Meat (Pork) Quality / A Total Overview:

Practical Meat Quality Technology,

What Is Meat Quality?

Ronald Russell, Sr. Lecturer

Department of Animal Sciences

University of Wisconsin, Madison, WI


A very appropriate subject if indeed pork is to become the "Meat of Choice" by the millennium. Of course we need to bear in mind that pork is already the most consumed muscle food of animal origin on a global basis as we speak. Pork quality has been researched, described, cussed and discussed for well over fifty years, and we still find ourselves conducting conferences trying to figure out what it is as if it was a single entity in mere need of description and at which point the needs of all segments of the industry ranging from production through consumption would be met. The Pork Chain Quality Audit (1994) thoroughly reviewed the multiple factors involved in the evaluation of pork quality with the exception of bacteriological safety. The National Pork Producers Council (1997) hosted a conference earlier this summer under the banner "Quality Summit," again with little attention paid to food safety but with excellent and extensive reviews of the technologies of physical pork quality assessment and progress on the implementation of known technologies in industrial settings. I commend both to your review as excellent sources of material in the multiple facets of the "Quality" issue.

WHAT IS MEAT QUALITY?

Meat quality is a variable trait of which the definition depends on whose needs are to be met. The target is a consumer product which delivers safety/wholesomeness, and tenderness, juiciness and flavor (palatability traits). Greer (1988) and Kauffman et. al. (1969) defined meat quality as including a combination of traits that provide for a wholesome product that loses a minimum of constituents during handling, is free of spoilage and other abnormalities after processing and storage, is attractive in appearance, maintains a natural, healthful image, is convenient to prepare and appetizing, nutritious and palatable to eat. Kauffman et. al. (1990) suggests three levels of quality. The survival level demands that wholesomeness, as it affects safety and image, and nutrition as highlighted by proteins, vitamins and minerals, be maintained permanently in place. The economy level includes, in addition to wholesomeness and nutrition, minimum shrinkage during processing as affected by pH, and proper cooking conditions. Finally, the ideal level includes all characteristics of the survival and economy levels but insists on attractiveness, as controlled by color, convenience and consistency, and the ultimate in juiciness, tenderness, flavor and texture. Satisfying these levels requires five discussion categories of: wholesomeness, nutrition, shrink, appearance and palatability (tenderness, flavor and juiciness). Measures most often used in the assessment of the tissue are: pH, drip loss (water holding capacity), shear values, color (uniformity) and marbling. Wholesomeness (freedom from contamination), consistency, and nutrition are more akin to standards of identity and strongly influence consumer purchase decisions in ways difficult if not impossible to accurately measure.

Wholesomeness / safety

Not always thought of as a trait of meat quality, the safety from a food-borne illness potential perspective has become increasingly important. The pork industry cannot afford the bad publicity of food poisoning outbreaks. USDA needs to continue as a strong (reasonable) advocate pursuant with the objective of limiting the occurrence of cross-contamination. Keep in mind that, in the absence of infection or disease, muscle is essentially a sterile tissue until processors make it available to contamination. Abscesses (which are primarily of producer origin and often due to poor injection technique, equipment, etc.) are the leading cause of condemnation or trimming loss initiated during the postmortem inspection process (Cannon et. al., 1994). Healthy product originates from healthy animals. Contamination is the fourth leading cause of condemnation and the most common cause for necessitated trimming. HACCP must be at the forefront of processing procedures. What are the "critical control points" and how do we modify procedures? In the distribution of fresh product, contamination must be held to a minimum and handling (and storage) procedures must minimize the opportunity for the growth of pathogens and food spoilage organisms as well as minimizing deterioration such as oxidative rancidity. Products distributed as "fully cooked" must provide a kill step without opportunity for recontamination. Simultaneously, USDA needs to be reasonable (science based) in approaches to sanitation and recall procedures.

Nutrition

Nutrient contribution and eating enjoyment rank as dominant support factors for the inclusion of meat in the human diet. Lean muscle foods have long been recognized for their nutrient density. Again, healthy product comes from healthy animals. The avoidance of undesirable conditions like PSE, the product of which shrinks excessively before and during processing thereby losing water soluble nutrients, and excessive fat (more than 5% in fresh meats and more than 20% in processed) helps position muscle foods in a nutritious lifestyle.

