Effect of Different Photoperiods on Quality Attributes and Oxidative Stability of Breast Meat (M. Pectoralis Major) from Broilers

ObjectivesIn the broiler industry, high photoperiod (the duration of light exposure per day) regimes have traditionally been utilized to increase yield of breast meat, as well as maximize feed intake and growth rate in the growing period. However, recent literature reports this practice may have adverse effects on broiler welfare, resulting in impaired mobility and increased incidence of leg abnormalities. However, little information available in the current literature regarding effects of photoperiod on meat quality attributes and oxidative stability of broiler meat. Thus, the objective of this study was to evaluate the quality characteristics and lipid/protein oxidative stability of breast meat from broilers that were exposed to different photoperiod combinations.Materials and MethodsA total of 432 Ross 308 broiler chicks were allocated among 4 rooms each subjected to one of the following photoperiod treatments (hours Light: Dark): 20L:4D, 18L:6D, 16L:8D and 12L:12D, with 6 pens per treatment. At d 42, 2 broilers per pen (12 broilers/treatment) were randomly selected, harvested and air chilled for 24 h at 2°C. At l day postmortem, paired breast muscles (M. pectoralis) were collected for the meat quality analyses such as, water-holding capacity (drip/purge/cook loss), Warner-Bratzler shear force (WBSF), and display color for 7 d under fluorescent light (1450 lx). Lipid oxidation was assessed via the TBARS assay and protein oxidation by thiol content measured at d 1 and d 7 of display. The experimental design was randomized complete block design. Data were analyzed using the PROC MIXED procedure of SAS, and means were separated using least significant differences (P < 0.05).ResultsPhotoperiod had no effect on fillet yield and pH (P > 0.05). No significant difference in WBSF was found between treatments, although 12L:12D had a trend of higher WBSF (P = 0.08). Higher moisture loss during carcass chilling was found in carcasses from 20L:4D compared to 16L:8D and 12L:12D treatments (P < 0.05). No other measure of water-holding capacity was affected, though the 16L:8D treatment demonstrated a trend of higher freezing/thawing loss compared to other treatments (P = 0.06). Proximate moisture, protein and lipid contents were unaffected by photoperiod (P > 0.05), but higher ash was observed in 16L:8D over 20L:4D and 18L:6D (P < 0.05). Different photoperiod combinations affected color stability of breast meat during display (P < 0.05). Of note, fillets from 20L:4D maintained highest L* and hue angle, and least a* values (P < 0.05), indicating inferior color stability compared to other treatments. Oxidation increased with display, and fillets from 20L:4D and 18L:6D had higher TBARS over 12L:12D (P < 0.05); no photoperiod effect was observed in thiol content (P > 0.05).ConclusionResults suggest 20L:4D photoperiod regimes may be detrimental to meat quality, as carcasses from this treatment group had higher moisture loss during chilling, and color measurements characterized these fillets as being paler and more discolored than other treatments. Fillets from 12L:12D maintained lower TBARS than 20L:4D and 18L:6D, suggesting photoperiod regimes allowing more hours of dark may be beneficial in improving oxidative stability. Further studies determining the effects of photoperiod on quality and protein functionality of chicken meat for processing technological would be highly warranted.

Functional/Physicochemical Properties and Oxidative Stability of Ground Meat from Broilers Exposed to Different Photoperiods

