High pre rigor temperature limits the ageing potential of beef that is not completely overcome by electrical stimulation and muscle restraining

Two simultaneous trials were conducted to determine the effects of electrical input [electrical stunning and stimulation (ES)], wrapping, pre rigor temperature (15 °C and 38 °C) and different post rigor chilling rates on beef quality using M. longissimus lumborum (n=100). The high pre rigor temperature induced a faster pH decline than ES. The loins at 38 °C had significantly greater protein denaturation, more purge and drip loss, higher shear force values and less desmin degradation compared with the loins at 15 °C. No difference in sarcomere length was determined between the pre rigor temperatures regardless of ES and wrapping. Different post rigor chilling rates did not play a substantial role in water-holding capacity, proteolysis, or shear force values during ageing. These results suggest that high pre rigor temperature induces temperature-related toughness of muscle due to protein denaturation with subsequent limitation of proteolysis by μ-calpain, regardless of ES and wrapping treatments.     

Effect of pre rigor stretching on beef tenderness development

The objective of this study was to determine effects of pre rigor stretching on beef tenderness development. Beef loins (M. longissimus dorsi; n = 24) were assigned to either stretching or non-stretching treatments and aged for 14 days at − 1.5 °C. Sarcomere length, shear force, water-holding capacity and proteolysis were determined for the loins at 1, 7 and 14 days of ageing. Stretching increased the length of the loins by 33% resulting in a trend of increasing sarcomere length (P = 0.19). However, no significant differences for shear force values, purge, drip and cooking losses between treatments were found. Shear force values decreased with ageing times (P < 0.05). Western blot assay found that stretching did not affect the extent of desmin degradation. The findings from the present study suggest that pre rigor stretching with the current increase in length will not contribute to tenderness improvement of the beef loins.     

Imaging optical diffuse reflectance in beef muscles for tenderness prediction

The objective of this study was to investigate the potential of a novel optical reflectance imaging method to predict beef tenderness. Two-dimensional (2D) optical reflectance in beef muscles induced by a point incident light was acquired. A set of five parameters were extracted from each reflectance image to describe quantitatively the reflectance profiles. Two parameters, q and B, were derived by numerically fitting the equi-intensity contours of the reflectance pattern. Two spatial gradients were calculated along the directions parallel and perpendicular to muscle fibers and total scattering intensity was obtained by excluding the specular reflectance. This method was applied to analyze 2D images of optical diffuse reflectance in 336 beef samples obtained from 14 steers in which large variations in tenderness were generated by altering animal genetics, suspension method and aging time as well as utilizing muscles varying in their inherent tenderness. Tenderness was evaluated using Warner–Bratzler shear force (WBSF). The effects of animal breed, muscle, types of suspension, and aging were investigated and results indicate that the scattering intensity measured at 1-d was correlated (R² = 0.50 at λ = 720 nm) with 10-d WBSF in M. longissimus dorsi muscles; and the q parameters measured at 1-d was correlated (R² = 0.46 at λ = 720 nm) with 10-d WBSF in M. psoas major muscles. These results show analyzing 2D reflectance images of meat surfaces provides valuable information regarding the physical characteristics of meat that are responsible for beef tenderness.     

Effect of muscle stretching on meat quality of biceps femoris from beef

The objective of this study was to examine the effect of muscle stretching on meat quality and ultrastructure of biceps femoris (BF) from beef. After slaughter, the right side of the carcasses were suspended from the Achilles tendon (AS; n=10), while the left sides were re-hanged from the pelvic bone (PS; n=10). Meat quality was evaluated by water holding capacity (WHC), cooking loss (CL), color, shear force (SF) and sarcomere length (SL). As a result, PS had no impact on WHC, CL and color parameters. PS significantly decreased SF values by 7.5% only at 2 days postmortem. At pelvic suspended sides, SL was increased by 0.13 μm, 0.14 μm and 0.12 μm at 2, 7 and 10 days postmortem, respectively (P<0.001). Electron microscopy showed that the ultrastructure of BF have longer sarcomeres and smaller fiber diameter after PS. In conclusion, PS is a useful method for improving tenderness by stretching muscles.     