Water-holding capacity

Arguably, the single most important factor in the evaluation of meat quality, the ability of muscle (meat) to retain its own or added moisture is related primarily to the factors of pH and protein denaturation. Postmortem pH decline and myofibrillar protein denaturation are thought to be responsible for the softness and accelerated drip loss of PSE meat (Forrest et. al. 1997). Forrest et. al. (1997) report that water in meat is primarily contained in the myofibrillar lattice and as the pHu drops near the isoeletric point (5.0 - 5.1) of myosin and actin, water-binding capacity is at a minimum. Therefore, higher pHu values result in greater net charges on muscle proteins and greater percentages of bound and immobilized water, keeping natural juices bound in the cells and reducing drip loss. The degree of denaturation of sarcoplasmic and myofibrillar proteins (attributed to low pH and high temperature during the early postmortem period) is believed to contribute to an increase in extracellular space and surface wateriness. Systems which minimize the rate and extent of postmortem pH decline will have a positive effect on the ultimate water - holding capacity of muscle. In addition to the genetic influence or susceptibility to stress (Porcine Stress Syndrome, RN gene, etc.), a remaining factor in the tendency for the development of PSE is that muscles that are high in the "Type II" fiber type, being more metabolically glycolytic, are more subject to the condition - a factor in both swine and poultry.

Appearance

Everything effects appearance in muscle foods ranging from age and abnormalities through composition, presentation, processing, and stress. PSE product is prone to early color deterioration in addition to purge or free exudate in packaging while DFD product which is considered off color because of its dark color is prone to more rapid microbiological deterioration because of its more neutral pH. The age of animals within a specie influences color attributed to myoglobin accumulation while species possess their inherent differences as well. Product appearance is largely a function of processing as well, including control of fat content in processed products, trimming and deboning level in fresh meats and the use of additives such as nitrite. Finally, the avoidance of abnormalities such as blood splash, steotosis and discolored fat is essential if muscle foods are to portray a positive image in the market. Packaging, presentation and marketing are very often among the most rewarded components in the market chain.

Palatability traits

Tenderness, flavor and juiciness, the traits most often used in the definition of ultimate quality are all difficult to objectively assess by virtue of the fact that the ultimate testing machine is a human. Humans are quite variable in their responses and given to error and inconsistencies, thus the dependency on tools like the Warner Bratzler Shear and Instron. Of course this isn't the only place that humans present problems in the determination of quality of muscle foods. Among the most common predictors of meat quality you won't find any that provide a greater correlation to final eating quality than 0.50. The statisticians among us will go on to explain that this means those very same predictors explain less than 25% of the variation in palatability. Method of preparation (Is it cooked right?) is the single greatest contributor to palatability. The challenge for processors is to provide a product which is complete in the other components of quality and which is easily prepared on a consistent basis.

Tenderness is the trait generally listed to be the dominant of the three palatability traits. Of the most consumed animal tissues, beef is the most highly variable. This tendency is largely explained by the degree of variation in the age of cattle (steers and heifers) at the time of slaughter which easily ranges from 12 to 26 months and beyond, combined with the variable post-slaughter (aging) time to consumption ranging from 5 to well beyond 30 days. Advancing animal age leads to greater connective tissue content and greater crosslinking of that tissue, while aging of the carcass or cut allows for proteolytic enzymes to degrade muscle proteins leading to increased tenderness. Tenderness in poultry and pork is less of a problem given the more consistent and youthful age at harvest. Here again the water holding capacity of the tissue is a major contributor to the tenderness profiles of products from all of the species.

Flavor and juiciness tend to parallel each other in most consumer tests. Generally, as juiciness goes, so does flavor perception. Again, as a function of water-holding capacity and processing, the ability of a product to retain its own or added moisture play a major role in the flavor / juiciness profile. Recognition is due with respect to the impact of specie on flavor but with increased leanness in a number of product offerings accompanied by spices and flavors, little of the flavor profile of many products has anything to do with the specie of origin. Does it matter?

PRACTICAL MEAT QUALITY TECHNOLOGY

Opportunities to modify meat quality parameters takes place at many points along the production chain leading from animal production all the way through to the final consumed product. Following is a partial review of a number of efforts and techniques that occur at the various stages of meat production. The list is not exhaustive but attempts to highlight and touch briefly on some of the more often used processes and some that appear promising.