ObjectivesProlonged photoperiod (light) is a common practice in the broiler industry to maximize feed intake, growth and yield. Several studies, however, have found negative impacts of extended photoperiod on animal welfare-related characteristics (e.g., leg abnormalities). While the previous research has primarily focused on animal growth/welfare aspects, the effect of photoperiod on functional properties and quality attributes of broiler meat has not been evaluated. Thus, this study was aimed to determine functional properties, physicochemical attributes and oxidative stability of ground meat from broilers reared under different photoperiod conditions.Materials and MethodsRoss 308 broiler chicks (n = 432) were assigned to 4 rooms with 6 pens per treatment, which were equipped with one of the following photoperiods (T20, T18, T16, and T12; the hours of lighting per day), started from Day 15. At 42 d of age, the broilers (n = 12/treatment) were randomly taken, slaughtered and chilled for 24 h at 2°C. At 1 d postmortem, tenderloins and leg muscles were separated from the carcasses and stored at –40°C until further processing. In three batches, meat samples were ground using 1/4 in plate and formed into patties (100 g each). The ground samples were measured for pH, protein solubility, emulsion activity index, protein denaturation, salt-induced water uptake and subsequent cooking loss and final yield. The patties were displayed at 2°C under light (l × 1800) and color stability, lipid oxidation (TBARS) and thiol contents were examined. The patties were also measured for purge/cooking loss and texture profile analysis (TPA). All data were analyzed using the PROC MIXED procedure of SAS (v.9.4). Means were separated using least significant differences (P < 0.05).ResultsT20 samples had the lowest sarcoplasmic protein solubility among treatments, while T18 had a lower myofibrillar protein solubility compared to other treatments (P < 0.05). The emulsion activity index of T20 was higher in sarcoplasmic fraction than T12 (P < 0.05). T20 group also had a lower extractable protein concentration compared to other treatments, which subsequently resulted in an increase in protein denaturation (P < 0.05). T20 samples had a lower value of pH, salt-induced water uptake, and cooking loss, while T18 had a lower final yield than T16 and T12 (P < 0.05). No differences in physicochemical traits of patties were found between treatments, indicated by TPA, purge and cooking loss results (P > 0.05), however T20 had a greater display weight loss than T12 (P < 0.05). T20 patties maintained the highest L* and hue angle values during entire display, which could be attributed to its inferior water-holding capacity (P < 0.05). Both lipid (TBARS) and protein oxidation (thiol content) were increased with display (P < 0.05), but no significant photoperiod effect was found (P > 0.05).ConclusionThe results from the present study indicate that extended photoperiod would result in adverse impacts on functional/technological properties and oxidative stability of broiler meat. This is the first study reporting the importance of broiler housing condition (photoperiod) and its subsequent impacts on final meat quality and processing properties. The findings would provide insights into development of mitigating strategies for the poultry industry to prevent quality deteriorations of broiler meat due to the extended photoperiod.

Impacts of Various Dry-Aging Methods on Meat Quality and Palatability Attributes of Beef Loins from Cull Cow

ObjectivesBeef from cull cows has been traditionally perceived as low-quality/value meat due to its inferior flavor and tenderness. Given the negative consumer perception of highly processed fresh meat, there is a need to develop a natural post-harvest aging system to improve eating quality attributes of beef products, particularly from cull cows. Dry aging has been practiced for decades as a traditional and natural butchery process, which is also known to improve palatability characteristics. Thus, the main objective of this study was to evaluate the impact of different dry-aging methods on meat quality, microbiological properties and palatability attributes of loins from cull cow beef.Materials and MethodsPaired beef loins from 13 carcasses (Holstein, 30+ mo) were obtained at 5d postmortem, divided into 4 equal length sections and randomly assigned to four aging methods: wet-aging (WA), dry-aging (DA), dry-aging in water permeable bag (DWA) and UV-light dry-aging (UDA; 2 treatment/day, 5 J/s/treatment). Sections were aged for 28d at 2°C, 65% RH and 0.8 m/s air flow. After aging, dry-aged sections (DA, DWA and UDA) were trimmed of dehydrated surface, and trim loss and total saleable yield were recorded. The pH, proximate composition, shear force, water-holding capacity, initial color (instrumental and trained panelist), lipid oxidation (2-thiobabituric acid reactive substances, TBARS), microbial properties (aerobic plate count (APC), lactic acid bacteria (LAB), and yeast and mold (YM) counts) and trained sensory evaluation (11 panelists) were determined. Experimental design was a balanced complete block design. All data were analyzed using PROC MIXED procedure of SAS, and least squares means for all traits were separated (P < 0.05).ResultsDA and UDA had a substantial moisture loss during the aging process, accompanied with higher trim loss compared to other methods (P < 0.05). This resulted in DA having the lowest yield followed by UDA, DWA and WA with the highest saleable yield (P < 0.05). No significant differences were observed on cook loss, WBSF and TBARS between the treatments. DWA had the lowest pH out of all treatments (P < 0.05). UDA had the lowest moisture content and highest drip loss (P < 0.05). Color measurement showed that both DA and WA had significantly higher L* and lower b* values compared to UDA and DWA (P < 0.05). However, a* and lean surface color were not significantly different between the treatments (P > 0.05). For the trim, UDA had the lowest microbial growth among all treatments (P < 0.05). For the lean, UDA had the lowest count for LAB (P < 0.05), WA had the lowest in YM (P < 0.05) and no difference was found for APC between treatments (P > 0.05). Trained sensory panelist found that UDA and WA had higher fat and sour flavor (P < 0.05), and a trend (P = 0.07) of higher oxidized flavor when compared to DWA and DA.ConclusionThe results showed that dry-aging would result in no adverse impact on shear force, cooking loss, initial color and lipid oxidation of mature beef loins. Further, sour and oxidized flavor was lower in dry-aged beef, indicating its potential as value adding process. UV light application minimized microbial growth during dry-aging process, although more analyses are needed to understand its full impact on dry-aged meat quality. Further studies on determining the consumer acceptability as well as flavor-related compound analyses are currently under investigation.

