Consumer assessment of the effect of electrical stimulation on the colour and colour stability of Semimembranosus muscles

The influence of effective low voltage electrical stimulation on the colour stability of beef topside (semimembranosus) muscles, during storage and retail display was studied using objective measurements and subjective assessments. Earlier results obtained from objective measurements demonstrated that during a three day retail display period, stimulated topsides had a greater loss of colour than non-stimulated topsides, and primal cuts aged for 33 days at 0 °C before display suffered faster changes to colour during retail presentation than cuts aged for 5 days. To relate results obtained using objective methods to consumer perceptions of meat quality, consumer perceptions of samples of meat displayed for 3 days in the retail cabinets of a major local supermarket were recorded. A total of 960 consumers were asked to evaluate topside steaks for meat and fat colour, meat discolouration and acceptability. During 3 days of retail display, consumers did not perceive differences in the extent of discolouration of topside steaks from electrically stimulated and non-stimulated carcasses; for the majority of the treatment groups (high or low pH muscles, 5 or 33 day ageing, 1-3 day retail display) there were no significant differences, for any of the scored attributes, between stimulated and non-stimulated samples. However, for samples in the fresh (5 days ageing), high pH (5.8-6.0) treatments group, lean meat colour and acceptability for the stimulated samples were, on some of the days on display, given significantly (P < 0.05) better ratings by the consumers than those from corresponding non-stimulated samples.     

Storage and display characteristics of electrically stimulated, hot-boned and nonstimulated, cold-boned beef

One side, randomly selected from each of 33 carcasses from forage-fed steers, was electrically stimulated within 30 min of exsanguination and hot-bonded (ESHB). Opposite sides were not electrically stimulated and were cold-boned (NESCB) following a 24 h chill (0°C). From 17 ESHB sides, portions of the longissimus dorsi (LD) and semimembranosus (SM) muscles were removed and immediately vacuum packaged. LD and SM muscles were removed from the remaining 16 ESHB sides, wrapped in polyvinyl chloride film, chilled (0°C) for 22 h and then vacuum packaged. LD and SM muscles from NESCB sides (n = 33) were removed and the vacuum packed at 24 h post mortem. Whole muscle characteristics were evaluated initially and after storage periods of 7, 14 or 21 days and steaks were displayesd for 5 years thereafter. Neither hot versus cold-boning nor storage for 21 days affected retail display characteristics of LD and SM steaks (P > 0·05). As retail display time increased, retail lean color, fat color and overall appearance scores decreased.     

Effects of Beef Carcass Electrical Stimulation and Hot Boning on Display Color of Unfrozen Vacuum Packaged Steaks

Ninety-six beef sides from 48 carcasses were used to determine effects of control (C, chilled 48 hr at 5°C), electrical stimulation (ES, 45 min postmortem, 400 volts for 2 min, pulsed), and hot boning (HB, 2 hr postmortem), and combination (ESHB) treatments on muscle color of longissimus (LD) and semimembranosus (SM), vacuum packaged steaks. HB muscles frequently were visually brighter purplish-red than other treatments. Compared to ESHB, ES LD was not different, but ES SM was duller purplish-red in color. Reflectance indicators of reduced myoglobin and metmyoglobin were essentially the same across treatments in both muscles. Vacuum packaged fresh beef steaks from all treatments were acceptable in color at 0, 3, 7, and 14 days of display. Vacuum packaging appears suitable for steaks from any of these carcass treatments but is especially useful for steaks from hot boned cuts.     

Impact of RN genotype and ageing time on colour characteristics of the pork muscles longissimus dorsi and semimembranosus

The effect of RN genotype on pH decline, ultimate pH, pigment content, blooming and colour stability during 6 days of display at 5 °C was studied in two pig muscles, M. longissimus dorsi (LD) and M. semimembranosus (SM), and furthermore the effect of anaerobic storage time (2 days vs. 9 days of ageing) on the same parameters was examined. The postmortem pH decline was faster and the ultimate pH lower in LD and SM of the RN⁻ genotype compared with corresponding muscles from the rn⁺ genotype. Pork of the RN⁻ genotype was initially lighter and more red and yellow than pork of the rn⁺ genotype due to a higher degree of blooming, which might be explained by the faster pH decline and/or lower ultimate pH. The level of oxymyoglobin (MbO₂) was decisive for the redness of both muscles during display in air despite a higher presence of metmyoglobin (MetMb). Pork of the RN⁻ genotype was thus redder than that of the rn⁺ genotype throughout display in air despite higher oxidation to MetMb. Ageing for 9 days in chill improved the blooming potential in pork of both genotypes compared with 2 days of ageing, resulting in superior meat colour. However, only in pork from the RN⁻ genotype, the colour was not negatively affected by ageing time upon display in air.     

