PORK AND PORK QUALITY PIH-127
PURDUE UNIVERSITY. COOPERATIVE EXTENSION SERVICE.
WEST LAFAYETTE, INDIANA
Pork Quality
Authors
Joseph G. Sebranek, Iowa State University
Max D. Judge, Purdue University
Reviewers
Larry Borchert, Madison, Wisconsin
Richard Epley, University of Minnesota
Robert Kauffman, University of Wisconsin
Roger Mandigo, University of Nebraska
Harold Hedrick, University of Missouri
``Pork Quality'' means one thing to the industry but may
mean quite another to consumers. Lean carcasses, high-yielding
cuts, attractive appearance, and stability in cold storage are
all characteristics that might be considered in the industry to
be some of the most important aspects of high-quality pork. The
ultimate objective of pork production is to provide food for peo-
ple, therefore, the industry must focus upon and understand the
definition of quality by consumers.
Consumer evaluation of pork quality occurs in the choice of
pork when purchased at the retail store or restaurant and in the
eating satisfaction experienced during consumption. Consequently,
consumer-perceived pork quality may be divided into two major
areas: those affecting appearance (and thereby selection) and
those affecting eating satisfaction (and thereby repeat sales).
Nutritional value and food safety are also becoming important
issues to consumers.
Appearance Characteristics
Lean muscle color helps establish consumer impressions of
quality. A bright reddish-pink is sought as an ideal; some varia-
tion of color is normal such as the different muscles of a ham.
However, muscle color changes quite easily, and as a result can
be indicative of meat quality. For example, as meat loses fresh-
ness and surface bacterial numbers increase, color may lighten
and fade to a gray tone. If dehydration occurs under poor packag-
ing conditions, color may also darken due to the concentration of
the pigment. These color changes thus indicate quality changes in
the product.
A more common color change results from the porcine stress
syndrome (PSS), where animals with genetic susceptibility to
stress react adversely to shipping and handling before slaughter.
Animals with severe PSS may die before slaughter. Those that sur-
vive transportation to a slaughter facility usually result in
very low quality pork with poor color. Meat from these surviving
animals is most frequently pale, soft and exudative (PSE). The
color is a very pale washed-out pink, which quickly turns gray or
even greenish-gray in retail display. These cuts will also be
soft and will lose excessive amounts of water from the muscle;
causing a watery exudate to form puddles on and around the cut in
a package. Obviously, the PSE condition results in an unattrac-
tive product for retailing and one which is lower in eating qual-
ity even though it is completely wholesome. Because of the water
losses (which are increased even more during cooking), PSE pork
results in a dry sensation when eaten and may seem tougher due to
the dryness. The PSE muscle also loses considerable weight due
to the water losses; consequently, yields are poor in processed
products such as ham. Other quality defects from PSE muscle in
processed products include excessive purge (free fluid) in pack-
aged products, poor slicing characteristics, mushy texture, and
uneven color distribution.
The PSS condition can also result in a dark muscle color
though it is less common than the pale color from PSE. This dark,
firm, and dry (DFD) product is just the opposite of PSE. However,
it can also be unattractive because the consumers may interpret
the dark red color as indicative of meat from an old animal, meat
that lacks freshness, or meat that has been dehydrated from
improper storage. The PSS pork carcass can, in some instances,
even result in a normal lean pork color.
The PSS-pork quality relationship has been recognized for
many years, but it has recently become critical as U.S. packers
attempt to compete in the world market. Buyers in the world
market, particularly the Japanese, are very quality conscious.
Therefore, PSE pork must be screened out of shipments from U.S.
packers to Japan. This results in a greater proportion of PSE
pork entering domestic markets. Because current information indi-
cates that about 15% of the carcasses in the industry may be PSE,
the amount of PSE pork on the domestic market could reach large
proportions (30% or more). This would have a strong adverse
effect on consumer perceptions of pork quality in the United
States. There is a wide range of reports on the actual incidence
of PSE carcasses observed. Some plants report 5% or less while
others complain of nearly 30% of the carcasses as PSE.
Controlling the PSE problem would be a major step forward in
the overall improvement of pork quality. Three solutions to this
problem exist. First, the problem is clearly genetic. Testing and
screening animals to eliminate the PSS tendencies from a herd is
possible and has been described in Pork Industry Handbook fact
sheet PIH-26, ``Porcine Stress Syndrome.'' Unfortunately, there
have not been any major economic incentives for pork producers to
do so. However, a major pork processing company recently
announced it will be measuring PSE levels and buying pork from
slaughter companies on the basis of quality. If this system is
extended to carcass evaluation for PSE and subsequently to pork
producers, there may be considerable incentive to determine and
eliminate the PSS. An important contribution to this solution is
accurate and rapid measurement of carcasses for PSE. Electronic
technology has been developed which offers good potential, but
none of the instruments developed so far has been completely
effective.
