IBC2000-6 Meat Information

Bison:  Meating the Beef Challenges

Dr. Jennifer L. Aalhus
Agriculture & Agri-Food Canada
Lacombe Research Centre
6000 C & E Trail
Lacombe  AB   Canada   T4L 1W1

Jennifer A.M. Janz, PhD Candidate
Department of Agriculture, Food and Nutritional Science
University of Alberta
Resident at the Lacombe Research Centre

The following article was originally presented at the International Bison Conference in Edmonton, Alberta in August 2000.  The conference covered a wide array of bison topics including production, marketing, genetics, history and much more.  This article has been reprinted with the permission of the IBC2000 Chairman.

Abstract

As defined by its role as a function tissue in the live animal, muscle (meat) has a similar structure across species.  In order to successfully market its products as unique and at a premium over beef, the bison industry must carefully examine and capitalize on the challenges facing the beef industry.  To avoid the production of expensively finished, overfat carcasses grown to satisfy the grading system, modification to the current bison grading system or development of a branded product marketing system could help to maintain the image of bison as a "naturally produced".  Variability in eating quality can be controlled with the application of postmortem carcass technologies designed to enhance tenderness.  Rather than marketing the carcass as a bulk commodity, a move towards value-based marketing would see the carcass treated as a collection of unique components each suitable for its own ideal purpose.  With attention focused on previous and current issues affecting beef, and with an eye on the scientific advances in meat quality improvement, the bison meat industry may benefit from the beef industry experience and reap the benefits of the careful application of this knowledge.

Keywords

Muscle structure, bison meat quality, tenderness, postmortem carcass technologies

Introduction

As a live animal, bison are easily distinguishable from cattle.  Bison are the wooly ones with a big hump on their neck; cattle generally lack the wool and the hump.  As a carcass, most people would still be able to pick out the characteristic hump on a bison carcass.  However, at the level of a steak, it is much harder to decide whether the meat comes from bison or beef.  Despite some slight differences, both bison meat and beef are quite similar at the cellular level.  Logically, muscle tissue cannot have huge variations in structure and composition without affecting its functionality in the live animal.  Despite being a very similar protein source, bison meat presently commands a large price differential compared to beef (100-300% more for high value cuts).  In order to continue to command premium prices, the bison industry needs to capitalize on the lessons learned from challenges currently facing the North American beef industry.

The Basics of Muscle and Meat

Muscle, is a functional tissue, with its main purpose to facilitate movement and maintain posture in a live animal.  The force generated through muscular contraction is transmitted through connective tissue to the tendons, causing movement of the bones.  In general, muscles with a greater role in locomotion (those attached to the head and limbs) have more connective tissue.  Muscles that function mainly in posture control, for example along the backbone, have far less connective tissue.  Ergo, the lower and higher value meat cuts.

At the cellular level, a muscle fibre (cell) is composed of a number of parallel fibres, called myofibrils that contain the contractile proteins in a series of repeating units called sarcomeres.  The major contractile proteins consist of thick myosin molecules, thin actin molecules and regulatory proteins (troponin and tropomyosin).  In addition to the contractile proteins the muscle fibre contains many organelles including the mitochondria (responsible for energy production), the sarcoplasmic reticulum (a membrane system which sequesters calcium), glycogen particles (energy storage deposits composed of multiple glucose units), nuclei (containing the genetic information of the cell) and various other enzymes and proteins.

Muscle contraction is initiated by delivery of a chemical message from the nervous system to the membrane surrounding each muscle fibre.  The chemical message is transmitted along the membrane and through tubules to the sarcoplasmic reticulum at the interior of the cell.  Upon receiving the message, stored calcium is released from the sarcoplasmic reticulum into the interior of the cell.  Free calcium binds to the regulatory protein, troponin, causing a slight shift in the location of tropomyosin, exposing sites where myosin can interact with actin.  Myosin heads form crossbridges with the actin and then shift their head angle, causing the actin filaments to slide past the myosin towards the center of the sarcomere.  This reduces the length of the sarcomere, and when this occurs at the same time throughout many thousands of sarcomeres in the muscle, movement at the gross level occurs.  The energy source fueling contraction comes from adenosine triphosphate (ATP), which is responsible for activating the shift and concomitant release of the myosin head.  ATP is produced through the metabolism of glucose (sugar), either in the presence of oxygen (aerobic metabolism yielding 36 ATP) or without oxygen (anaerobic metabolism yielding 2 ATP).  When oxygen is present glucose is completely metabolized producing carbon dioxide and water as end products.  When no oxygen is present the end product of glucose degradation is lactic acid.