The protective effect of electrical stimulation and wrapping on beef tenderness at high pre rigor temperatures

A three factorial experimental design involving electrical stimulation (ES/NES), wrapping (wrapped/unwrapped) and pre rigor temperature (15 °C or 35 °C) was applied to 70 beef M. longissimus lumborum muscles to obtain a wide variation in shear force and drip loss. The shear force of all treatment groups decreased during ageing. As anticipated, wrapping and electrical stimulation had positive effects on shear force. However, high pre rigor temperature (35 °C) did not result in higher shear force values if the muscles were electrically stimulated, wrapped or both. The results suggested that electrical stimulation protects against the negative effects of high pre rigor temperatures. The drip loss of all treatment groups increased during ageing in a manner that was unrelated to treatment but was correlated to tenderness (r² = 0.70; p < 0.0001). It was concluded that the application of electrical stimulation, whatever the pre rigor temperature, protects beef from toughening through the prevention of rigor shortening and the avoidance of inhibition of ageing enzymes.     

Tenderness of pre- and post rigor lamb longissimus muscle

Lamb longissimus muscle (n=6) sections were cooked at different times post mortem (prerigor, at rigor, 1dayp.m., and 7 days p.m.) using two cooking methods. Using a boiling waterbath, samples were either cooked to a core temperature of 70 °C or boiled for 3h. The latter method was meant to reflect the traditional cooking method employed in countries where preparation of prerigor meat is practiced. The time postmortem at which the meat was prepared had a large effect on the tenderness (shear force) of the meat (P<0.01). Cooking prerigor and at rigor meat to 70 °C resulted in higher shear force values than their post rigor counterparts at 1 and 7 days p.m. (9.4 and 9.6 vs. 7.2 and 3.7 kg, respectively). The differences in tenderness between the treatment groups could be largely explained by a difference in contraction status of the meat after cooking and the effect of ageing on tenderness. Cooking pre and at rigor meat resulted in severe muscle contraction as evidenced by the differences in sarcomere length of the cooked samples. Mean sarcomere lengths in the pre and at rigor samples ranged from 1.05 to 1.20 μm. The mean sarcomere length in the post rigor samples was 1.44 μm. Cooking for 3 h at 100 °C did improve the tenderness of pre and at rigor prepared meat as compared to cooking to 70 °C, but not to the extent that ageing did. It is concluded that additional intervention methods are needed to improve the tenderness of prerigor cooked meat.     

Evidence against the non-enzymatic calcium theory of tenderization

The objective of the present study was to determine whether variation in the tenderization of lamb longissimus could be attributed to variations in the rise in free calcium postmortem and sarcomere lengthening post rigor. The longissimus muscle of 10 crossbred lambs (Romney×Coopworth) was sampled at 1 and 7 days postmortem for determination of MIRINZ shear force, myofibrillar fragmentation index (MFI), sarcomere length, free calcium, and proteolysis of troponin-T. Despite considerable variation in tenderness and tenderization of the muscles, sarcomere lengthening was not observed. The concentration of free calcium at 7 days postmortem correlated significantly with the MFI (r=0.640; P<0.05) and tended to correlate with the shear force (r=−0.596; P<0.1) and degradation of troponin-T (r=0.625; P<0.1). Degradation of troponin-T was significantly correlated with tenderization (r=0.664; P<0.05). Troponin-T is a calpain substrate, but reportedly is not degraded through a direct effect from calcium. The present results, therefore, suggest that the variation in free calcium in postmortem muscle affects tenderization through an effect on the calpain system and not through a direct effect of calcium on myofibrillar proteins. Consequently, the results of this study do not support the (calcium) theory that calcium directly affects tenderization.     

