Influence of sonication on Warner-Bratzler shear force,colour and myoglobin of beef (<Emphasis Type="Italic">m. semimembranosus</Emphasis>)

Research in the past few decades has shown the potential benefits of using ultrasound treatment as a technique to enhance tenderness and sensory properties of meat and its sub-products. The objective of current study was to assess whether the low-frequency, low-intensity ultrasound treatment at 24 h postmortem affects the pH, Warner-Bratzler shear force (WBSF), colour (CIE L^*a^*b^*c^*H°), and relative proportions of myoglobin (Mb) redox forms and total Mb concentration during 96 h of beef (musculus semimembranosus) storage. Muscles were obtained from young bulls (n = 15) of Lowland Black and White breed slaughtered at a live weight of 475 (SD 16.1) kg. Ultrasound treatment did not have a statistically significant (p < 0.05) effect on the pH of meat directly after sonication (24 h postmortem), or at 72 and 96 h postmortem. Sonicated meat sample (S) was characterized by higher, but not statistically significant (p < 0.05), L* coordinate values 24, 48 and 72 h postmortem. During the whole storage period, colour coordinates a*b*c* and H° were not significantly (p < 0.05) affected by sonication. Ultrasound treatment accelerated the total colour change ΔE, limited the formation of MbO₂ and slowed down the formation of MetMb. Measurements carried out 48 and 72 h after slaughter revealed that the ultrasound treatment significantly (p < 0.05) reduced the WBSF. This study demonstrates the potential of low-frequency, low-intensity ultrasound treatment at 24 h postmortem for beef tenderization without detrimental effects on its CIE colour parameters and relative proportions of Mb redox forms.     

INFLUENCE OF ANTE-MORTEM GLYCOLYSIS AND DEPHOSPHORYLATlON OF HIGH ENERGY PHOSPHATES ON BEEF AGING AND TENDERNESS

The effects of ante-mortem glycolysis, and rapid post-mortem drop in pH and dephosphorylation of high energy phosphates on beef tenderness were studied using twelve major muscles from carcasses having post-slaughter pH values in the ranges 6.7–7.1 and 5.8–6.2. In muscles which had low post-slaughter pH, dephosphorylation of high energy phosphates and pH changes were complete in about 16 hr postmortem. On the other hand, these changes continued for up to 32 hr post-mortem in muscles which had high post-slaughter pH. Muscles with high post-slaughter pH values required about 7 days of aging to attain maximum tenderness, and were more tender than the corresponding low post-slaughter pH muscles aged for the same length of time or longer. Results suggest that the simple measurement of pH within 1 hr after slaughter may be useful for assessing the required aging time and the ultimate tenderness of beef.     

Calpain-calpastatin and toughness in M. longissimus from electrically stimulated lamb and beef carcasses

Shear strength, pH, temperature, μ-calpain, m-calpain and calpastatin levels were measured over a two-week post-slaughter period in Longissimus lumborum et thoracis (LD) from six lamb and six beef carcasses. All carcasses were subjected to high voltage electrical stimulation. The toughness of the beef LD determined by a MIRINZ tenderometer at 24 h post-slaughter showed a strong correlation (r=0.91) with pH of the LD at 3 h. Beef LD toughness at 14 days was correlated (r=0.84) with initial m-calpain levels. In both lamb and beef, LD toughness at 4 and 14 days respectively was also correlated with initial levels of calpastatin (r=0.85, 0.83, respectively). The strong correlation between calpastatin and the rate of tenderisation indicates that the calpain system is closely linked to the proteolytic breakdown of myofibrillar proteins. There is also evidence of an interaction between pH and μ-calpain activity. The μ-calpain, m-calpain, calpastatin, pH and temperature kinetic changes which occurred during the post-mortem ageing of beef and lamb LD were applied to a computer program which predicted rate of meat tenderisation by calculating in situ calpain activity. The closeness of fit between the predicted rate of meat tenderisation and the observed tenderness values of beef and lamb LD indicates that the post-mortem activity of μ-calpain is the major determinant of variations in tenderness. However, application of the meat tenderisation predictive program to LD from individual animals revealed that the program was not sufficiently robust for this use.     