To a muscle cell, the most significant event at slaughter is the loss of the circulatory system.  Without circulation of blood, the muscle cell receives no oxygen or blood glucose and has no capacity to rid itself of waste products.  In an effort to maintain homeostasis, the muscle cell switches to anaerobic metabolism and utilizes stored glycogen as a source of ATP.  Lactic acid accumulates, causing a slow acidification of the cell with a resulting decline in pH.  Under the developing acid conditions, cellular processes slow down and membrane integrity is compromised.  Since the membrane is no longer able to effectively compartmentalize the calcium ions, an influx of calcium occurs causing multiple myosin/actin linkages to form.  At the same time, the concentration of ATP has been depleted to a level insufficient to free all the linkages.  Myosin heads become permanently locked to the actin and rigor mortis (stiff death) occurs.

Out of this background information, there are some important points.  Firstly, as a functional tissue in the live animal, the structure and composition of muscle must remain relatively fixed to ensure its functionality.  Hence bison meat must be quite similar to beef.  Secondly, the process of conversion from muscle to meat occurs over the 24-48 h immediately post-slaughter.  During this biochemically active time period, there are a number of ways to effectively influence the final meat quality.  Finally, the function and form of individual muscles in the live animal contribute to a wide variety of “muscle qualities” on every carcass.  These inherent differences should be viewed as opportunities to produce value-added products.

Differences between Bison Meat and Beef

Although we indicated muscle tissue remains relatively static in order to be functional, some differences between bison meat and beef do exist.  As part of her graduate studies, Jennifer Janz has been characterizing some of the differences between bison and beef, as meat animals.

Carcss Traits

In general, bison have similar dressing percentages (hot carcass weight as a proportion of liveweight), slightly higher cooler shrink, and a higher proportion of saleable yield than beef.  In our studies bison ranged in dressing percent from 55.7 to 61.9%.  Aalhus et al. (1992)  reported a range from 58.6 to 61.8% for beef carcasses from cattle raised on diverse feeding regimes.  Cooler shrink losses in bison carcasses from our studies ranged from 0.98 to 2.25%.  Aalhus et al. (1992)  reported mean cooler shrink loss values ranging from 1.14 to 1.62% for the beef carcasses previously discussed.  The tendency for bison carcasses to lose slightly more weight than beef carcasses during conventional cooling is probably due to the greater area of exposed lean surface on bison carcasses, from which water is free to evaporate.  The distribution of finish on bison carcasses tends to be uneven and localized over the shoulder and loin (Hawley 1986 ; Koch et al. 1995 ) resulting in less protection from evaporation for underlying lean tissue as compared to beef carcasses with a more evenly distributed subcutaneous fat cover.  In our studies, total bison carcass saleable yield was 78%, similar to Hawley (1986)  who reported a mean saleable yield of approximately 77% from 6 bison steers 2.5 years of age at slaughter with an average liveweight of 444 kg.  Total saleable yield from the bison was greater than the sample population of beef (see accompanying table), an observation supported by Koch et al. (1995)  who reported similar findings upon carcass dissection comparison.  Koch et al. (1995)  also reported bison had less fat trim in all cuts except in the rib section, an area of localized subcutaneous fat deposition.