Heat shock and structural proteins associated with meat tenderness in Nellore beef cattle,a Bos indicus breed

Nellore beef cattle, a Bos indicus (Zebu) breed, is well adapted to tropical conditions and has allowed Brazil to become one of the largest producers of red meat. Nevertheless, B. indicus breeds are reported to have less tender meat than Bos taurus. This study was designed to identify genes associated with meat tenderness and thus provides important information for breeding programs. A group of 138 animals was evaluated for longissimus thoracis muscle shear force (SF). Animals with the highest and lowest SF values (six animals each) were then selected for protein abundance studies. Samples were subjected to two-dimensional gel electrophoresis (2-DE) followed by peptide sequencing through mass spectrometry (MS) to identify differentially expressed proteins associated with SF values. Seventeen differentially expressed spots were observed (p < 0.05) between the two groups. The 13 proteins identified included structural proteins (alpha actin-1, MLC1, MLC3, MLC2F and tropomyosin), related to cell organization (HSPB1 and HSP70), metabolism (beta-LG, ACBD6 and Complex III subunit I) and some uncharacterized proteins. Results confirm the existence of differentially expressed proteins associated with SF, which can lead to a better understanding of mechanisms involved in meat tenderness.     

Pre rigor processing,ageing and freezing on tenderness and colour stability of lamb loins

Forty eight lamb carcasses with temperature and pH monitored were obtained from two commercial plants. At 24 h post mortem both loins (M. longissimus) from each carcass were randomly allocated to a) unaged frozen at − 18 °C, (b) aged at − 1.5 °C for 2 weeks before freezing, (c) aged for 3 weeks before freezing and (d) aged for 9 weeks without freezing. Shear force, colour stability and proteolysis were analyzed. Carcasses with a slower temperature and more rapid pH decline had more calpain autolysis, slightly higher shear force and less colour stable compared to that counterpart in general (P < 0.05). However, the shear force values of the loins were all acceptable (< 6 kgF) regardless of different pre rigor processing and ageing/freezing treatments. Furthermore, the loins aged for 2 weeks-then-frozen/thawed had a similar shear force to the loins aged only for 9 weeks suggesting that ageing-then-freezing would result in equivalent tenderness compared to aged only loins for the long-term storage.     

Effect of South African beef production systems on post-mortem muscle energy status and meat quality

Post-slaughter muscle energy metabolism meat colour of South African production systems were compared; steers (n = 182) of Nguni, Simmental Brahman crossbreds were reared on pasture until A-, AB-, or B-age, in feedlot until A–AB-age. After exsanguination carcasses were electrically stimulated (400 V for 15 s). M. longissimus dorsi muscle energy samples were taken at 1, 2, 4 and 20 h. Post-mortem samples for meat quality studies were taken at 1, 7 and 14 days post-mortem. Production systems affected muscle glycogen, glucose, glucose-6-P, lactic acid, ATP, creatine-P glycolytic potential (P < 0.05), with the muscles of feedlot carcasses having a faster glycolysis rate than pasture carcasses. Energy metabolites correlated (0.4 < r < 0.9) with meat colour (CIE, L*a*b*), (0.3 < r > 0.5) water holding capacity, drip loss, and Warner Bratzler shear force. Muscle energy only affected muscle contraction of the A-age-pasture system (shortest sarcomere length of 1.66 μm vs 1.75 μm highest WBS of 6 kg vs 5 kg 7 days post-mortem).     

Effect of dietary ractopamine on tenderness and postmortem protein degradation of pork muscle

Twenty-four finishing pigs with a mean starting weight of 82 kg were assigned to two dietary regimens: (1) a corn–soybean meal basal diet (control; n = 12), and (2) the basal diet supplemented with 20 ppm ractopamine HCl (RAC; n = 12). After 28–30 days on the feeding trial, pigs were slaughtered, and the growth and carcass characteristics were measured. Furthermore, the 3rd–13th rib section of longissimus muscle was excised at 48 h postmortem, sliced into 19-mm thick chops, vacuum packaged, stored at 2 °C, and subjected to Warner–Bratzler shear force (WBSF) and electrophoretic tests after 2, 4, 7, 10, 14, and 21 days (postmortem). RAC feeding increased (P < 0.01) pig carcass weight and percent lean, but it also increased the day-2 muscle WBSF by 20% (P < 0.01). The shear force difference between control and RAC pig muscles gradually decreased and vanished by day 10 (P > 0.05) when both muscle groups became more tender. The muscle from RAC-fed pigs exhibited a slower protein degradation rate than muscle from the control animals, notably for proteins in the 15–45 kDa range. The results suggested that the tenderness difference between ractopamine-treated and control pig muscles was related to the proteolysis rate, and could be diminished with adequate postmortem ageing.     