The significance of pre-slaughter stress and diet on colour and colour stability of pork

The influence of pre-slaughter stress and a diet known to affect post mortem muscle metabolism or a standard diet (control pigs) on colour and colour stability of m. longissimus dorsi, m. biceps femoris and m. semimembranosus from 112 female pigs, free of the Halothane gene, was investigated. Pre-slaughter stress increased the early post mortem temperature in the three muscles, as well as the pH decline in control pigs, but not in pigs fed the experimental diet. Colour was measured on sliced samples after 0, 2 and 5 days retail display (1, 3 and 6 days post mortem, respectively) from the three muscles aged 1 day before cutting as well as on sliced m. longissimus dorsi samples aged 8 days before cutting (8, 10 and 13 days post mortem, respectively). Early post mortem pH was not a main determinant of the colour and colour stability, while the degree of pre-slaughter stress and especially its influence on temperature early post mortem was crucial in relation to colour development and colour stability. The discoloration rate was enhanced in m. longissimus dorsi aged for 8 days prior to retail display compared with samples aged for 1 day. However, the extent of the discoloration after 5 days of retail display was not inferior in muscle samples aged for 8 days due to a higher degree of blooming. Finally, present data indicate that 3-4 days ageing of pork prior to retail display results in the optimal colour stability.     

Effects of Beef Carcass Electrical Stimulation and Hot Boning on Muscle Display Color of Polyvinylchloride Packaged Steaks

Ninety-six beef sides from 48 carcasses were used to determine the effects of control (C, chilled 48 hr at 5°C), electrical stimulation (ES, 45 min postmortem, 400 volts for 2 min, pulsed), hot boning (HB, 2 hr postmortem), and combination (ESHB) treatments on muscle color of longissimus (LD) and semimembranosus (SM) steaks packaged in polyvinylchloride film. LD from HB was mostly visually darker, had less oxymyoglobin, and more metmyoglobin than other treatments as was the SM, but SM had fewer differences between HB and ESHB. ES and ESHB muscles were visually similar, suggesting ES minimized the darkening effect of HB. Regardless of treatment, muscle color was acceptable at 0, 1, 3 and 5 days of display.     

Effect of dietary vitamin E supplementation on the colour and lipid stability of fresh, frozen and vacuum-packaged beef

The effects of dietary vitamin E supplementation on tissue α-tocopherol (α-Toc) levels and on the susceptibility of fresh, frozen and vacuum-packaged beef to lipid oxidation and colour deterioration were investigated. Friesian cattle were fed diets containing 20 (basal, n=5) or 2000 (supplemented, n=5) IU (α-tocopheryl acetate/kg feed/day for approximately 50 days prior to slaughter. α-Toc levels were higher (p<0.05) in muscles from supplemented animals than from those on a basal diet. Significant differences in α-Toc levels were also observed between muscles from different treatment groups, the order of the supplemented group was: M. psoas major (PM)>M. longissimus dorsi (LD)>M. gluteus medius (GM) (p<0.05), and in the basal group the order was: PM>GM>LD (p<0.05). Supplemented fresh, frozen and vacuum packed beef showed greater colour and lipid oxidative stability than meat from the basal group after 7 days retail display at 4°C (p<0.05). Thus, dietary (α-Toc supplementation appeared to retard metmyoglobin and TBARS formation in LD, GM and PM and increased the colour shelf life of these muscles.     

Metmyoglobin reducing activity and colour stability of ovine longissimus muscle

Characteristics of metmyoglobin reducing activity in ovine longissimus were determined, and its effect on colour and colour stability of muscle was investigated in two experiments. In the first experiment vacuum packed ovine longissimus samples were incubated at 5–35°C during the first 16 h post mortem (n=8 per treatment). Metmyoglobin reducing activity was negatively affected by incubation temperatures above 30°C, but colour and colour stability were little affected at 24 h post mortem and after 2 weeks of vacuum storage at 2°C. In the second experiment the effects of pre-slaughter stress and electrical stimulation on metmyoglobin reducing activity, colour and colour stability of ovine longissimus (n=40) with an ultimate pH below 5.8 were investigated. Neither of the treatments had an effect on metmyoglobin reducing activity or colour parameters. The relatively large variation in metmyoglobin activity and colour parameters allowed correlation analysis. Metmyoglobin reducing activity was not correlated to colour or the colour stability parameters. The results of the present study indicate that metmyoglobin reducing activity is not the primary determinant of colour or colour stability of ovine longissimus muscle.     