Apoptotic and Proteolytic Attributes and Metabolomic Changes in Postmortem Muscles from Pigs Subjected to Post-Weaning Transport at Different Seasons

ObjectivesPost-weaning transport of pigs was commonly practiced in the swine industry, however, adversely impact animal growth and well-being due to concurrent stress from weaning and transport. Further, our recent study found that post-weaning transport may have long-term effects on final pork quality attributes in terms of inferior texture and water-holding capacity. Heat shock proteins (HSPs) are anti-apoptotic chaperone proteins, protecting against apoptosis under a variety of cell death stimuli including postmortem muscle conversion process. While a potential role of apoptosis in meat tenderization has been proposed, how early life stress influences apoptotic/proteolytic process and metabolism of postmortem muscles is largely unknown. Thus, the study objective was to evaluate apoptotic and proteolytic attributes and metabolomic changes in postmortem muscles of market weight pigs exposed to early life transport/weaning stress at two seasons.Materials and MethodsTwo repetitions of newly weaned pigs (N = 480) were transported for 12 h in a trailer truck during July 2016 (SUMMER) and April 2017 (SPRING) in north-central Indiana. Upon reaching market weight, 10 animals were randomly chosen from each season and slaughtered in January 2017 and September 2017, respectively. Pairs of longissimus dorsi and psoas major muscles from each carcass were separated at 1d and 7d postmortem. Proteolytic and apoptotic factors including desmin, troponin T, calpain 1, HSP27, and aβ-crystallin were quantified using Western-blot assays, and mitochondria membrane permeability (MMP) was evaluated. Metabolome profiles of 1d samples were analyzed using the GC-TOF-MS/MS platform. Multivariate analyses PCA and PLS-DA were used to determine changes of metabolites. Data were analyzed using PROC MIXED of SAS to compare the traits across season, muscle, and aging effects.ResultsPreviously, SUMMER pigs were reported showing decreased body weight, muscling, and fat deposition, as well as increased shear force and water loss during aging. In the present study, SPRING muscles exhibited increases in calpain 1 autolysis and structural protein degradation, coincided with accelerated apoptosis shown as higher MMP compared to the SUMMER counterparts (P < 0.05). Moreover, PCA and PLS-DA clustering indicated distinct metabolome profiles affected by season and muscle. Seasonal effect mainly altered lipid, glucose, and nitrogen metabolism. A group of 16C to 18C fatty acids were increased in SPRING, probably due to increased lipid anabolism during warm growing/finishing season. Changes of urea, ornithine, aspartic acid, and 5’methylthioadenosine suggested increased amino acid catabolism in SUMMER, corroborating the decreased lean and fat accretion. Seasonal changes of key metabolites related to stress response, including histidine, GABA, and ascorbic acid, suggested increased stress defense in SUMMER pigs, which implied the suppression of apoptotic and proteolytic activities.ConclusionTaken together, SUMMER pigs showed suppressed onset of apoptosis with compromised growth and meat quality, possibly due to alternations in seasonal metabolic response. This may in turn affect the proteolytic potential of early postmortem muscles. Further studies elucidating the involvement of apoptotic process in proteolytic activities in postmortem muscles should be warranted.