A second approach to reducing PSE is improved animal han-
dling to reduce stress before slaughter. Animals seem to be espe-
cially vulnerable to stress during climatic changes and fluctuat-
ing temperatures. In addition, a 2- to 3-hour rest after shipping
is effective. The thoughtful design of animal handling facilities
and careful animal handling procedures also reduce stress.
Third, carcass chilling rates need to be as rapid as possi-
ble because many slaughter facilities have found decreased
incidence of PSE by improved chilling. This includes decreasing
the time from slaughter to chill as well as increasing the chil-
ling efficiency. It should be noted that the PSE-quality problem
is not an ``either/or'' situation. The degree of quality loss
varies with the degree of PSE, which can range from slight to
extreme. Improvements in handling and chilling will not eliminate
quality losses but will lessen the degree and the incidence rate
of low-quality pork.
While muscle color serves as a reasonably good indicator of
PSS, it is not always an accurate indicator because color is not
the first quality characteristic lost as PSE develops. Rather,
water-binding losses occur first in the muscle during PSE
development, which means that pork can be watery without a dras-
tic color change.
The PSS-PSE problem is probably the best example of a rela-
tionship between visual appearance of pork and eating satisfac-
tion. There are other appearance characteristics that are impor-
tant to consumers. These include bone content, fat trim, and
intramuscular fat (marbling). Bone and external fat trim are con-
venience factors that influence edible meat yield. They have lit-
tle to do with eating enjoyment, however. Marbling, on the other
hand, contributes to juiciness and flavor of cooked products and
may improve tenderness slightly. Research indicates that a
minimum of about 4% of the muscle (small amounts of marbling in
quality standards) as intramuscular fat is necessary for a high
level of palatability of fresh pork cuts.
Product packaging plays an important role in product appear-
ance. Packaging may have little to do with inherent product
quality, but can have a great deal to do with retention of qual-
ity during storage. Packaging contributes significantly to the
visual impact needed in retail displays. An attractive package is
an important contributor to visual impressions of quality. How-
ever, consumers should be informed that the color of pork is
dependent on the type of packaging films utilized. Conventional
packaging allows passage of oxygen and produces a bright color.
Newer types of vacuum packaging which achieve a longer shelf
life, may result in a slightly different color (more purple as
opposed to pink). This color change is slight for pork and is, in
fact, probably insignificant unless the two packages were com-
pared side-by-side.
Factors Important to Eating
Satisfaction
Eating satisfaction occurs when a product is tender, has a
certain minimum juiciness and contains a pleasant, well-rounded
flavor. Water retention by meat during cooking is important to
these characteristics. Intramuscular fat content is important
because it contributes not only to juiciness but also to pork
flavor. The fat component in muscle can be modified by the type
of fat consumed by the pig. For example, fish meal and other oily
fat sources, if fed to pigs, have been shown to result in off-
flavored pork. Thus, fat flavor may influence the perceived
overall quality of pork flavor.
Fat is susceptible to change during storage of meat since
unsaturated fatty acids may develop rancid flavors. Cold tempera-
tures and good packaging are the best ways to reduce flavor
losses. However, even in frozen storage, pork will lose flavor
quality in a few months.
Preparation methods (cooking temperatures, oven types) can
greatly influence the eating quality of pork products. For exam-
ple, consumers usually overcook pork because of traditional
recommendations and fear of trichinosis. Trichinosis remains a
concern because about 110,000 infected hogs are slaughtered each
year. See Pork Industry Handbook fact sheet PIH-103, ``Trichi-
nosis.'' Cooking pork to a high internal temperature (such as the
often-recommended 185o F) to destroy trichinae results in a dry,
tough, unpalatable product. A lower internal temperature will
improve eating satisfaction. Trichinae larvae are destroyed at
137o F (see PIH-103), however, most cooking recommendations sug-
gest achieving an internal temperature of at least 160o F because
of uneven internal temperatures which develop during cooking.
Microwave cooking, however, is somewhat less lethal to the tri-
chinae organism, and 170o F (internal) has been recommended for
pork prepared in microwave ovens. It is also interesting to note
that cooking raw meat in the microwave does not result in palata-
bility characteristics identical to cooking in conventional
ovens. Microwave ovens are appropriate for reheating products
already cooked by conventional methods or for certain processed
meat such as weiners and bacon.
Nutritional Value
Historically, consumers have not had a good impression of
the nutritional quality of pork. Numerous studies have shown that
pork products have been viewed as high in fat and cholesterol,
difficult to digest, and low in relative value. Fortunately, in
recent years, leaner hogs and closer trimming have resulted in
much leaner cuts. It has been estimated that pigs are about 23%
leaner than those previously produced. See Pork Industry Handbook
fact sheet PIH-125, ``Composition and Nutritive Value of Pork.''
Thus, consumers may now perceive pork to be a lean meat.