Also evident in our studies was the difference amongst relative weights of individual cuts when bison and beef were compared (see table).  The greatest disparity between bison and beef cuts appeared in the forequarter cuts, particularly the blade eye that, for bison carcasses, included the hump.  Due to the large dorsal spinous processes, bison carcasses had more meat in the shoulder region than beef (Koch et al. 1995 ).  Berg and Butterfield (1976)  reported similar observations, specifically the major difference between bison and beef carcasses was in the muscles connecting the neck to the forelimbs, including the hump.  The exaggerated size of the forequarter created the appearance of a disproportionately small hindquarter (Berg and Butterfield 1976 ; Koch et al. 1995 ), but there was a minimal difference between bison and beef hindquarter cuts.

^zCanada A1, A2, A3 beef data provided by W. Robertson, Lacombe Research Centre
^yIndex: Beef as reference=100; calculated as: (bison/beef) x 100

Meat Quality Traits

Throughout our studies, bison meat tended to have a similar range in shear force (objectively measured tenderness), darker meat colour, similar moisture and protein content, and lower intramuscular fat compared to beef.  A wide range of shear values was observed in our bison studies (4.00-18.47 kg).  Unless postmortem carcass treatment is appropriate for carcass type, variability of meat tenderness could become a consumer issue for bison meat similar to the situation with beef (Aalhus et al. 1992 ; Marriott and Claus 1994 ).  However, in a controlled comparison of bison and beef, Koch et al. (1995) reported bison meat had a lower mean shear force value and a greater taste panel acceptability rating for tenderness.

At the time of carcass grading (24 h postmortem) the bison meat in our studies was darker, more purple red, and had a greater colour intensity than the similarly evaluated beef samples described by Aalhus et al. (1992) .  Koch et al. (1995)  also reported darker Longissimus in bison than in beef.  By 6 d postmortem, the bison samples had become slightly brighter, and of a more intense purple-red colour than at 24 h.

Moisture content of bison LL was 74.9%, similar to values reported in the literature.  Marchello et al. (1989)  reported a 74.5% moisture content for bison, while Jeremiah et al. (1997)  quoted 73.6% for Canada A1 beef.  At 21.6% (WMB; wet matter basis), bison protein content in our studies was virtually identical to the 21.7% reported by Marchello et al. (1989) .  These workers also performed a simultaneous analysis of beef.  USA Choice grade beef, similar to Canada AA-AAA, contained 21.6% protein, not significantly different from bison, while crude fat content was 7.4%, significantly greater than the 1.9% reported for bison (Marchello et al. 1989 ).  Crude fat measured in our studies was 1.6%.

Challenges Facing the Beef Industry

Given the relatively minor differences between bison meat and beef, the bison industry will need to be flexible and creative to remain distinct from the beef industry.  In order to do this, the bison industry needs to learn from the three major challenges presently facing the North American beef industry: overfat carcasses, inconsistent quality and commodity based marketing.

Overfat Carcasses

In the 1980's, Canada’s beef grading system focused on the production of lean cattle by assigning the highest grade to cattle with 4-10 mm of backfat.  Canada's present day beef grading system, however, closely parallels the U.S. system that favours highly marbled carcasses (Prime) as their top grade.  As a result of focusing on marbling as a primary grade criteria, the #1 concern in the U.S. beef industry is production of overfat carcasses (National Cattlemen’s Association 1992 ).  In practical terms, the U.S. beef industry trims an average of 44.2 kg of fat from each carcass in order to satisfy a grading system which bases quality grades on marbling fat (Savell 1992 ).

To the bison producer, trimming these huge amounts of fat from a carcass probably seems unrealistic; however, there are some important take home points.  Firstly, the beef industry has focused on increased marbling as a means of ensuring consistent quality.  While consistent quality is extremely important, marbling accounts for only 10% of the variation in tenderness.  There are other, more effective, means of improving quality without producing overfat carcasses (see discussion below).  Secondly, this example demonstrates how the grading system can influence production practices.  In order to produce these types of overfat cattle, there are very few grass finished beef cattle in the system.

Hence, our words of caution to the bison industry.  The current bison grading system is very similar to the old beef cattle grading system, which has already caused some concerns since more mature, grass fed bison may be downgraded into C or D grades based on advanced ossification of the spinous processes.  While extremely advanced maturity (e.g. cull breeding stock) does have tenderness implications (due to increased collagen cross-linking), does the bison industry want the grading system to push production towards more youthful, and probably feedlot finished animals?  Or does the industry want to preserve the bison reputation for “natural, lean meat”?