Effects of teeth maturity and fatness of Nellore (Bos indicus) steer carcasses on instrumental and sensory tenderness

This study sought to evaluate the effects of teeth maturity and carcass fatness on physical and sensory traits of the beef ribeye (M. longissimus thoracis). Carcass sides (n = 60) of Nellore steers were grouped into six categories, according to teeth maturity (2, 4 and 6 permanent incisors), and fatness (2 – slight and 3 – average). The boneless ribeye cuts (6th – 9th ribs) were vacuum packed and aged for 14 days. Steaks, 2.5 cm thick, were evaluated as to sarcomere length, shear force and sensory attributes. Sarcomere length was not affected (P > 0.05) by maturity or fatness. Teeth maturity did not influence (P > 0.05) tenderness measured by instrumental or sensory analysis, however rib steaks from fatter carcasses displayed better tenderness (P < 0.01) and lower cooking losses (P < 0.01). In the Nellore steer carcasses produced in Brazil, fatness may be more important than teeth maturity to improve meat tenderness.     

Limousin myostatin F94L variant affects semitendinosus tenderness

Texture parameters (peak force and compression), muscle myofibre diameter, and hydroxyproline were measured in semitendinosus samples from a cattle gene-mapping herd. The data were analysed to determine the relationships between these traits. The traits were also mapped by genetic linkage analysis to identify quantitative trait loci, and hence, candidate genes for these traits. Neither texture parameters were affected by the muscle structural traits of myofibre diameter or collagen content (as measured by hydroxyproline), despite significant variation in these traits between animals. QTL for the texture parameters of peak force and compression, as well as collagen content, were found on cattle chromosome 2 (BTA2) and attributed to the myostatin gene. Within the cattle population used for the QTL mapping, a gene variant of myostatin, F94L, has been previously shown to increase muscle mass, predominantly in the semitendinosus. It was determined herein that the F94L myostatin homozygous animals had more tender meat as measured by both peak force and compression. The variant was also responsible for a reduction in the collagen/elastin content of muscle. The myostatin F94L variant had no effect on muscle myofibre diameter of the semitendinosus, even though the variant causes substantial increases in muscle mass. Consequently, the increase in muscle mass of the variant must be due to myofibre hyperplasia and not hypertrophy. In addition, myostatin effects on tenderness are caused by changes in the extracellular matrix rather than muscle myofibre diameter.     

Effect of beef ultimate pH and large structural protein changes with aging on meat tenderness

This study investigated the effect of ultimate pH (pH_u) in beef on the degradation of large structural proteins during refrigerated storage using SDS-PAGE. M. longissimus dorsi from bull carcasses were selected and classified into three groups: low pH_u (≤ 5.79), intermediate pH_u (5.80–6.19) and high pH_u (≥ 6.2) muscles. Samples were then stored at − 1.5 °C for 1, 2, 7, 14, 21 and 28 days. Meat tenderness was measured at each aging time. Depending on meat pH_u, different protein patterns and degradation rates of structural proteins were found. Rapid changes of large structural proteins took place within 48 h post mortem. Besides titin and nebulin, degradation of filamin was clearly revealed. Two more large protein bands corresponding to myosin family members also exhibited fast decline with storage time. It suggested that the fast degradation of these proteins is a key factor in the improvement of meat tenderness.     