Aging and Processing Affect Color, Metmyoglobin Reductase and Oxygen Consumption of Beef Muscles

Color stability and various biochemical properties were determined in bovine longissimus dorsi and psoas major at different times postmortem (8 hr to 21 days) and during retail display. Surface metmyoglobin accumulation, metmyoglobin reductase activity and oxygen consumption rate were affected by muscle type, postmortem aging, and fabrication method (p < 0.01). Psoas steaks had greater metmyoglobin accumulation, lower metmyoglobin reductase activity, and greater oxygen consumption than longissimus steaks. However, color stability of muscles was similar after grinding, which increased oxygen consumption. Color was most stable in steaks fabricated at 4 or 7 days postmortem. The order of color stability was knife-cut steaks > saw-cut steaks > ground muscle.     

Electrical stimulation of pigs-effect on pH fall, meat quality and Cathepsin B+L activity

This work was performed to evaluate the effect of electrical stimulation (ES) on pH fall and meat quality of LD and BF in Danish halothane free pigs stunned with CO(2). ES resulted in a significant drop in pH of 0.3 units in both LD and BF and 3 h lairage resulted in 0.1 units lower pH at 20 min post mortem. Lairage time did not affect and did not interact with the effect of ES on any of the measured meat quality parameters. ES did not affect the ultimate pH in LD, BF, SM and SC or internal reflection value in LD. However, ES caused higher internal reflection and drip loss in BF and increased the PSE frequency in LD (2 to 7%) and in BF (2 to 49%). The frequency of PSE areas in the centre of SM was 70% for ES pigs compared to 9% for control pigs. ES and ageing improved the tenderness and reduced the hardness in LD as well as shear force of unaged BF. The effect of ES on tenderness and hardness was approximately half the effect of ageing, but the effect of ES and ageing were additive. ES significantly increased the activities of cathepsin B+L in the myofibrillar fraction, but there were no differences in proteolytic activity in the other fractions. It is concluded that ES improves tenderness in LD and BF, but has a negative effect on the quality of BF and SM. Therefore ES is not an economically attractive alternative for improvement of tenderness in LD compared to ageing in Danish pigs. ?     

Electrical stimulation of red deer (Cervus elaphus) carcasses - effects on rate of pH-decline, meat tenderness, colour stability and water-holding capacity

A total of 14 female red deer were included in a study on the effects of low voltage carcass electrical stimulation on meat tenderness, colour stability and water-holding capacity. Carcasses were randomly allocated to either electrical stimulation treatment (ES; 90-95 V unipolar pulses, 7.5 ms duration, 15 Hz for a duration of 55 s) or no electrical stimulation (non-ES) (n=7 in each group). Temperature and pH decline was recorded in M.m. triceps brachii, longissimus dorsi et lumborum (at the last rib; LD) and biceps femoris, at intervals from 0.5 to 20 h post-mortem. At 24 h post-mortem, LD from the left side were excised, vacuum packaged and refrigerated at -1.5°C. Glycogen concentrations, measured at 30 min post-mortem, and ultimate pH did not differ between groups. Compared to controls, ES increased the rate of muscle pH decline and produced lower shear forces at 1 day, 1 week and 3 weeks post-mortem, but these differences disappeared by 6 and 12 weeks post-mortem. Sarcomere lengths at 24 h post-mortem were unchanged by ES. After 1 week of refrigerated storage, ES significantly reduced display life (hours of Minolta a* value ? 12), but this difference disappeared at 3, 6 and 12 weeks of ageing. ES did not affect drip at any ageing time point. The present results demonstrate that the benefits of ES on tenderness are not permanent, and the procedure is not necessary for a long-term, chilled product. This study showed no detrimental effects of using electrical stimulation on meat colour stability or drip loss.     

The importance of chill rate when characterising colour change of lamb meat during retail display

An experiment was conducted to compare the effect of two chilling rates (Con and Fast) on colour change of lamb meat during simulated retail display. Measurements were made on 3 muscles; LD (m. longisimuss dorsi), SM (m semimembranosus) and ST (m. semitendinous). Meat samples from 32 Merino crossbred lambs were vacuum packed and stored for 5 days at 2 °C, then cut and overwrapped in polyvinyl chloride film on black polystyrene trays, stored in a display cabinet at 4 °C with lights on and measured twice daily for 4 days, using a Hunterlab minilab 45/20 L D65, aperture 10°. Sarcomere length was shorter, shear force higher and colour change greater in meat from the Fast treatment compared to the Con treatment. Colour differences between treatments were likely due to oxygenation (bloom) as well as oxidation effects. Chill rate is important when characterising colour change during display and should be considered in measurement protocols.     