Preslaughter handling

Efforts will continue to identify stress prone animals whether through halothane testing or via work on identification of the RN gene in various lines of swine which others in this conference are covering in its entirety. The influence of stress susceptibility (excitability) and ultimately less desirable meat quality is not limited to hogs and poultry. Voisinet, et. al. (1997) demonstrated a negative relationship between cattle temperament and beef quality traits of color and tenderness. Without doubt, animals (especially hogs and poultry) benefit from a rest period following shipping and prior to slaughter. In work by van der Wal, et. al. (1997) the length of resting period was negatively related with the temperatures of the m. longissimus and m. semimembranosis at 45 minutes postmortem, while the ultimate pH values, at longer periods of lairage, were significantly higher in combination with a darker color according to Hunter L* values and a color scale. Data supported the hypothesis that stress immediately prior to slaughter affects meat quality much more than stress experienced earlier on. In the same work the relationship between proper stunning of the live hog was associated with a decreased incidence of aberrant quality. Incorrect stunning procedures resulted in an increase in muscle activity during shackling and exsanguination, an earlier onset of rigor mortis, lower initial pH values and ultimately lower water-holding capacity in the product. A wide array of work has and is being done on the feeding of various compounds for the improvement of color (Work originally done at the University of Wisconsin, with vitamin E supplementation in cattle, has shown marked improvement in color stability resulting in increased shelf life for beef.), tenderness (Preliminary work with vitamin D by researchers at Colorado State has suggested improvements in beef tenderness.) and leanness (Researchers at the University of Wisconsin are in the early stages of work with conjugated linoleic acid - CLA - which is showing great promise in the improvement of carcass leanness in swine.). A number of other compounds, administered through either injectable or oral routes of administration, have been and are being researched generally with objectives of enhanced efficiency or rate of lean growth. Lean quality, in terms of tenderness, juiciness and flavor, are unfortunately often reduced in such scenarios.

Slaughter technologies

The primary technology which is applied during the slaughter process is that of electrical stimulation (ES). ES has been utilized very effectively in beef and lamb slaughter plants and the list of its benefits includes: enhanced lean color (thereby increasing Quality Grade), decreased incidence of cold shortening (resulting in increased tenderness) and increased blood yield at exsanguination. ES works primarily by accelerating the cascade of postmortem reactions in muscle including rapid pH decline. Thus, the fairly obvious reason that the same technology does not work well in the processing of pork.

In pursuit of increased wholesomeness / safety, slaughter technologies that have gained momentum in the beef industry are the use of steam pasteurization and organic acid spray washes for the purpose of beef carcass decontamination. Both technologies have been shown to decrease the levels of bacteria, including E. coli 0157:H7 and Salmonella species, but do not result in complete elimination.

Sort

Technology is rapidly advancing which provides for the sorting of products into known and established quality categories. The work by Morgan and Forrest (1997) shows great promise in the sorting of products by a color vision system. The result of which could be the separation of products which could be distributed "fresh" and those which could be distributed as "less expensive" or undergo "quality enhancement." Additionally sited is work with a tetrapolar impedance probe which shows promise of being able to predict ultimate meat quality as early as 36 minutes after slaughter. Currently available technologies are limited to sorting pork into the extremes, which still leaves the problem of exudative pork of normal color. Kauffman (1997) reported the ability to sort carcasses in to the quality categories of "desirable" and "undesirable." Why not take advantage of that ability and market the products accordingly? The beef industry has in place a system for the categorization of fresh beef into different "quality" groups via USDA, while pork in many systems of distribution is just "pork." In response to continuing concerns about the inconsistency of beef, Boleman, et. al. (1997) researched the tendencies of consumers to pay premiums for beef of guaranteed tenderness and found willingness to pay premiums approaching 10 to 20 %. In associated work, Shackelford and coworkers (1997) are developing a system for the early (24 hour postmortem) classification of beef according to tenderness class. The proposed system utilizes a Warner-Bratzler Shear to evaluate beef loin steaks at 1 or 2 days postmortem to predict tenderness following 14 days aging.