Efficacy of Beef Crust from Dry-Aged Beef Loins as Novel Functional Ingredient

ObjectivesDry-aging is a traditional butchery process, but currently, it has been more practiced in a niche market as a value-adding process. As dry aging involves placing primal/sub-primal sections under a controlled refrigerated condition without packaging materials, the formation of the dried surface (crust) is inevitable due to moisture evaporation. A considerable portion of the crust is to be trimmed off as waste, which is one of the major drawbacks of dry aging. While the beef crust may still exert its functional/technological properties, no information is available regarding the efficacy of utilizing beef crust as a potential food ingredient. Thus, the objective of this study was to determine the physicochemical and functional properties of beef crust from dry-aged beef loins processed under various dry-aging conditions.Materials and MethodsPaired bone-in beef shell loins from 13 cull cow carcasses (C-maturity) were obtained at 5d postmortem, divided into 2 sections and assigned to four aging treatments: wet-aging (WA), dry-aging (DA), dry-aging in water-permeable bag (DWA) and dry-aging under UV-light (UDA; 5 J/s/12 h per day). Beef sections were aged for 28d at 2°C, 65% RH and 0.8 m/s air flow. After aging, the crusts were separated and beef samples from WA and initial (aged for 0 d, INI) were collected for comparison. In three independent batches, the crust samples were freeze-dried and powdered. Moisture contents of samples were measured before lyophilization. Emulsification capacity, salt-soluble protein solubility, emulsifying activity index, and surface hydrophobicity were determined. CIE* color attributes, lipid oxidation (TBARS), and protein oxidation (carbonyl and thiol contents) were measured. The PROC MIXED procedure of SAS was used to analyze the data. Significance level of least square means was set at the confidence level of 95%.ResultsBeef crusts from dry-aged loins had lower moisture contents compared with WA and INI (P < 0.05), while no difference between dry-aging methods was found (P > 0.05). The crust samples had lower L* and chroma values than WA and INI (P < 0.05). Emulsification capacity of DA, DWA, and UDA were lower than WA and INI (P < 0.05), with DA being the lowest (P < 0.05). In general, the crust had a significantly higher salt-soluble protein solubility compared to WA, while no difference between crusts and INI was found (P > 0.05). For emulsifying activity index, DA exhibited higher values than DWA, UDA and WA (P < 0.05), and was comparable to INI (P > 0.05). DA and INI had higher surface hydrophobicity values than the other samples, which could possibly explain the results of emulsifying activity index. A trend of higher TBARS values was found in all dry-aged crusts than WA and INI (P = 0.0688). The crust from dry aging had a higher carbonyl content compared to WA (P < 0.05), while thiol contents were not affected by the treatment (P = 0.1092).ConclusionThe results from the current study indicate that beef crusts exert its functional and technological properties, which could be superior or at least equivalent to wet-aged or unaged beef samples. This study provides novel insight into the potential feasibility and utilization of beef crust from dry-aged beef as a value-added product. Further studies determining the practical application of beef crust as a novel food ingredient (e.g., meat emulsion or beef patty) are in progress.

Effects of probiotic (Bacillus subtilis) supplementation on meat quality characteristics of breast muscle from broilers exposed to chronic heat stress

The aim of this study was to determine the impact of probiotic feeding and chronic heat stress on meat quality, total lipid and phospholipid contents, lipid oxidation, antioxidant capacity, and heat shock protein abundance of broiler breast muscle. A total of 240 male broilers (5 birds per pen) were subjected to 4 treatments consisting of a 2 × 2 factorial design. Broilers were kept at 21-32-21°C for 10 h daily (heat stress, HS) or 21°C (thermoneutral condition) and fed a regular diet or the diet mixed with probiotic (250 ppm of Sporulin containing 3 strains of Bacillus subtilis). A total of 48 broilers (12 birds/treatment) were harvested at 46 d. Neither HS nor probiotic had substantial impacts on water-holding capacity, shear force, and color characteristics. HS induced lipid oxidation as increased 2-thiobarbituric acid reactive substances (TBARS), in which probiotic feeding decreased TBARS value (P = 0.002) and phospholipid contents (P = 0.0033) in breast muscle of HS broilers. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity was increased with HS (P < 0.0001), but no significant impact of probiotic supplementation was found. Neither probiotic nor HS affected catalase activity, but superoxide dismutase and glutathione peroxidase activities were lower in HS broilers compared to thermoneutral controls (P < 0.0001) and in probiotics-fed broilers (P < 0.0001) compared to their counterparts. In addition, a significant interaction between probiotic and HS was found at glutathione peroxidase activities, in which breast muscle of broilers fed probiotic at thermoneutral condition showed the highest activity (P < 0.05). Regarding heat shock protein (HSP) determination, HS slightly increased the levels of both HSP70 (P = 0.08) and HSP27 (P = 0.05), but no significant impacts of probiotic supplementation were found. Our results indicate that probiotic feeding could improve breast muscle weight without adverse impacts on meat quality attributes, as well as alleviate oxidative deterioration of breast muscle of broilers undergoing heat stress.