Influence of packaging method and length of chilled storage on microflora, tenderness and colour stability of venison loins

Sections of venison loins (LD) weighing approximately 300 g from 12 red deer (Cervus elaphus) were packaged using four packaging methods: (a) vacuum packaging, (b) CO₂ flushed using a nylon containment film (CO₂-Nylon), (c) CO₂ flushed using an ultra-high barrier containment film (CO₂-UHB), and (d) CO₂ flushed using an aluminium foil laminate containment film (CO₂-Foil) and stored for 1, 6, 12 and 18 weeks at 0°C. Meat pH values were lower in all CO₂ flushed meat packages (P<0·05) than in vacuum packaged meat. Lactic acid bacteria and total anaerobic counts increased over storage time in all packages regardless of treatment up to values of log₁₀ 7·8 and 7·6 g⁻¹, respectively. Tenderness tended to increase as meat was stored for up to 18 weeks. Colour scores taken during simulated retail display indicated that colour deteriorated more rapidly when meat was stored for 12 and 18 weeks than for 1 and 6 weeks. Vacuum packaging and gas flushing (CO₂-Foil) resulted in higher initial colour scores than venison packaged in the CO₂-Nylon or CO₂-UHB materials. Venison stored for 18 weeks also exhibited a higher proportion of packages containing off odours, lower flavour desirability and flavour intensity scores as well as higher off flavour scores than meat stored for shorter times. The implications of these effects are discussed. Although there were few significant differences in microbial growth and sensory characteristics due to packaging method or containment film, vacuum packaging appeared to be the most economic and produced meat of better colour stability.     

Significance of storage time on degree of blooming and colour stability of pork loin from different crossbreeds

The objective was to investigate the effect of ageing time (1 day vs. 8 days postmortem) and sire breed used in the crossbreed (Duroc sired vs. Landrace sired pigs) on blooming ability and colour stability of pork M. longissimus dorsi (LD). The colour was measured during blooming (0, 10, 30, 60, 90 min and 24 h after cutting) and during subsequent display (1, 2, 3 and 6 days) at 3 °C. The contents of deoxymyoglobin (Mb), oxymyoglobin (MbO₂) and metmyoglobin (MetMb) were calculated. Ageing improved the blooming of LD from both crossbreeds with increased content of MbO₂ and decreased content of Mb, resulting in increased lightness, redness and yellowness. Ageing had smaller effect on colour stability with slightly lower MetMb in aged meat. Crossbreed affected both blooming and colour stability. LD from Landrace-sired pigs bloomed more than LD from Duroc-sired pigs, but more MetMb was formed during subsequent storage, although at a low level in both crossbreeds. The present data show superior colour characteristics of fresh pork aged for 8 days.     

Accelerated chilling and modified atmosphere packaging affect colour and colour stability of injection-enhanced beef round muscles

Beef knuckles were partially hot-boned within 1.5 h postmortem. Biceps femoris (BF), semimembranosus (SM), vastus lateralis (VL), and rectus femoris (RF) muscles were injection enhanced at 6% (experiment 1) or 10% (experiment 2) of non-injected weight and packaged in a high- (HiOx; 80% oxygen and 20% carbon dioxide) or ultra-low oxygen (LoOx; 80% nitrogen and 20% carbon dioxide) modified atmosphere. Hot boning accelerated chilling in all beef round muscles investigated. This resulted in a darker initial beef colour and darker visual colour during display for the BF, RF, and VL, as well as more uniform BF and knuckle steak colour. RF and VL, in experiments 1 and 2, respectively, had the most improved colour and colour stability. Steaks in HiOx MAP had longer colour life in display than steaks that had been in LoOx. Partially removing the beef knuckle early postmortem is a practical process that will improve colour and colour stability of beef round muscles.     

EFFECT OF ELECTRICAL STIMULATION AND BLADE TENDERIZATION ON PALATABILITY OF BEEF LONGISSIMUS AND SEMIMEMBRANOSUS MUSCLES

The effect of electrical stimulation (ES) and/or blade tenderization (BT) on palatability of longissimus (LD) and semimembranosus (SM) muscles from range-grazed and concentrate-fed steers were compared. Range-grazed steers graded lower and the steaks contained less fat and more moisture (P<0.05) than those from concentrate-fed steers. Broiled steaks from the range-grazed steers were less flavorful, less juicy, and less desirable overall than those from concentrate-fed steers (P<0.05). Nevertheless, tenderness of ES and BT treated steaks from range-grazed steers was comparable to steaks from concentrate-fed animals that had not been tenderized. Flavor and juiciness of LD muscle did not change with ES or BT treatments but flavor and juiciness of SM muscle decreased when combined ES and BT treatments were used.     