Following the beef example in determining carcass grades may present other hazards to the bison industry.  Lack of finish, advanced maturity, yellow fat, low marbling and dark coloured meat are all discriminated against in the beef grading system.  Yet, do you want or need these characteristics discriminated against in the bison industry?  Certainly some of these characteristics go hand in hand with grass finishing (e.g. advanced maturity, yellow fat).  Based on the discussion by Price (1998) , the implementation of a branded product marketing system for bison would be an ideal method for avoiding certain limitations of a grading system, and for creatively marketing unique products of a guaranteed quality.

Consistency of Quality

In the early 1990’s, both U.S. and Canadian research flagged inconsistency in meat quality, particularly tenderness, as a major beef industry concern (Morgan et al. 1991 ; Aalhus et al. 1992 ).  A tremendous industry/research effort was sparked to attempt to produce beef carcasses of consistent tenderness.  In this regard, the beef industry could already have been thought more advanced than the bison industry since they currently market almost all animals after a feedlot-finishing period, while the carcasses are still rated as physiologically youthful.  However, even with a grading system that rewards increased marbling, the consumer would rate one in four steaks as unacceptable (Aalhus et al. 2000 ).  What could or should the beef industry do?  What can the bison industry learn?

Rather than controlling quality at the production end through genetics and nutritional management (a slow process with limited results), the opportune time is during the dynamic transition of muscle to meat.  Currently there are several known postmortem (after death) technologies that can improve tenderness in the carcass, particularly in the high value cuts.  We emphasize the high value cuts, because it is easy to forget carcass grading, and most determinations of meat quality, are typically only done on the Longissimus thoracis et lumborum (rib-eye/striploin muscle).  This muscle, representing about 7% of the carcass (Shahin et al. 1991), is contained in several of the highest value cuts and is most susceptible to quality defects in the eyes of the consumer due to its role as the barbecue king.  Two relatively simple postmortem technologies for improving tenderness in the loin muscle are electrical stimulation and altered carcass suspension  (aitch-bone suspension).

Electrical Stimulation

Almost all aspects of meat quality are affected by electrical stimulation including: tenderness, flavour, colour, heat ring, marbling, quality grade, retail case life, and processing properties.  In addition, electrical stimulation in the bleeding area can result in additional blood being forced from the carcass.  The magnitude of the effects, however, vary considerably depending on the type and method of electrical stimulation.  Low voltage electrical stimulation is applied in the bleeding area (via nose clamp) and accelerates the depletion of energy in the muscle, resulting in an earlier onset of rigor, before carcass temperatures have declined.  Using low voltage electrical stimulation, improvements to tenderness generally only result through prevention of cold toughening in rapidly chilled, lean carcasses.  On the other hand, high voltage electrical stimulation is usually applied later in the dressing process (via electrified probe), within an hour of exsanguination.  High voltage electrical stimulation improves tenderness as a result of both prevention of cold toughening and by physical damage to the tissues during the strenuous contractions.

In a Lacombe Research Centre (LRC) study designed to compare the efficacy of high (HVES), low (LVES) and combined high/low (HLES) voltage electrical stimulation, shear values were significantly lower in all the stimulated beef carcasses than in the control carcasses.  The difference in shear force ranged from a maximum of 1.3 kg between the HVES and control to a minimum of 0.86 kg between the LVES and CONT.  One kg of shear force is on the borderline for consumers to detect.  However, when a trained taste panel assessed the same samples, the panel showed a clear preference for steaks from high voltage stimulated carcasses (both HVES and HLES).  When scores for overall palatability were expressed as percent unacceptable, 77.8% of control and 76.3% of LVES steaks were rated as unacceptable, compared to 45.4% of HVES and 27.3% of HLES steaks.  Clearly high voltage stimulation can have a significant impact on improving tenderness.  However, effects of electrical stimulation, particularly with low voltage stimulation, are sometimes variable and can be affected by pre-slaughter handling (Butchers et al. 1998 ) and carcass fatness (Aalhus et al. 1994 ). 

