Reducing Postmortem Aging Time of Beef with Electrical Stimulation

Two studies (Study 1 = 23 forage-fed steers; Study 2 = 20 grain-fed steers and heifers) were conducted to determine relationships of electrical stimulation (ES) and/or postmortem aging (PA) to tenderness of beef. For Study 1, steaks from ES sides had lower (P < 0.05) Warner-Bratzler shear (WBS) values than steaks from not-ES sides for each PA period. In addition, the percentage reduction in WBS values was greater for the steaks from the ES-Day 2 group (–29.5%) than for steaks from even the longest PA period (14 days) from the not-ES group (–25.8%). For Study 2, during the fist three PA periods (1, 2 and 5 days), ES resulted in more desirable (P < 0.05) flavor ratings (Day l), higher (P < 0.05) tenderness ratings and lower (P < 0.05) WBS values (Day 1, 2, 5) and more desirable (P < 0.05) overall palatability ratings (Day 1, 2). During the last three PA periods (8, 11 and 14 days), ES resulted in higher (P < 0.05) tenderness ratings (Day 8), lower (P < 0.05) juiciness ratings (Day 11, 14) and lower (P < 0.05) WBS values (Day 8). Based on these results, ES had the greatest impact on beef palatability if the period of aging was 8 days or less; with additional aging time, ES effects on palatability were negated. When each treatment (ES, not-ES) was divided into two groups based on median tenderness ratings for the not-ES group, ES had the greatest impact on those carcasses in the “tough” group while ES had little impact on those carcasses in the “tender” group. ES will accelerate the postmortem aging of beef but the aging time reduction and extent of ultimate tenderization appears to be affected by the inherent tenderness of the beef.     

Quadratic relationship between early-post-mortem glycolytic rate and beef tenderness

Post-mortem (PM) glycolytic rate in beef M. longissimus thoracis et lumborum (LTL) was controlled by applying low-voltage electrical stimulation (ES) for 1 min at different stages along the slaughter line. The ES treatments were as follows: (1) No electrical stimulation (NES); (2) 75 V to one side of the carcass immediately after splitting; (3) 20-40 V during exsanguination; (4) 75 V either during or following exsanguination. The study utilized 40 bulls and 40 steers. Loin steaks were aged in vacuum pouches 2, 4, 8 and 16 days PM. Quadratic equations utilizing pH at 3 h (pH(3)) gave the best estimate of Warner-Bratzler (WB) shear force for 2, 4, 8 and 16 day steaks. The rate of glycolysis is the primary determinant of LTL tenderness in this study. Temperature may only be important through its influence on early PM glycolytic rate. Optimum tenderness was produced by stimulating carcasses or sides to produce a pH(3) of 6·0. ES application to the carcass either just before or after splitting (treatment 2) produced more desirable and consistent pH(3) responses than either NES or ES during exsanguination. Aging has a differential effect whereby the WB shear values from tougher (leaner bulls) 2 day steaks improve to a greater degree, so they are not different from more tender (fatter steers) steaks by 16 day PM.     

A procedure to determine the water-binding capacity of meat trimmings for cooked sausage formulation

Eight bovine muscles were evaluated to determine if perimysium thickness (PT) differed among muscles and carcasses and was affected by electrical stimulation (ES). In addition, the effect of PT on Warner-Bratzler shear (WBS) of steaks divided into tenderness groups was evaluated. Muscle and carcass affected (P<0.05) PT, but PT was not significantly affected by ES. Correlation coefficients revealed that PT would be a poor indicator of WBS when used alone (r=0.13). When analyzed within electrical stimulation treatment, PT was correlated (P<0.05) to WBS of NES (r=0.21) carcasses and not significantly related to WBS of ES carcasses. Within tenderness groups, PT accounted for 4.5%, 9.5%, 20.0%, and 4.0% of the variation in WBS force at 3, 7, 14, and 21 d, respectively. These results indicate that PT can be used in conjunction with other myofibrillar components of tenderness to account for some variation in WBS values of cooked beef steaks.     