Pre-slaughter stress arising from on-farm handling and its interactions with electrical stimulation on tenderness of lambs

The effect of electrical stimulation of lamb carcasses (n=269) or its absence (n=257) on shear force of m. longissimus thoracis et lumborum (LT) was monitored during ageing in pasture-fed merino lambs (n=526). The lambs were slaughtered on four different days allowing durations of between one to 10 days of recovery from pre-slaughter handling (yarding, weighing and crutching) that affected ultimate pH (pH(u)). The right LT was removed 20-40min post-slaughter, tightly-wrapped in cling film (prevents the muscle cross-section increasing and thus minimising shortening) and rapidly cooled to 15°C to enter rigor mortis and age. At 0, 4, 24 and 72h post-slaughter, pH measurements and samples for shear force measurement were taken. Pre-slaughter handling had a significant negative effect on pH(u) and several days recovery were required for pH(u) to reach values associated with optimal meat quality as reflected by pH(u). Lambs with one and three days recovery (no significant difference between them) had a pH(u)>5.7 in 50% of the muscles and 19.4%>pH(u) 5.8. Whereas, in lambs with 8-10 days recovery (no significant difference between them), only 8% had a pH(u)>5.7 and 3.1%>pH(u) 5.8. Within each slaughter day electrically stimulated lambs were always more tender than non-stimulated lambs. For non-stimulated muscles at 72h, shear force values >40N occurred for 11.2% of the muscles: for electrically stimulated muscles at 72h, shear force values >40N occurred for 1.9% of the muscles. The rates of tenderisation were slower for intermediate pH(u) values resulting in higher shear force values at all ageing durations. With ageing at 72h for intermediate pH(u), non-stimulated muscles (n=38) 17.64% were >40N and for stimulated muscles (n=34), 7.9% were >40N.     

Effect of low voltage electrical stimulation of pig carcasses and ageing on sensory attributes of fresh pork

The effect of electrically stimulating pig carcasses and ageing on sensory attributes of pork was evaluated in this study. A total of 48 female pigs [Duroc×Large White/Landrace (A; n=24) and Large White/Landrace (B; n=24)] were randomly allocated immediately prior to slaughter to one of two low voltage stimulation treatments; no stimulation or 150 mA applied for 30 s at 2 min post-exsanguination. Each side of the carcass was then randomly allocated to an ageing treatment of either 2 or 7 days post-slaughter. Muscle pH of the M. longissimus lumborum was lower (P<0.001) in electrically stimulated carcasses when measured from 40 min to 8 h post-slaughter compared with non-stimulated carcasses. Percentage drip loss, muscle lightness and PSE incidence were not influenced (P>0.05) by electrical stimulation. Electrical stimulation of pig carcasses and ageing pork for 7 days post-slaughter both improved (P<0.001) consumer scores for tenderness, juiciness, overall liking and quality category, however the interaction term of electrical stimulation and ageing was not significant for any of the sensory attributes. Pork from non-stimulated carcasses that was aged for 2 day post-slaughter was less tender (P<0.01) compared with pork in all other treatments. These results indicate that electrical stimulation (150 mA applied for 30 sec at 2 min post-exsanguination) was effective in improving eating quality attributes of pork, particularly when pork was aged for only 2 days post-slaughter, without detrimentally affecting colour or drip loss.     

A note on the discoloration of frozen porcine muscle,stored under fluorescent illumination,as influenced by an artificially induced high pH in the meat

The effect of an artificially induced high ultimate pH (pH_u, measured at 24 h post mortem), on metmyoglobin formation in frozen porcine muscles was investigated. The muscles were exposed to white fluorescent illumination whilst under storage at – 10°C. The results indicated that an artificially induced high pH was effective in retarding metmyoglobin formation in frozen muscles.     

Application of constant current, low voltage electrical stimulation systems to pig carcasses and its effects on pork quality

This study examined the effectiveness of a constant current, low voltage electrical stimulation system on improving pork quality when applied to pigs at 2 min post-exsanguination. A total of 48 female Duroc×Large White/Landrace pigs of 85–90 kg liveweight were randomly allocated immediately prior to slaughter to one of four constant current electrical stimulation treatments: control (no electrical stimulation), 50, 200 and 400 mA. Stimulation was applied to pig carcasses at 2 min post-exsanguination for 30 s. No differences (P>0.05) in WB shear force values, muscle lightness or PSE incidence of pork M. longissimus lumborum (LL) was found due to electrical stimulation treatment. Muscle pH of the LL muscle was lower (P<0.001) in carcasses in the 200 and 400 mA treatments compared to those from carcasses in both the 50 mA and control treatment groups, when measured at the various time points from 40 min to 8 h post-slaughter. Although carcasses stimulated with 200 and 400 mA had higher percentage drip loss (P<0.05) and purge (P<0.001), this was not found to impact WB shear force values, muscle lightness or PSE incidence.     