The effect of electrical stimulation on the quality of three bovine muscles

Meat bulls were randomly assigned to five treatment groups-intermittent electrical stimulation at 300 V (ES) at 5 min and 35 min post mortem (intact carcasses), 35 min post mortem (split carcasses) and non-stimulated controls (NS) (intact and split carcasses). Stimulated carcasses in all groups showed a significantly more rapid pH fall during the first 8h post mortem in adductor (AD), longissimus dorsi (LD) and triceps brachii (TB) muscles. Cooling rates were relatively slow. Samples were removed from the carcass at 24h post mortem. After vacuum storage at 3°C for 6 days stimulated muscles showed lower drip (LD and TB) and heating loss (TB), lower shear force values (AD, LD and TB) and higher taste panel scores (AD, LD and TB) compared with NS controls. No significant differences in tenderness were observed between the three ES groups. Sarcomere length assessment showed more contraction in NS carcasses, particularly in the superficially located LD and TB. These results suggest that cold shortening may occur in some muscles under cooling conditions so far considered safe in this respect. Since higher drip losses coincided with lower sarcomere lengths in these (NS) muscles, it is suggested that, under these conditions, ES may mask the increased drip losses which are possibly the result of muscle contraction. Furthermore, ES prevents the occurrence of cold shortening and, in addition, may exert some 'extra tenderising effect', which is not related to splitting of the carcass nor restricted merely to the LD muscle.     

Veal colour assessment with three wavelengths

A method to derive reflectance spectra and colour coordinates of meat by measurement of reflectance at only three wavelengths, 480, 570 and 620 nm has been developed, by treating the spectra of a meat sample as a linear combination of the spectra of the three major myoglobin derivatives (reduced myoglobin, oxymyoglobin and metmyoglobin). Applied to 300 samples of Semitendinosus and Longissimus dorsi veal muscles at different times post mortem (24 h to 9 d), colour differences ΔE (?) between the derived spectra and the real ones were about 1.5 units. The total pigment content, with high correlation with the extraction method (P < 0.02), and the relative proportions of the derivatives can also be estimated.     

Improving pork quality by electricalstimulation or pelvic suspension ofcarcasses

This investigation compared the separate and combined effects on meat quality of electrical stimulation (ES) and pelvic suspension of pig carcasses chilled rapidly or conventionally. Sides from 80 pigs, 80–90 kg live weight, were allocated to one of four treatments followed by either conventional chilling (1°C for 24 h) or rapid chilling (-20°C for 2–3 h, before 1°C until 24 h post-slaughter). The four treatments were: Achilles suspended, with and without high voltage ES, and pelvic suspended, with and without ES.

The quality attributes: pH, colour and opacity, drip loss, instrumental and sensory texture were measured in M. longissimus thoracis et lumborum, at 10 days post-slaughter. Rapid chilling reduced the evaporative weight loss by 0·5% There were no significant effects of treatment on colour or opacity, although ES samples were slightly paler. Drip loss was also slightly greater with ES, particularly when combined with pelvic suspension, but in no case was the meat classified as PSE. Instrumental measurements of 'texture showed improved tenderness from both ES and pelvic suspension, even after 10 days ageing. The improvement was less pronounced when ES and pelvic suspension were combined Taste panelling confirmed that samples treated by ES or pelvic suspension, separately or combined, were significantly more tender than samples from non-ES, Achilles hung sides. ES and pelvic suspension were equally effective in improving the tenderness of pork loin. Pelvic suspension did not suffer the disadvantage of increased drip loss that occurred with ES in this study.     

Colour stability of six beef muscles stored in a modified atmosphere mother pack system with oxygen scavengers

Summary The effect of O₂ scavengers on the colour stability of beef in retail overwrap trays within a modified atmosphere mother pack (CO₂/N₂) was assessed. Steaks from six muscles, namely Longissimus dorsi, Psoas major, Semimembranosus, Gluteus medius, Semitendinosus and Biceps femoris were examined. After storage for 2, 4 or 6 weeks mother packs were opened and steak colour was monitored during 96 h of retail display. Redness of all muscles stored with O₂ scavengers was superior to that of steaks stored without O₂ scavengers at all storage times. Hue angle results indicated some metmyoglobin formation in all muscles during storage. Comparisons were made between steaks stored with O₂ scavengers and fresh steaks. Shelf-life values were calculated using the reflectance difference method (R₆₃₀–R₅₈₀). O₂ scavengers did not affect weight loss from the stored steaks.