Processing treatments

The most commonly recognized "processing" techniques for the improvement of pork (and poultry) quality are the use of "rapid chilling" and moisture enhancement. Rapid chilling of the carcass has been shown to decrease the severity of the PSE condition, by slowing postmortem glycolysis rates, but not prevent it. However, carcasses (musculature) predisposed to extremes in PSE have already been exposed to the low pH / high temperature muscle conditions responsible for development of the condition. Moisture enhancement (injection with solutions of salt, sodium phosphate, etc.) has been used in the poultry (turkey) industry for many years and has more recently been effectively applied to "normal quality" pork products to provide products that excel in juiciness, flavor, and tenderness. The use of salt or sodium phosphate increases the water-holding capacity of meat so when injected in solution, provides the benefits of moisture and flavor (salt is an enhancer). The tenderness factor is accounted for via greater moisture retention, dilution of protein and the fact that water is tender.

More recently, work at the University of Wisconsin - Madison (Russell, et. al., 1997) has shown positive effects from the early identification of PSE pork and intervention treatments with sodium bicarbonate (baking soda) in a saline solution. The buffering capacity of the bicarbonate counteracts the rapid pH decline of the musculature resulting in a product that is elevated from PSE to normal or "ideal" quality. Combine this ability with early detection of PSE prone carcasses (Morgan and Forrest, 1997.) and the potential exists to greatly reduce the negative impacts of PSE. Flavor tended to be improved but not to the degree of statistical significance.

Finally, with respect to processing treatments that influence meat quality (wholesomeness), at the time of this writing, FDA announced approval of the use of irradiation of meat for pathogen control. Irradiation has been approved for use in poultry for some time. The use of this technology has the potential to greatly reduce the incidence of food-borne illness, but has to overcome the large obstacles of cost and consumer fear. At the same time, the ability to destroy E. coli 0157:H7 and Salmonella species in fresh meats without other deteriortative effects to the product is no substitute for sanitation during processing and preparation. Cross-contamination remains as a major source of bacteria which contribute to illness as well as spoilage.

Packaging

The primary purpose of packaging is maintenance of the product in as near its original condition as possible. Vacuum packages have the problem of visual purge which is of course exacerbated by poor water-holding capacity of the original product. However the protective role against oxidative rancidity is of great benefit. Work with the development of modified atmosphere packaging continues with the goal of finding the right combination of gasses to provide for color stability as well as protection against oxidation. Jeremiah and Gibson (1997 a,b) have demonstrated the usefulness of 100% CO2 atmospheres in the maintenance of color stability in pork loin roasts stored for extensive periods at sub-zero storage conditions (below 0 C, but above the freezing point of the tissue), while atmospheres of 70% O2 and 30% CO2 were the most effective in the avoidance of off-odor development. Composite results clearly emphasized the importance of sub-zero storage to the retail properties, and storage life of pork for all the types of storage atmospheres utilized. Both studies were conducted because for centralized processing and packaging of pork cuts to be effective, the chilled storage life of such cuts needs to be extended sufficiently to permit widespread distribution and merchandising.

Meat Quality?

The first criteria any perishable product must feature is that of safety. Food safety (hysteria) has become intrinsic to the consideration of nutrition sources, especially those of animal origin. Secondly, products must be palatable and preparable ("user friendly"). Palatability is a feature any product needs to sustain or improve consumption rates, while the ease of preparation has become an ever increasing criteria in food selection. Nutrition (defined in many consumer minds as a product which is not too fatty, but very subject to niche tendencies, while being considered an important source of protein) which has often been touted as a primary feature to stimulate consumption appears to be of lesser importance but still relevant. Features of "price/value," "brand loyalty," "source verified product," "organic," etc. are features around which consumers have a confidence, loyalty and/or trust based on knowledge, experience, or belief. Ultimately, a blend of all of the preceding come together in buying decisions with nearly as many different priorities as there are consumers.

Where do we go?

I commend to you reading the best selling book: The 7 Habits of Highly Effective People by Stephen R. Covey. While not being a read on meat quality, the principles contained within may be applied to personal management as well as organizations.

Habit 1: Be Proactive.

Think outside the box and don't let fear of the unknown keep you from looking into possibilities. Virtually every thing we do is by choice. Just do it!

Habit 2: Begin with the end in mind.

Define your objectives before just starting in helter skelter. What is the market? How can we adapt?

Habit 3: Put first things first.

Plan and organize. Determine your priorities and let the rest slide. If you're preoccupied with pleasing everyone or doing everything, you'll please no one and get nothing done. The main thing is to keep the main thing the main thing.