Variation in bull beef quality due to ultimate muscle pH is correlated to endopeptidase and small heat shock protein levels

This study set out to determine if ultimate pH (pH_u) affected the performance of intracellular small heat shock protein and endopeptidase dynamics in muscle during beef ageing. Longissimus dorsi muscles from 39 Angus or Limousin × Angus bulls were examined to see if pH_u achieved at 22 h post mortem (rigor) affected tenderness and water holding capacity of beef. Samples were segregated into three pH_u groups termed high (pH > 6.3), intermediate (5.7 < pH < 6.3) and low (pH < 5.7) pH_u beef. More than 30% of bull beef did not achieve acceptable tenderness at 8 days post mortem with this ageing regime. No significant differences in calpain or cathepsin enzyme levels due to meat pH were observed until after 22 h post mortem, but low pH_u beef had elevated caspase 3/7 activity soon after slaughter. At 22 h post mortem, greater levels of μ-calpain enzyme were found in the high and intermediate pH_u beef and cathepsin B levels were superior in the low pH_u beef after 2 days post mortem. Different rates of desmin and troponin T protein degradation were also observed in aged bull beef. Both proteins were degraded within 6 h post mortem for high pH_u beef, but took >3 days post mortem for intermediate pH_u beef. High levels of alpha β-crystallin (aβC) at 22 h post mortem coincided with delayed muscle protein degradation for low pH_u beef. Our results support the hypothesis that aβC shields myofibrils and buffers against endopeptidase degradation of beef structure during ageing.     

Relationship between rate of post mortem pH fall and ageing of Longissimus muscle in pietrain pigs

Twenty-six pietrain pigs exhibiting wide variability in pH₄₅ (pH value 45 min post mortem) values were used to assess the mechanical behaviour of cooked and raw Longissimus muscle at 24 h and 8 days post mortem. Rheological behaviour was studied in compression under strain conditions which allow specific determination of myofibrillar resistance. The muscles were divided into three groups on the basis of pH₄₅ values: (Severe pale, soft and exudative (PSE), pH₄₅ = 5.49 ± 0.03 (n = 9); PSE pH₄₅ = 5.78 ± 0.04 (n = 10); Normal, pH₄₅ = 6.35 ± 0.05 (n = 7). The three groups did not differ significantly for ultimate pH (pH_u = 5.57 ± 0.02 for the 26 muscles). A lower mechanical resistance of raw samples was found in the Normal group, regardless of the time post mortem. Although this difference was not significant, a significant relationship was found between this trait and pH₄₅ at both times post mortem (r = ?0.43, P < 0.05, at 24 h and r = ?0.44, P < 0.05, at 8 days post mortem). However, no significant effect of pH₄₅ was found on the mechanical resistance of cooked muscles. The relative decrease in myofibrillar strength after an 8-day ageing period was not affected by pH₄₅ but this was due to the fact that the three groups exhibited different starting points. Mechanical resistance of raw and cooked muscles at 24 h post mortem were significantly related to pH_u (r = ?0.55, P < 0.01, and r = ?0.49, P < 0.05, respectively). The present results show that after an 8-day ageing period, PSE muscles are not fully aged.     

Vacuum skin packaging and its effect on selected properties of beef and pork meat

Physicochemical, instrumental and microbiological examinations of steaks of beef and pork (m. longissimus lumborum) in vacuum skin packaging (VSP), conventional vacuum packing (CVP) and modified atmosphere packaging (MAP) were performed. Samples were stored at 2 ± 0.5 °C for 3 (pork) or 5 (beef) weeks. No statistically significant changes in pH values were recorded. Statistically significant (p < 0.001) changes in the thiobarbituric reactive substances content in modified atmosphere packed beef samples, and differences between samples in MAP and VSP or CVP were found from week 2 of the experiment onwards. The biggest changes in colour parameters were found in beef samples in MAP. The lowest and highest purge loss was recorded in samples in VSP and CVP, respectively. Vacuum packing enhanced the growth of lactic acid bacteria (LAB). At the end of the experiment, their numbers ranged from 4.31 log₁₀ cfu g^?1 (pork in CVP) to 5.14 log₁₀ cfu g^?1 (beef in VSP). LAB populations reached 2 log₁₀ cfu g^?1 in MAP beef and pork samples. On the other hand, MAP enabled the development of bacteria of the genus Pseudomonas and Brochothrix thermosphacta. The highest increase in coliform bacteria counts was recorded in vacuum-packed pork.     