IDENTIFICATION OF THRESHOLD LEVELS FOR WARNER-BRATZLER SHEAR FORCE IN BEEF TOP LOIN STEAKS

Threshold Warner-Bratzler shear (WBS) values were determined by regression analysis of WBS force values and trained sensory panel overall tenderness ratings of beef top loin steaks from A- and B-maturity carcasses (n = 678). Guidelines for retail and foodservice beef were based on 50 and 68% confidence levels, respectively, for overall tenderness ratings of "slightly tender." Due to the extreme variation in tenderness that exists in the current U.S. beef population, more stringent confidence levels were not practical. Threshold WBS values for retail and foodservice beef were 4.6 and 3.9 kg, respectively. When these values were tested against the population of beef in the National Consumer Retail Beef Study, the 4.6 kg value was 88.6% accurate at determining whether or not a steak would be rated less than "slightly tender"by consumers.     

Effects of electrical stimulation, chilling temperature and hot-boning on the tenderness of bovine muscles

The objective of this study was to determine the effects of hot-boning, low voltage electrical stimulation (ES) and chilling temperature on the tenderness of bovine M. longissimus dorsi (LD) and M. semimembranosus (SM) muscles. LD (n=32) and SM (n=32) muscles were subjected to different post-mortem treatments; hot-boning (before 90min post-mortem), cold-boning (at 48h post-mortem), low voltage ES and rapid or slow chilling. Hot-boned muscles which were not electrically stimulated (NES) had higher Warner Bratzler shear force (WBSF) values (P<0.001) and shorter sarcomeres (P<0.001) than cold-boned muscles. Hot-boned muscles subjected to ES had lower pH values (P<0.001) post-stimulation and up to 8h post-mortem than NES muscles. At both chilling temperatures WBSF values were lower in ES hot-boned LD and SM muscles at days 2, 7 and 14 post-mortem than NES muscles. Hot-boned muscles subjected to slow chilling had longer sarcomeres (P<0.001) than those subjected to fast chilling. In hot-boned SM muscles, ES resulted in longer sarcomere lengths (P<0.001). However, ES did not have a significant effect on the sarcomere length of LD muscles. As indicated by WBSF values all muscles tenderised during ageing, including muscles which were 'cold shortened'. Proteolysis was not the main reason for differences in WBSF values between ES and NES muscles as judged by qualitative sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). A combination of slow chilling and ES had a positive effect on hot-boned muscles with respect to WBSF values.     

Relationship of texture profile analysis and Warner-Bratzler shear force with sensory characteristics of beef rib steaks

Cyclical texture profile analysis (TPA) parameters measured using a star-shaped probe with two cycles of 80% penetration and Warner-Bratzler shear force (WBS) were compared as predictors of objective tenderness and subjective sensory characteristics of rib steaks from 52 beef loins. The TPA parameters of hardness, cohesiveness and chewiness were negatively correlated (P<0.05) with trained panel sensory characteristics of initial tenderness (r=−0.64, −0.41, −0.62, respectively), amount of connective tissue (r=−0.57, −0.27, −0.55, respectively), overall tenderness (r=−0.68, −0.39, −0.64, respectively) and overall palatability (r=−0.56, −0.37, −0.53, respectively). These sensory characteristics were also negatively correlated (P<0.05) with WBS (r=−0.61, −0.49, −0.60, −0.56, respectively). Stepwise regression analysis generated prediction equations that included the TPA parameters of hardness and adhesiveness, which accounted for 47, 36, 51 and 38% of the variation in initial tenderness, amount of connective tissue, overall tenderness and overall palatability, respectively. Prediction equations using WBS accounted for 37, 24, 36 and 31% of the variation in initial tenderness, amount of connective tissue, overall tenderness and overall palatability, respectively. Hence, TPA explained more of the variation in subjective sensory tenderness of the rib steaks than WBS.     