Educational campaigns have begun to achieve significant
changes in consumer attitudes. For example, nutritionists have
been aware for some time of the high-quality protein, iron, and
B-vitamins supplied by pork products. For complete details on
nutritional value, see PIH-125. Reducing the fat content of pork
has diminished the consumer focus on fat in pork and has made the
positive nutritional qualities more obvious and more prominent.
Today, consumers should not consider closely trimmed pork to be
of low nutritional value. There has been a shift of consumer
perceptions away from ``fat pork'' toward ``lean, healthy pork.''
Safety
Food safety is an issue that has become increasingly prom-
inent. A safe food supply has been expected by consumers and
delivered by the industry for many years. However, an increasing
awareness of the potential for safety problems arising from
changes in production practices and processing techniques has
made consumers more determined that safety must be guaranteed.
Public confidence in the safety of pork consumption is high, but
a greater awareness of chemical, microbiological, and
drug/antibiotic problems has made public confidence very suscep-
tible to change. One news headline reporting an incident involv-
ing unsafe pork products could seriously damage consumer percep-
tions of pork quality and lead to decreased consumption and
demand.
Most of the safety concerns in the past have been centered
on pathogenic (food poisoning) microorganisms because meat pro-
vides a very good environment for microbiological growth. How-
ever, the food poisoning bacteria will not grow rapidly at refri-
gerated temperatures (below 40o F). In addition, spoilage bac-
teria in fresh meat which do not cause illness can grow in refri-
geration and will generally cause spoilage (off-odors, off-color)
before a product becomes unsafe. This means that on fresh meat
the spoilage bacteria usually change a product before the
illness-causing organisms reach large enough numbers to be harm-
ful. One of the pathogens often found on fresh meat, Salmonellae,
is easily killed by cooking and should not be a problem as long
as cooked products are kept separate from raw products. Conse-
quently, temperature control and good handling practices should
assure the safety of fresh pork from microbiological hazards.
Processed pork products elicit somewhat different safety
concerns because most of these products include either curing
agents (salt and nitrite) or have been heated for control of
spoilage. Because most spoilage bacteria are suppressed or killed
by heat, pathogens may have a chance to grow-particularly if
storage temperature is not well controlled. In these instances,
salt and nitrite in cured pork provide protection and insurance
against pathogens. One area of concern among microbiologists
involves the uncured, cooked, packaged meat products intended for
convenient microwave reheating. Many of these products have no
salt or nitrite and refrigerated temperature control becomes
extremely important to maintaining safety. The trends to reduced
salt content and less fat in processed meats also represent a
greater potential safety problem. These products have a higher
available water (Aw) and are more conducive to microbial growth.
Because consumers have been well educated to thoroughly cook
pork to eliminate trichinae, most pork is overcooked and less
palatable than it would be otherwise. An alternative for control
of trichinae is the irradiation processing of carcasses (recently
approved by the regulatory agencies). Low-dose irradiation will
control trichinae and permit use of lower cooking temperatures
for pork. Irradiation has been clearly shown to be safe, whole-
some, and effective but consumer attitudes toward irradiation
processing, while yet to be determined, appear to be largely
negative.
Safety concerns about chemical compounds used in pork pro-
ducts for processing and preservation, particularly sodium (from
salt), nitrite, and antioxidants such as BHA and BHT, have been
raised as issues. However, consumers should recognize that these
compounds control spoilage, inhibit pathogens, and contribute to
safety and overall quality. Recent research has better-defined
the appropriate use of these ingredients to achieve the best
compromise for safety and overall product quality. In most cases,
lower levels of the compounds are used in the industry than were
previously believed to be necessary.
While chemical and microbiological safety are determined
largely by the packer and processor, the more recent focus on
antibiotic and drug residues in meat is a primary responsibility
of producers. Antibiotic and drug residues represent a very legi-
timate and serious concern of consumers. There are good scien-
tific reasons for avoiding human consumption of these residues.
While they are effective for efficient production of market hogs,
it is crucial to the public trust that no significant residues
remain in pork at the retail market. The most serious residue
problem has involved sulfamethazine. However, all of the antibi-
otics and drugs used must be managed carefully to avoid residue
problems. See PIH-86, ``Management to Prevent Drug Residue Prob-
lems in Pork''. Pork containing antibiotic or drug residues
clearly diminishes the consumer concept of pork as a high-quality
food.
Summary
The term ``pork quality'' conveys different messages to dif-
ferent people. To pork processors, it relates primarily to func-
tional properties and color of the muscle. To retailers, it
relates to appearance of retail cuts, including fat and bone con-
tent, as well as color and juice loss or retention. To consumers,
any factor that affects pork eating satisfaction, safety, con-
venience, and nutritional value may fall within the definition of
pork quality. Pork producers must recognize all these require-
ments and use the management practices that maximize pork quality
for the entire industry. A sound breeding program that minimizes
problems like PSS, a careful feeding program to eliminate resi-
dues while producing lean pork, and well-controlled marketing
programs to avoid excessively fat hogs are all important com-
ponents of an overall effort to maximize quality.
NEW 12/90 (5M)
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