Influence of ultimate pH on biochemistry and quality of Longissimus lumborum steaks from Nellore bulls during ageing

Ultimate pH (pH_u) is an indicator that influences post-mortem meat quality. We studied physiological and biochemical changes of steaks obtained from Nellore bulls (Bos indicus) during post-mortem ageing. To this, Longissimus lumborum (LL) muscles were classified into three groups: Normal-pH_u (≤5.79), Intermediate-pH_u (5.80–6.29) and High-pH_u (≥6.30) groups, portioned into steaks, vacuum packaged and matured at 2 °C for 0, 7, 14, 21 and 28 days. High-pH_u steaks exhibited impaired colour stability and were darker compared to the other groups. High- and Normal-pH_u steaks showed improved tenderness and myofibrillar fragmentation linked to proteolysis. Intermediate-pH_u steaks were associated with a lower meat tenderness and decreased collagen solubility. High-pH_u steaks retained a high pH during ageing and increased water-holding capacity. These findings provide evidence that highlight pH_u as a strategy for the classification of pH_u-dependent beef quality from Nellore bulls that can be adopted by the Brazilian meat industry.     

Rapid chilling has no detrimental effect on the tenderness of low-voltage electrically stimulated M. longissimus in Chinese bulls

This study investigated the effect of pre-rigor rapid chilling (RC) on the rate of pH and temperature decline, shear force values and ultrastructure of M. longissimus from beef carcasses exposed to electrical stimulation (ES). Chinese bull carcasses were electrically stimulated, and the alternate sides of the carcasses either were chilled conventionally (CC, 0-4°C, air speed 0.5 m/s for 24 h) or they underwent RC (-14±1°C, air speed 3 m/s for 2 h and then cooled under CC conditions until 24 h post-mortem). The results showed that RC increased the rate of temperature decline (P<0.05) and decreased the rate of pH decline (P<0.05). There were no significant differences in the shear force value and sarcomere length of M. longissimus between the two treatments (P>0.05). The results of this study indicate that RC has no detrimental impact on the tenderness of beef carcasses exposed to ES.     

Fasting-induced glycogen depletion in different fibre types of red and white pig muscles—relationship with ultimate pH

The aim of the present work was to study the effect of fasting times (0, 24, 48 and 72 h) on glycogen level in different fibre types of a predominantly white (Longissimus, LD) and a predominantly red (Semispinalis, SS) pig muscle, and on ultimate pH (pH_u, 24 h post mortem). Thirty two individually housed Large White castrates (eight pigs per treatment) were slaughtered individually under minimal stressful conditions. Muscle samples were taken during bleeding for enzymic determination of muscle metabolites and histological examination using computerised image analysis. Myofibres were classified by a combination of metabolic (W, white; R, red) and contractile (α, fast-twitch; β, slow-twitch) characteristics. The SS showed higher glycogen depletion after 24 h fasting than the LD (?55 versus ?26%, respectively). No further significant changes in glycogen level were recorded with enhanced fasting times (up to 72 h), although in the SS a marked trend towards glycogen depletion was observed. Fasting for 24 h resulted in significantly increased pH_u in the SS whereas for the LD, a significant increase in pH_u occurred only after 48 h fasting. In response to fasting, significant decrease in histochemical staining intensity for glycogen occurred in the three fibre types of the SS. The βR fibres of the SS showed an almost complete glycogen depletion after 24 h fasting. With increasing fasting time, glycogen was further depleted in fast-twitch fibres (αW and αR). In the LD, only fast-twitch fibres exhibited significant decrease in glycogen level after 24 h fasting. However, this was of a much lower magnitude than that observed in the SS and furthermore, no further variation was recorded with increasing fasting time, regardless of fibre type. The present work is the first to report a significant interaction between muscle type and fasting-induced glycogen depletion in pig. Furthermore, these results demonstrate that within each muscle, the extent of fasting-induced glycogen depletion is strongly fibre-type-dependent.     