Tenderness enhancement of beef from Bos indicus and Bos taurus cattle following electrical stimulation

High voltage electrical stimulation (1130 V peak, 14.28 bidirectional half sinusoidal pulses/s) or low voltage stimulation (45 V peak, 36 alternating square wave pulses/s) was used on cattle: (1) low voltage stimulation applied for 10 or 40 s with fast and slow chilling or high voltage stimulation for 60 s with normal chilling, applied to 100% Bos taurus cattle, (2) low voltage stimulation (40 s) and high voltage stimulation (60 s) with normal chilling applied to mixed Bos indicus and B.taurus cattle, (3) high voltage stimulation (54 s) with normal chilling applied to B. taurus and B. indicus cattle of 0–100% B. indicus composition, and (4) high voltage stimulation (60 s) applied to 100% B. taurus and 100% B. indicus cattle. All stimulation parameters enhanced the tenderness of steaks from M. longissimus thoracis et lumborum (LTL) aged at 1 °C up to 28 days compared with non stimulated LTL. Short low voltage stimulation of 10 s was marginally more effective than no stimulation and longer durations of 40 s were very effective and high voltage stimulation was most effective.     

Near infrared spectroscopy as an on-line method to quantitatively determine glycogen and predict ultimate pH in pre rigor bovine M. longissimus dorsi

The potential of near infrared (NIR) spectroscopy as an on-line method to quantify glycogen and predict ultimate pH (pH_u) of pre rigor beef M. longissimus dorsi (LD) was assessed. NIR spectra (538 to 1677 nm) of pre rigor LD from steers, cows and bulls were collected early post mortem and measurements were made for pre rigor glycogen concentration and pH_u. Spectral and measured data were combined to develop models to quantify glycogen and predict the pH_u of pre rigor LD. NIR spectra and pre rigor predicted values obtained from quantitative models were shown to be poorly correlated against glycogen and pH_u (r² = 0.23 and 0.20, respectively). Qualitative models developed to categorise each muscle according to their pH_u were able to correctly categorise 42% of high pH_u samples. Optimum qualitative and quantitative models derived from NIR spectra found low correlation between predicted values and reference measurements.     

Effect of age and cut on tenderness of South African beef

The tenderness characteristics of 15 primal cuts of beef of three different age groups were assessed, and the most reliable cut to predict carcass tenderness was determined. Fifteen wholesale cuts from each age group, representing the full variation in fatness, were aged, cooked and underwent sensory evaluation, shear force resistance and proximate analysis. Collagen content and solubility was determined. Percentage fat was used as a covariant during statistical analyses. Tenderness, residue and collagen solubility of all cuts decreased significantly with animal age. Collagen solubility was the largest discriminant between the three age groups, while animal age had no significant effect on collagen content. Tenderness of primal cuts from the same carcass varied considerably, with collagen content and shear force resistance as the largest discriminants between the cuts. Cuts most representative of total carcass tenderness were M. vastus lateralis, M. semimembranosus, M. gluteobiceps, M. semitendinosus and M. triceps brachii caput longum.     

Influence of different cold storage temperatures during the Rigor mortis phase on fillet contraction and longer-term quality changes of Atlantic cod fillets

Pre rigor produced fillets of Atlantic cod become shorter and more firm than post rigor produced fillets. In pre rigor excised muscle from warm-blooded animals and warm-water adapted fish, cold shortening, extensive contraction during cold storage, is known to occur. The aim of the present work was to study if the extent of fillet shortening in Atlantic cod could be reduced by a slight temperature increase during rigor contraction. The results demonstrate that fillets from this cold-water species showed no cold shortening. On the contrary, the fillets contracted the least when stored at 0 °C during rigor contraction.     

Effect of three stored-grain fungi on the development of Typhaea stercorea

This study examined development times and ovipositional preference of hairy fungus beetles (Typhaea stercorea [L.] Col: Mycetophagidae), when reared on pure cultures of Aspergillus flavus Link, Eurotium rubrum König, Spieck and Bremer, and Penicillium purpurogenum Stoll., and the ability of hairy fungus beetles to develop in the presence of high levels of aflatoxin when fed A. flavus grown on coconut agar medium. Results indicate that hairy fungus beetles can complete their life cycle when fed these mold species grown on a defined medium in pure culture. Developmental times were shortest and females laid more eggs on pure cultures of A. flavus compared to E. rubrum, and P. purpurogenum. Lastly, we tested to see the effects of aflatoxin on hairy fungus beetle development. Hairy fungus beetles can complete their life cycle while feeding on a fungal culture producing high levels of aflatoxin. The results suggest that the mold species in the grain mass can influence insect developmental rates and thus population growth rates.