RELATIONSHIP OF USDA QUALITY GRADES TO PALATABILITY OF COOKED BEEF1

Prime carcasses produced loin and round steaks that were more palatable (P < 0.05) than were those from carcasses of Choice through Canner (7 grades) in 85.7% of comparisons and from carcasses of Choice through Standard (3 grades) in 69.0% of comparisons; comparable percentages were 71.4% (6 grades) and 42.9% (2 grades) for Choice and 74.3% (5 grades) and 35.7% (1 grade) for Good. Among Prime through Standard carcasses, grade predicted flavor, tenderness and overall palatability of loin steaks with 30 to 38% accuracy, but could explain no more than 8% of the variation in panel ratings/shear force values of round steaks.     

Palatability characteristics of loin steaks from Charolais crossbred bulls and steers

Loins from 1/2-blood or 3/4- to 7/8-blood Charolais bulls (n = 60) and steers (n = 64) were obtained at 24 h post mortem from electrically stimulated sides and, at 12 days post mortem, steaks were removed and frozen. Shear force values were higher (P < 0·001) and sensory panel evaluations of tenderness and overall palatability were lower (P < 0·001) for steaks from bulls than from steers. No differences (P > 0·05) in connective tissue amount or off-flavour were detected for steaks from bulls versus steers. Significant correlations between carcass secondary sex characteristics and sensory panel evaluations of tenderness were noted, but the coefficients were not of a magnitude to be considered predictive of tenderness.     

Processing Properties of Beef Semimembranosus Muscle as Affected by Electrical Stimulation and Postmortem Treatment

Semimembranosus muscles from paired sides-electrically stimulated (ES) and not-stimulated (NES)-of mature cows were used to determine effects of certain postmortem treatments (state of rigor/temperature) and of ES on processing properties. ES decreased (P<0.05) pH values for prerigor, prerigor/frozen and postrigor/frozen muscles, but did not affect (P>0.05) values for total protein or juice loss during cooking. State of rigor/temperature treatment affected pH and salt-soluble protein (SSP) values more than did ES treatment. pH values differed (P<0.05) between each state of rigor/temperature treatment for both ES and NES samples. Salt-soluble protein values were higher (P<0.05) for NES prerigor than for NES postrigor/frozen samples and higher (P<0.05) for NES postrigor than for NES postrigor/frozen samples. SSP values for ES muscles were higher (P<0.05) for ES postrigor samples than for ES postrigor/frozen samples but were not different for other comparisons. Regardless of ES treatment, freezing of semimembranosus muscles increased pH values (P<0.05) and decreased SSP values (P<0.05) in three of four comparisons.     

Effects of early-postmortem glycolytic rate on beef tenderness

Electrical stimulation (ES) was applied at 500 V to one side from each of 60 beef carcasses at 30 to 40 min postmortem. Wide ranges of early-postmortem glycolytic and cooling rates were produced in the musculature by use of three different forms of ES (in addition to non-ES treatment of the contralateral sides) and application of chilling routines of four different degrees of severity. Panel and Warner-Bratzler shear evaluations of loin steaks from all 120 sides showed that tenderness was highest when glycolysis had proceeded at an intermediate rate (corresponding to the attainment of a 3-h pH of about 6·1) and was appreciably lower on both sides of this mid-value. The toughening effect of rapid glycolysis (relative to that of a moderately increased glycolytic rate) persisted through 14 days of aging at 2°C.

These observations appear to be incompatible with the view that lysosomal enzymes contribute significantly to ES-induced tenderization. They also indicate that the effect of ES on tenderness is highly dependent on the subsequent cooling rate, very slow chilling sometimes accelerating the already high rate of pH fall to such an extent that the tissue is significantly toughened. Finally, they suggest that the goal of maximizing the early-postmortem rate of pH decline in bovine muscle is misguided and, if attained, will cause sub-optimal tenderness.     