Electrical stimulation and ageing of carcasses from red,fallow and New Zealand wapiti-type male deer

Farmed male red deer (15 and 26 months), fallow deer (16 months) and New Zealand wapiti-type deer (26 months) slaughtered in an experimental abattoir were used to determine the influence of processing practices on tenderness and pH. Carcasses were electrically stimulated (low voltage) through the leg or anus immediately after bleeding and compared with non-stimulated carcasses. Portions of loin and leg from all carcasses were subjected to a range of conditioning and ageing treatments before tenderness assessment was done with a Warner-Bratzler shear press. Tenderness was measured in some samples after a freeze and slow thaw cycle. Electrical stimulation in all deer types had a highly significant effect in improving tenderness and the effects were most dramatic when carcasses were placed in a chiller 2 h after slaughter. Conditioning and ageing regimes (maximum 96 h post-slaughter) further improved tenderness, particularly in non-stimulated carcasses. Processing effects were more marked in loin pieces; these cooled more rapidly than leg. The process of freezing and slow thawing (20 h at 4°C in loins and 24–96 h at 0°C for legs) improved tenderness by 10–40% when compared with unfrozen pieces. There were highly significant reductions in the pH values of legs due to stimulation as measured during the early stages after slaughter. A decline in pH with time post-slaughter was also evident. The results were consistent with the post-slaughter pH profile of loins. Electrical stimulation, via either the leg or the anus, gave similar results. An exception was the loin pH measurement from anally stimulated wapiti stags which appeared higher than their leg-stimulated counterparts. Where data were collected from both sides of leg-stimulated carcasses, pH values were around 0.13 units lower for the stimulated shackled leg than for the free leg. Leg temperatures rose to over 40°C at 0.5 h post-slaughter in all deer. Temperatures were generally similar between stimulated and non-stimulated carcasses for both loin and leg data.     

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.     

The effect of high and low voltage electrical stimulation on beef quality

Meat bulls were assigned to three treatment groups—high voltage intermittent electrical stimulation, low voltage electrical stimulation and no stimulation.Both stimulation methods resulted in a significantly more rapid pH fall in the longissimus and adductor muscles during the first 8 h post mortem. Carcass cooling rates were relatively slow, since temperatures of the longissimus and adductor muscles were 15°C, respectively, at 8 h post mortem.Samples of stimulated longissimus, cut at 24h post mortem and vacuum stored at 3°C for 6 days, had a brighter red colour, higher drip and heating loss, lower shear force values and scored better in taste panels, compared with samples from control carcasses. No significant differences were observed between high and low voltage electrical stimulation in quality traits measured.Although the combined result of pH and temperature measurements during the first 8 h post mortem suggest an absence of cold shortening conditions in control carcasses, a lower sarcomere length was found in samples of the longissimus muscle taken from these carcasses at 24 h post mortem.     

Effect of electrical stimulation,delayed chilling and post‐mortem aging on the quality of M. longissimus dorsi and M. biceps femoris of grass‐fed steers

BACKGROUND: Roughage‐based low‐input beef production systems are gaining increasing interest owing to the perceived ecological advantages and potential health benefits associated with the favourable fatty acid composition of such beef. The low plane of nutrition may on the other hand yield less tender beef by affecting growth, carcass weight and fatness and therefore, indirectly, early post‐mortem (p.m.) proteolytic enzyme activity and sarcomere shortening. This study aimed to examine delayed chilling and electrical stimulation as promising techniques to control early p.m. muscle metabolism in a way that improves the tenderness of beef from purely grass‐fed steers in comparison with that from steers receiving a finishing diet with concentrates. RESULTS: Electrical stimulation decreased the pH at 1.5 and 3 h p.m. in the M. longissimus dorsi (LD) and M. biceps femoris (BF) of the treated carcass sides as well as the maximum shear force in the LD, while delayed chilling had no effect on pH or texture. The interactions of carcass fatness with electrical stimulation (P = 0.025) and delayed chilling (P = 0.089) indicated more pronounced effects of the p.m. treatments on beef texture in leaner carcasses. CONCLUSION : Electrical stimulation, but not delayed chilling, could markedly improve pasture beef texture and reduce the aging period needed for proper tenderisation. Copyright © 2008 Society of Chemical Industry     

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