Habit 4: Think win-win.

The delivery of a "consumer preferred" product is win-win for the swine industry. Too often the adversarial relationship between producers/packer/retailers has contributed to a finger pointing blame game. Win-win or no deal.

Habit 5: Seek first to understand, then to be understood.

Listen. An industry that is preoccupied with "educating" the consumer is an industry in trouble. What do consumers want? Dollars spent out of the home for food have increased dramatically over the past decade and all indications are that in our growing economy, the trend will continue.

Habit 6: Synergize.

Capitalize on the strengths of diversity of abilities. Already evident in many segments of the industry at the producer level. Professionals (academics) are getting better, but are slow learners.

Habit 7: Sharpen the Saw.

Research must continue with emphasis on food quality with safety assurance. Read the literature. Regenerate. Learn from others -

The Wheel's Already Been Invented!

REFERENCES

Boleman, S.J., S.L. Boleman, R.K. Miller, J.F. Taylor, H.R. Cross, T.L. Wheeler, M. Koohmaraie, S.D. Shackelford, M.F. Miller, R.L. West, D.D. Johnson, and J.W. Savell. 1997. Consumer Evaluation of Beef of Known Categories of Tenderness. J. Anim. Sci. 75:1521-1534.

Cannon, J.E., J. Heavner, J.B. Morgan, F.K. McKeith and G.C. Smith. 1994. Pork Chain Quality Audit: A Review of the Factors Influencing Pork Quality. Manuscript No. JMF-21-94-1. NPPC. Des Moines.

Covey, S.R. 1989. The 7 Habits of Highly Effective People. Simon and Simon Pub. New York.

Forrest, J.C., E.B. Sheiss, M.P. Morgan and D.E. Gerrard. 1997. Pork Quality Measurement Tools - Now and In The Future, Proceedings NPPC Quality Summit, Des Moines, IA. July 7-8, 1997.

Greer, G.G. 1988. Bacteria and Meat Quality. Can. Inst. Food Sci. Technol. J. 22:116.

Jeremiah, L.E., and L.L. Gibson. 1997a. The Influence of Storage and Display Conditions on the Color Stability of Display-ready Pork Loin Roasts. Meat Science. Vol. 47, No. 1/2, 1-16.

Jeremiah, L.E., and L.L. Gibson. 1997b. The Influence of Storage and Display Conditions on the Retail Properties and Case-life of Display-ready Pork Loin Roasts. Meat Science. Vol. 47, No. 1/2, 17-27.

Kauffman, R.G. 1997. National Pork Quality Project, A Final Report to The National Pork Producers Council, Proceedings NPPC Quality Summit, Des Moines, IA. July 7-8, 1997.

Kauffman, R.G., W. Sybesma and G. Eikelenboom. 1990. In Search of Quality. J. Can. Inst. Food Sci. Technol. Vol. 23, No. 4/5.

Morgan, M.T., and J.C. Forrest. 1997. Color Vision System and Tetrapolar Electrodes for Assessing Pork Quality, Proceedings NPPC Quality Summit, Des Moines, IA. July 7-8, 1997.

Russell, R.L., R.G. Kauffman, M.L. Greaser, C.A. Cornelius, C.E. Suckow, and R. van Laack. 1997. Can PSE be Prevented by Injection of Sodium Bicarbonate into Pork? Abstract. ASAS/ADSA Meetings Midwest Section, Des Moines, Iowa. March 16-19.

Shackelford, S.D., T.L. Wheeler, and M. Koohmaraie. 1997. Tenderness Classification of Beef Longissimus Shear Force at 1 or 2 Days Postmortem as a Predictor of Aged Beef Tenderness. J. Anim. Sci. 75:2417-2422.

van der Wal, P.G., B. Engel and B. Hulsegge. 1997. Causes for Variation in Pork Quality. Meat Science. Vol. 46, No. 4, 319 - 327.

Voisinet, B.D., T. Grandin, S.F. O'Connor, J.D. Tatum and M.J. Deesing. 1997. Bos Indicus - Cross Feedlot Cattle with Excitable Temperaments have Tougher Meat and a Higher Incidence of Borderline Dark Cutters. Meat Science. Vol. 46, No. 4, 367 - 377.


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