Effects of Rapid Processing on the Chemical and Sensory Properties of Restructured Steak Made From Bull and Steer Meat

South Devon cattle (10 bulls, 10 steers) were slaughtered to determine effects of sex condition and postmortem temperature conditioning on the chemical and sensory properties of restructured beefsteak. Chucks from each left side were boned following a 4 hr delayed chill (DC, 13°C) period, while chucks from right sides were boned following a 48 hr conventional chill (CC. 2°C). Chucks were mechanically tenderized and formulated into restructured steaks. Bulls produced restructured steaks less prone to oxidative rancidity. Restructured steaks from bulls exhibited higher (P<0.01) cooking losses and Kramer Shear values. There were no differences between treatments in tenderness, juiciness, flavor, and connective tissue residue ratings; however, DC restructured steaks had lower (P<0.05) bind values than CC restructured steaks.     

Quality, palatability and weight loss of pork as affected by electrical stimulation

Forty-five swine (n = 15, stress-susceptible pigs, fasted for 18 h; n = 15, normal pigs, fasted for 48, 60 or 72h; n = 15, normal pigs, fasted for 18 h) were slaughtered. One side of each pig was electrically stimulated (ES)-550 V, 2-6 A, seventeen impulses, 1·8 s on and 1·8 s off per impulse-and the opposite side was not stimulated (NS). Ham and loin temperatures were monitored at 12 and 24 hours post mortem. Carcass quality-marbling, loin eye colour, loin eye firmness, subcutaneous fat firmness and belly firmness-was evaluated at 24 hours post mortem. Sides were fabricated into four lean cuts at 48 hours; cuts were placed on open metal racks in a 2°C cooler and weight loss was measured after 24, 48 and 72 hours storage. At 120 hours post mortem, loin chops were cut, frozen (-24°C for 45 days) and subsequently used to determine thaw loss, cooking loss, Warner-Bratzler shear (WBS) force and palatability. Ham temperatures (12 h) were significantly (P < 0·05) lower for the ES sides from the stress-susceptible, short-fast (SSF) group but not for normal, long-fast (NLF) or normal, short-fast (NSF) groups. ES produced lighter coloured, softer loin eyes in the SSF group but darker coloured, firmer loin eyes and firmer subcutaneous fat in the NLF group. No significant differences (P > 0·05) were detected for thaw loss, cooking loss, palatability ratings or WBS values between ES and NS in the SSF group but chops from ES sides of NLF animals had significantly (P < 0·05) higher ratings for muscle fibre tenderness, overall tenderness and overall palatability. Weight losses of the lean cuts from the ES sides were higher (P < 0·05) than those from NS sides in only three of sixty comparisons of cuts from the three groups of swine. These data suggest that ES had very minimal effects on quality, palatability or weight loss of pork.     

Should electrical stimulation be applied when cold shortening is not a risk?

This experiment was designed to show whether delayed high voltage stimulation (ES) is more beneficial than no stimulation (NS) to secure tenderness under circumstances where rigor conditions are difficult to control due to variations in carcass size, fatness and/or chilling capacity. Ten Charolais carcasses were split during slaughter, the left sides were stimulated at 45 min post-mortem for 45 s, and the right sides were left unstimulated. The carcass sides were then chilled at a medium chilling rate. Sarcomere length measurements confirm that there was neither cold nor heat shortening in the M. longissimus (LD). LD from ES sides aged for 2 days was more tender than non-stimulated LD (NES), although prolonged ageing eroded the advantage of ES to a non-significant advantage after 14 days. Initial tenderness differences coincided with lower 24 h calpain activity, suggesting an early onset of proteolysis and ageing (tenderisation). In contrast to conventional early ES, delayed ES, appears to be beneficial for the early development of tenderness without too much interference with enzyme. Myofibril fragment length (MFL) was a good indicator of the development of tenderness during prolonged ageing but not for the early post-mortem variation in tenderness. No colour (L*, a*, b*) differences, occurred due to stimulation treatment, while drip loss was slightly higher at 24 h post-mortem for ES meat.     