Altered Carcass Suspension

Traditionally, beef carcass sides have been suspended by the Achilles tendon during postmortem chilling.  This method of carcass suspension allows considerable rigor shortening and results in a decrease in tenderness in some of the major muscles of the back and hindlimb in beef carcasses (Herring et al. 1965 ; Hostetler et al. 1972 ; Jeremiah et al. 1984 ).  Various methods of altered carcass suspension have been attempted (Hostetler et al. 1972 ; Fapohunda and Okubanjo 1987 ) and most reports indicate suspending carcasses by the aitch-bone (hip-free suspension) results in longer sarcomeres and improved tenderness in the loin and inside round muscles of the hindlimb.

While the beef industry has implemented electrical stimulation in many of the large plants, North American abattoirs do not use altered carcass suspension.  Altered suspension would require re-design of cooler space and grading lines in the beef industry since the carcasses typically are shorter and wider in an aitch bone hang configuration.  As well, the configuration of certain cuts of meat is altered, and the beef industry is resistant to changing the appearance of traditional beef cuts.  The proposed construction of new bison slaughter facilities which will operate at slower line speeds than the beef industry affords the opportunity to build in technologies to improve quality from the beginning.  As well, since consumers are not steeped in traditional conformation of bison cuts, retail cuts which are distinct in appearance from beef would probably be helpful to the industry.

Other Tenderness Enhancing Postmortem Carcass Technologies

In addition to electrical stimulation and aitch-bone suspension, quality improvements can be made using modified carcass chilling.  Elevated temperature conditioning in bison (10 h at 10 C) was shown to improve the degree and consistency of tenderness, and to accelerate tenderization during ageing (Janz et al. 2000 ).  Despite improving tenderness, the higher temperatures in the hip region resulted in bone sour in some carcasses.  At the opposite end of the temperature extreme, very fast chilling (VFC, achieving -1 C within 5 h postmortem) has been explored in beef carcasses (Aalhus et al. 1999 ) and is currently being investigated at the LRC for bison.  Generally, rapid chilling of beef carcasses is avoided to reduce the possibility of cold induced toughening, however, extreme chilling at –35 C for 10 h, resulted in a higher proportion of acceptable steaks than in control sides (83.3 vs. 33.3%, respectively).  At the present time the mechanism of action of VFC in terms of improving tenderness is unknown.  Clearly our understanding of the interaction between rate of cooling and meat quality limits our recommendation of the perfect chilling regime.  However, since chilling is the most expensive part of slaughtering and processing, the bison industry should carefully explore existing industry examples before committing to a chilling system.

Other innovative processing techniques to ensure consistent quality are also being developed.  The patented Hydrodyne process (patent numbers 5,273,766 and 5,328,403), passes shock waves through packaged meat suspended in water to elicit tenderization.  In a series of experiments using different sources of meat and different levels of explosive charge, Solomon and co-workers (1997)  have found improvements to shear force from as low as a 24% decrease in shear force for frozen meat to a high of a 72% decrease in shear force for fresh meat exposed to two independent 50 g loads of explosive.  Clearly, although an unorthodox treatment, hydrodyning can be very effective in improving tenderness, regardless of the muscle origin or type.  The mechanism of tenderization appears to lie in extreme disruption of the myofibrillar proteins (Zuckerman and Solomon 1998 ). A full-scale metal prototype unit, capable of handling 600 pounds of meat at a time has been constructed and is operational at a facility in Buena Vista, VA.  Should the hydrodyne procedure become a fully functional commercial entity, the benefits will include not only improved consistency in tenderness, but will also reduce or eliminate the need for extended periods of aging to ensure acceptable levels of tenderness.  The researchers are also investigating the possibility of utilizing hydrodyne to kill bacteria through rupture of the bacterial cell membranes.

