an increase in ultimate pH to 6·2 was associated with a decrease in sarcomere length. This result supports a previous suggestion that shortening explains, at least in part, the lower average tenderness at intermediate pH values.     

Physiological Factors Influencing Toughness in Cooked Saddletail Snapper (Lutjanus malabaricus)

Saddletail snapper (Lutjanus malabaricus) is a commercially significant tropical species in Australia and has been the subject of consumer complaints of extreme toughness in cooked fillets. Textural and biochemical analyses including collagen and hydroxylysyl pyridinoline (PYD) cross‐links concentrations were conducted on 101 commercially harvested Saddletail snapper to identify causes of toughness. Fish age was found to account for 75.6% of observed variation in cooked muscle texture (work done) of Saddletail snapper. A significant linear relationship (P < 0.001) between PYD content and cooked muscle texture was also identified accounting for 50.3% of observed variation. The concentration ratio of PYD to total collagen (TC) ranged from 0.04 to 0.38 mol PYD per mol of TC. Fish size was also found to be a poor indicator of fish age and therefore a poor indicator of the potential risk of toughness of the cooked muscle.     

Feeding strategy for improving tenderness has opposite effects in two different muscles

Compensatory growth has been shown to affect rate of muscle protein turnover and may potentially improve tenderness of beef. Thus, a study of tenderness in relation to feeding regime and slaughtering at a time with maximal muscle protein degradation was performed. Friesian bull calves (5-month-old) were fed either ad libitum (n = 6) (AA) or restrictively for 3 months followed by re-alimentation for 6 weeks (n = 6) (RA) before slaughter at 10 months. At slaughter the fractional breakdown rate of muscle protein was 2.4% in RA compared with 1.6% in AA (P < 0.06). Sensory profiling revealed superior texture of M. semimembranosus from RA compared with AA, whereas M. longissimus was superior in texture from AA compared with RA, with no difference in proteolysis and shear force. In conclusion it was clear that different muscles in terms of tenderness responded very differently to the nutritional manipulation.     

Glutathione peroxidase activity,tissue and soluble selenium content in beef and pork in relation to meat ageing and pig RN phenotype

Since glutathione peroxidase (GSHPx) may be important for meat quality, its activity was examined in relation to animal species (beef and pork), muscle type (oxidative and glycolytic), selenium content, meat ageing and RN phenotype in Hampshire crossbred pigs. The GSHPx activity in bovine M. Longissimus dorsi [LD; 1.9 (0.4) U/g, mean (S.D.)] was significantly higher (P<0.001) than in M. Psoas major [PM; 1.5 (0.5) U/g] and the activities in the two muscles were correlated (r=0.66; P<0.001). Pork LD had a several fold lower GSHPx activity [0.4 (0.2) U/g] than bovine muscles but, in contrast, a somewhat higher content of selenium [113 (15) ng/g] than bovine LD [106 (12) ng/g] and PM [95 (17) ng/g]. The proportion of soluble selenium in bovine LD (72%) tended to be higher than that in bovine PM (64%), and it was significantly lower in pork LD (52%). Significant correlations between GSHPx activity and soluble selenium were obtained in both beef and pork. Thus, GSHPx activity varied among single animals, with species and muscle type, whereas meat ageing and pig RN phenotype had no effect.     

Comparison of functional and sensory attributes of high pH values in Semimembranosus and Longissimus dorsi of bull muscles during aging

Functional and sensory attributes were evaluated during aging for 96 h of high ultimate pH (pH > 6.2) Semimembranosus (Sm) from bulls. To investigate if type of muscle has an influence on these factors from dark, firm and dry (DFD) meat, the Sm muscle was compared with the Longissimus dorsi (Ld) muscle. Significant changes in pH and water holding capacity (WHC), dominant wavelength, lightness and viscosity were found between these muscles. The remaining functional and sensory properties between these muscles did not change signifi-cantly during storage. Bull's Sm muscle had lower pH (after 24, 48 and 72 h), WHC (after 24 and 48 h) and viscosity (after 24, 48, 72 and 96 h). However, the Sm muscles had higher cooking losses, less inten-sive flavour, less juiciness, tenderness and firmness.     

Quantifying changes in tenderness during storage of beef

An exponential decay equation was used to quantify changes in beef toughness during storage at constant temperatures between 0° and 20°C. Temperature had the greatest effect on tenderising rate—thirty-two times that due to animals and ten times that due to muscles which were M. longissimus dorsi, M. psoas major and M. semitendinosus. A common rate constant, derived at each temperature, showed that an increment in rate produced by a 5°C rise in storage temperature was then detectable and that the enthalpy of activation (ΔH¹) was 76 kJ/mole. Toughness constants differed most between muscles.     

Effect of delay time before chilling on toughness in pork with high or low initial pH

Paired M. longissimus dorsi muscles from 56 carcasses of Danish Landrace and Yorkshire breeds, slaughtered at approximately 90 kg live weight, were utilized to study the potential of cold induced toughness in pork. Based upon the pH value 45 min post stunning, the carcasses were divided in two groups: a low (5·7 ≤ pH < 6·1) and a high one (6·1 ≤ pH ≤ 6·5). The effects on Warner-Bratzler shear force, sarcomere length and myofibril fragmentation of inserting a delay time of 0, 2 and 4 h before carcasses entered the chilling tunnel (operating at -28°C to -22°C) were investigated on early excised muscles as well as on muscles removed 30 h post stunning. The left LD muscle from each carcass served as a control while all right sides were used for treatments. pH and temperature measurements obtained from LD muscles left on carcasses during chilling showed that LD muscles belonging to the high pH group involve a risk of cold shortening even when a 2 h delay was used before passing in to the chilling tunnel. Comparing pH groups, however, sarcomere lengths did not differ in control sides whereas the Warner-Bratzler shear force values were significantly higher in LD muscles taken from the high pH group. Early excision of the LD muscle resulted in shorter sarcomere lengths and increased WB shear force only for carcasses belonging to the high pH group, which, however, could be avoided by introducing a 4 h delay time before rapid chilling. The effect of delay time on tenderness from muscles excised from the carcass 30 h post stunning was much less but a 4 h delay did significantly (P < 0·05) improve tenderness in carcasses with high initial pH. Coefficient of correlation between Warner-Bratzler shear force and sarcomere length was -0·12 and nonsignificant in the low pH group, whereas it was -0·57 and highly significant in the high pH group.     

Chemical composition of two muscles of the common duiker (Sylvicapra grimmia)

Ten mature male common duikers (Sylvicapra grimmia) were cropped and their M longissimus dorsi (LD) and M biceps femoris (BF) dissected in order to determine the chemical composition of the meat of this species. There was no significant difference in proximate chemical composition between the LD and the BF. The duiker muscle had a moisture content of 713.1 g kg^?1, a high protein content (257.7 g kg^?1) and a low fat content (20.6 g kg^?1). Potassium and phosphorus were the minerals and lysine and leucine the amino acids present in highest concentrations in the meat. The LD contained higher levels of sodium and zinc than the BF but lower levels of alanine, leucine and lysine. Stearic acid, palmitoleic acid, oleic acid and linoleic acid constituted the greatest proportion of fatty acids in the meat. The common duiker's meat also had a high polyunsaturated fatty acid content (414.2 g kg^?1 total fatty acids), allowing it to be considered a healthy food commodity. Copyright © 2004 Society of Chemical Industry