Effects of Preslaughter Exercise, Electrical Stimulation, Type of Packaging Tray, Display Temperature, and Time on Acceptance and Shelflife of Beef Steaks

Eight steers, of which four were exercised prior to slaughter, were slaughtered and one side of each carcass electrically stimulated (ES). Steaks from combined wingrib and sirloin were packaged in two types of plastic foam trays, overwrapped with PVC and displayed in refrigerated display cabinets either at 0°C or 5°C meat surface temperature. Display temperature and period of display significantly influenced shelflife and overall appearance of steaks. ES enhanced tenderness and improved muscle color but caused more weight loss during display when compared with steaks from unstimulated carcasses. All factors investigated had a significant influence on percentage weight loss during display while stress and tray depth also negatively influenced cooking weight loss encountered during cooking.     

Characterization of cutability and palatability attributes among different slaughter groups of beef cattle

Fifteen slaughter cattle from five groups (Charolais crossbred bulls, Brahman crossbred steers, Holstein steers, mixed-Exotic crossbred heifers and Hereford-Angus crossbred steers) were randomly selected from a commercial feedlot. Time-on-feed was 108, 114, 102, 108 and 145 days for the aforementioned groups, respectively. Carcasses from Charolais crossbred bulls had the highest percentage yield of chuck and round, but the lowest percentage yield of loin; hereford-Angus crossbred steers had the lowest percentage yield of round and Holstein steers had the lowest percentage yield of rib. Carcasses from Charolais crossbred bulls had the highest percentage yield of major retail-ready subprimals and lean trim, Hereford-Angus crossbred steers had the highest percentage yield of fat trim and Holstein steers had the highest percentage yield of bone from the major wholesale cuts. Mean percentage yields of closely trimmed, boneless retail cuts were highest for carcasses from the bulls and lowest for carcasses from the Hereford-Angus steers. Although Holstein steer carcasses had less fat trim than Brahman-crossbred steers mixed-Exotic heifers, this advantage was largely offset by their higher percentage of bone. Loin steaks from carcasses of Charolais crossbred bulls, Holstein, mixed-Exotic heifers were comparable (P > 0·05)with those of Hereford-Angus steers for shear force and sensory panel tenderness ratings. However, loin steaks from carcasses of Brahman-crossbred steers had significantly higher (P < 0·05) shear force values (least tender) and lower (P < 0·05) tenderness and overall palatability ratings. No diffeerences (P > 0·05) were found for flavor desirability of loin steaks among any of the groups. For bottom round steaks, Hereford-Angus steers received the highest palatability ratings while those from Holstein steers received the lowest palatability ratings.     

Effects of Beef Carcass Electrical Stimulation, Hot Boning, and Aging on Unfrozen and Frozen Longissimus dorsi and Semimembranosus Steaks

Ninety-six sides from 48 beef carcasses were used to study the effects of hot boning (HB), electrical stimulation (ES), a combination of electrical stimulation and hot boning (ESHB), and steak storage treatments on longissimus dorsi and semimembranosus steaks. Steak storage treatments were: unfrozen (aged until 6 days postmortem) or frozen (ES, HB, and ESHB frozen 24 hr and controls 48 hr postmortem). ES did not improve taste panel ratings or consistently lower shear force values when compared with control counterparts. Storing carcasses at 5°C for the first 24 hr postmortem and freezing ES steaks at 24 hr versus 48 hr postmortem for the control possibly diluted the effectiveness of ES. However, ES did eliminate any toughening due to HB.     