Effects of probiotics feeding on meat quality of chicken breast during postmortem storage

This study evaluated the effects of dietary probiotic supplement and postmortem storage on meat quality of chicken breast during retail display. A total of 35 birds were randomly obtained from 3 feeding groups (control without probiotic supplement, 250 ppm Sporulin, and 500 ppm PoultryStar). The probiotic supplement had no influence on feed conversion ratio and body weight gain, as well as body weight at 29 and 44 d (P > 0.05). After slaughter, each side of the breast muscles (M. Pectoralis major) was assigned to either one d or 5 d of postmortem storage. Probiotic supplement had no influence on the rate of pH decline of chicken breast muscles during the initial 6 h postmortem (P > 0.05). No interactions between probiotic supplement and postmortem storage on meat quality were found (P > 0.05). Postmortem storage decreased drip loss from 25.30 to 18.05% (P < 0.05). Probiotics-fed chicken groups, particularly PoultryStar treatment, had a higher myofibrillar fragmentation index than the control group (P < 0.05). However, shear force values were not affected by the probiotic treatments. Decreases in color and lipid stabilities of breast muscles were found during display (P < 0.05), but were not affected by the probiotic supplement (P > 0.05). Our result suggests that probiotic supplement had no adverse impacts on proteolysis and oxidative changes during 5 d postmortem display storage.

Pre-rigor carcass stretching counteracts the negative effects of high rigor temperature on tenderness and water-holding capacity – using lamb muscles as a model

High pre-rigor muscle temperature has negative consequences on quality and has been predominantly studied in the excised longissimus muscle of beef and lamb carcasses. There is little data on other muscles, the application in whole carcasses or potential amelioration techniques such as stretching. This study evaluated the effects of electrical stimulation, high pre-rigor temperature and stretching of lamb sides on quality traits and protein denaturation in four leg muscles [gluteus medius (GM), rectus femoris (RF), semimembranosus (SM) and semitendinosus (ST)]. Twenty lamb carcasses were used with two electrical stimulation treatments (stimulated or non-stimulated, +/−) and two pre-rigor temperature treatments (chilled at 2°C directly after slaughter, or held in 37°C water for 4.5 h before transfer to a 2°C chiller) applied. One side of each carcass was suspended from the Achilles tendon, whereas the other side was stretched by allowing the leg to drop and tying it to the ribs. Electrical stimulation did not influence the different traits except for pH fall post slaughter and myosin denaturation. Stretching resulted in greater muscle and sarcomere lengths for the GM, SM and ST, but a decrease in sarcomere length for the RF. For the non-stretched GM and SM, the 37°C treatment resulted in tougher meat at 1 and 8 days post mortem compared with the 2°C treatment. In contrast, the stretched 37°C treatment resulted in more tender meat for the GM, SM and ST at 1 day post mortem compared with the 2°C treatment. For all muscles, the 37°C treatment resulted in a decrease in the water-holding capacity (increased purge, surface exudate and cooking losses). The magnitude of this effect was generally diminished by stretching for the GM, SM and ST, but for the RF, (which was not stretched by the treatment) this effect was reversed. The 37°C treatment resulted in paler meat (increased L*-values) for the GM, SM and ST relative to the 2°C treatment. The observed effects of the 37°C treatment on water-holding capacity and colour could be explained by the effects of this treatment on indicators of protein denaturation (sarcoplasmic protein solubility and myofibrillar ATPase activity), which were decreased for the GM, SM and ST. The response to both temperature and stretching varied between the muscles, due to different anatomical location and also due to postulated differences in the fibre types. In conclusion, pre-rigor stretching of lamb sides can counteract the negative effects of high early post-mortem temperature on tenderness and water-holding capacity for those muscles that are stretched as a result of this hanging method.