As well, based on research by Koohmaraie and his co-workers (1988, 1989, 1991 ) showing infusion of carcasses with calcium chloride (calcium salt) accelerated postmortem tenderization, calcium activated tenderization (CAT) was developed for commercial use.  The final procedure developed for commercial application, consists of injecting post-rigor cuts of meat with 5% (by weight) of a 0.2 M solution of food-grade calcium chloride, followed by tumbling.  Published guidelines for the application of calcium chloride to enhance beef tenderness can be obtained from the National Live Stock and Meat Board (Item #11-415).  The recommended commercial procedure has been tested by consumers both in restaurants (Hoover et al. 1995 ) and at retail (Miller et al. 1995 ).  In the restaurant study, 90% of consumers rated CaCl₂ treated steaks acceptable compared to 73% of control steaks.  Despite all the developmental work for CAT, there is still skepticism towards beef industry adaptation and endangerment of the “fresh” meat status of beef.  However, in the pork industry, a division of Hormel Foods, Farmland Foods Inc. successfully markets “Extra Tender” pork products, produced by injecting 0.5% sodium phosphate on a 7% by weight basis into the meat.  Shear forces on these products are reduced by 25-30%, purportedly by increasing water holding capacity.  The product line is so successful, that once a store begins to market these products, they are unable to quit, because of consumer complaints about the toughness of “normal” pork.

Commodity based marketing

The beef industry has traditionally been a commodity based industry, relying on volume of sales to sustain prices.  The wake up call came in the late 1980’s when the beef industry continued to see its market share erode compared to the competition, chicken, and to a lesser extent pork.  Survey results clearly indicated consumers had concerns about consistency in quality and wanted convenient, value added products (McDonnell 1988 ).  The vast majority of consumers no longer had the time to figure out how to cook beef correctly.  The beef industry has responded admirably to the challenge of moving from a volume based industry to a quality based, value added industry; however, there is still room for growth.  With a new product, the bison industry has a unique opportunity to be a quality based, value-added industry from the beginning.  While a blueprint isn’t available, the best advice we can give is to think carefully about the status quo and consider innovative alternatives.

Instead of thinking of a carcass as a carcass, start thinking of a carcass as a collection of different marketable products.  Don’t think in traditional beef terms as steaks, roasts and hamburger.  Each muscle has its own unique properties based on its final pH, tenderness, water holding capacity, etc.  What is the best end use for each muscle?  Begin to treat muscles as different commodities on the carcass.  Should all muscles be chilled on average?  Can some muscles be used for further processing (e.g. jerky, sausage) and be hot-boned from the carcass?  This would capture energy efficiencies in not having to chill, and then re-heat the muscle during processing.  Can chilling be done to maximize quality in the high value cuts at the expense of the low value cuts?

How will the bison industry address seasonality of supply?  Beef consumers are reluctant to buy pre-frozen beef partly because the meat color is not a bright cherry red and because of misconceptions about the freshness or wholesomeness, yet frozen lamb is the norm.  Can the bison industry successfully market frozen product by capitalizing on the meat’s inherently darker purple-red color?  Or, like strawberries, will bison meat appear in the fresh food section once a year?

Perhaps the most important thing to know in setting up a quality-based, value-added industry is the consumer.  Who are/will be the bison consumer?  What do they want?  Do they want consumer friendly, value added products like Old West Bison Stew or Hickory Basted Bison Ribs?  Or do they want a fresh, bison steak for the summer barbecue?  Careful attention to the consumers of the new millennium will be a must for all successful meat industries.

Conclusion

The bison industry is a new meat industry with considerable future potential.  While the industry needs to learn from the challenges facing the beef industry, it is important to break free from the “brown, wooly cattle” way of thinking.  Although bison provide a protein source similar to beef, the secret to success will not be to adopt a slaughter and marketing system identical to the beef industry.  Be innovative, think creatively and keep bison unique, on the inside, as well as the outside.

Acknowledgements

Original bison data were collected thanks to the operational and technical staff at the Lacombe Research Centre.  Ongoing bison meat quality research at LRC is funded through the Peace Country Bison Association.

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