MECHANICAL MEASUREMENTS OF MEAT TENDERNESS USING THE NIP TENDEROMETER

Abstract. A series of evaluations to compare the sensory panel ratings for tenderness with the Warner-Bratzler shear force and the Nip Tenderometer values was conducted using 150 pork chops, 239 lamb chops and 674 beef steaks. The Warner-Bratzler shear force values were more highly correlated with panel tenderness ratings than were the Nip Tenderometer readings for samples of pork, lamb and beef tested after cooling to room temperature (23 °C). Nip Tenderometer determinations on hot samples of beef (75 °C) were more closely related to panel tenderness ratings ( r =— 0.80) than were Nip Tenderometer readings ( r =— 0.58) or shear force values ( r =— 0.63) obtained on cold samples (23 °C). The combined advantages of ease and speed of application, correlation with sensory panel ratings and the demonstrated accuracy in identifying 'tough' vs 'tender' steaks suggest that the Nip Tenderometer has potential as an objective means for evaluating meat tenderness.     

Concentration of Creatine Phosphate, Adenine Nucleotides and Their Derivatives in Electrically Stimulated and Nonstimulated Beef Muscle

The concentration of creatine phosphate (CP), adenosine tri-, di- and monophosphate (ATP, ADP and AMP, respectively), inosine monophosphate (IMP) and inosine in longissimus muscle removed from electrically stimulated (ES) and nonstimulated (NS) beef sides was enzymatically determined. After aging the carcass 7 days, steaks were removed for flavor evaluation. R values (absorbance ratios) were obtained from muscle samples removed over time from both sides. Data indicate more rapid catabolism of CP, ATP, and ADP in ES samples, with subsequent fluctuations in IMP and inosine concentration. At 12 and 24 hr post-stimulation, ES samples had more inosine; however, this difference did not exist after aging. Flavor differences were not observed after the 7-day aging period. R values parallel the degradation of adenine nucleotides and indicate rapid onset of rigor mortis in ES muscle.     

INCREASING THE TENDERNESS OF BULLOCK BEEF BY USE OF ANTEMORTEM ENZYME INJECTION

Steaks from 58 beef carcasses were used to determine the effects of antemortem injections of proteolytic enzyme in increasing tenderness and/or in reducing tenderness variability among bullock carcasses. Sensory panel ratings indicated that steaks from the carcasses of treated bullocks did not differ significantly from steaks from treated steer carcasses in tenderness or overall satisfaction, but were significantly more tender and satisfactory overall than steaks from untreated bullocks. Variation in tenderness scores within the group of steaks from treated bullocks was reduced to a level more nearly comparable to that of steaks from treated steers. Since antemortem injections of papain increased tenderness and reduced the variability in tenderness among steaks from bullock carcasses, such treatment could be used to more effectively merchandise beef from young bulls.     

RETAIL APPEARANCE OF ELECTRICALLY STIMULATED BEEF

Top round steaks (adductor) and ground beef from the top round were obtained from both sides of ten U.S. Choice carcasses. Left sides were electrically stimulated (ES) with 17 impulses (1.8 set duration, 1.8 set interval) of 550 volts of alternating current at 5 amps. Steaks and ground beef from top rounds from nonstimulated right sides served as control (CON) samples. Steaks and ground beef were displayed under simulated retail conditions for 4 and 3 days, respectively. Steaks were weighed prior to and at the termination of the display interval to determine percentage weight loss. Samples for microbiological evaluation were obtained prior to and at the termination of the display interval. No significant differences were observed for muscle color, surface discoloration or overall appearance for samples of ground beef at any retail display interval. With one exception, muscle color was brighter and surface discoloration was reduced for round steaks from ES sides. Few significant differences in overall appearance were observed between ES and CON samples during the display period. No significant differences between ES and CON samples were observed for bacterial counts either initially or at the termination of the display period for either steaks or ground beef samples. Percentage weight loss was not significantly different between ES and CON steaks. These data suggest that electrical stimulation may enhance, and certainly does not detract from, the appearance of round steaks displayed under retail market conditions.