Impacts of hanging method and high pre-rigor temperature and duration on quality attributes of ovine muscles

This study evaluated effects of high pre-rigor temperature and duration and suspension of lamb sides on quality traits and protein denaturation in two muscles [semimembranosus (SM) and longissimus thoracis et lumborum (LTL)]. Twenty-four lamb carcasses, within each of 3 slaughter days, were used to assign eight carcasses to one of four pre-rigor temperature treatments: chilled at 2°C directly after slaughter, or held at 37°C in water for 1.5, 3.0 or 4.5 h before transfer to a 2°C chiller. At ~15 min post slaughter, one side of each carcass was suspended from the Achilles tendon, whereas the other side was suspended by the aitch bone and the leg tied down to the ribs. The sides subjected to aitch bone hanging had an increased sarcomere length in the SM, but decreased sarcomere length in the LTL. For the LTL, the time of exposure to high pre-rigor temperature had a significant effect on measures of protein denaturation and related meat quality traits such as purge and colour, although tenderness (shear force) after 2 days of aging was not affected. For the SM, the high temperature treatment also resulted in increase in measures of protein denaturation and thus negatively influenced meat quality traits such as purge, colour and shear force after aging. However, these effects on purge and shear force in the SM were significantly mitigated by the aitchbone hanging treatment. The results of the present experiment indicate that pre-rigor aitchbone hanging of muscles can counteract the negative effects of high pre-rigor temperature on both water loss and meat tenderness.

Effect of forage and retail packaging types on meat quality of long-term chilled lamb loins

The objectives of this study were to determine the effects of different forage regimes and modified atmosphere packaging (MAP) systems [high oxygen (HiOx-MAP): 80% O2 and 20% CO2; and CO2-MAP: 20% CO2 and 80% N2] on color and lipid oxidation stability and sensory attributes of long-term chilled lamb loins during retail display. Lambs (n = 124) were randomly assigned to several pasture-feeding regimes for 12 wk before slaughter. Some had ryegrass (n = 18), lucerne (n = 18), chicory (n = 19), plantain (n = 16), or red clover (Clover 12; n = 17) for all 12 wk. Some were assigned a regime of red clover for 11 wk and pasture for 1 wk (Clover 11; n = 18), with others on red clover for 9 wk and pasture for 3 wk (Clover 9; n = 18). After the lambs were slaughtered, the paired loins (M. longissimus dorsi) were excised at 24 h postmortem, vacuum-packed and stored at -1.5 °C for 9 wk. Cuts were then made from each loin and randomly allocated to either HiOx-MAP or CO2-MAP, and displayed for 7 d at 4 °C under light. Chemical attributes including lipid oxidation, surface color-reversing ability, oxygen consumption, and meat quality attributes (color stability and sensory characteristics) were determined. Among the different forage types, the loins from lambs finished on ryegrass appeared to have greater color stability and less lipid oxidation than the loins from lambs finished on other forage types (P < 0.05). On the other hand, the loins from lambs finished on lucerne had the least color and lipid oxidation stabilities and least color-reversing ability (P < 0.05). The loins from lambs finished on chicory had higher aroma and flavor scores than other pasture types in general (P < 0.05). HiOx-MAP negatively influenced meat quality attributes of lamb loins during display, as substantial increases in surface discoloration and lipid oxidation were observed, along with significant decreases in aroma and flavor during retail display compared with the loins in CO2-MAP. These results suggest that different forage types and packaging conditions could result in substantial impacts on meat quality attributes of long-term chilled lamb loins by affecting oxidation stability. Furthermore, the present study suggests that CO2-MAP could provide beneficial effects on the eating quality of long-term chilled lamb loins by suppressing oxidation-related defects during display without compromising the ability of blooming for meat display.

Effect of low voltage electrical stimulation on protein and quality changes in bovine muscles during postmortem aging

This experiment was conducted to determine the influence of low voltage electrical stimulation (ES) on the tenderness development of beef round muscles. Eight steers were slaughtered, and ES applied to one side of each carcass within 90 min of exsanguination. Steaks from M. longissimus dorsi, semimembranosus, adductor, and gracilis were vacuum packaged and aged at 4 °C for 9 d. Star probe, sensory evaluation, Western blot assays of troponin-T and μ-calpain autolysis and 2D-DIGE were conducted. ES resulted in accelerated (P<0.05) pH decline of the longissimus in the first 24h postmortem. ES did not influence (P>0.05) proteolysis and tenderness, but did alter the predominance of metabolic proteins in the soluble fraction of muscle. Aging for 9 d improved tenderness (P<0.05). The data confirmed that low voltage ES at 90 min of exsanguination had no effect on proteolysis and tenderness development in the longissimus dorsi, semimembranosus, adductor or gracilis in beef.