PORK AND PORK QUALITY                             PIH-127


                         Pork Quality

Joseph G. Sebranek, Iowa State University
Max D. Judge, Purdue University

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

     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

     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.''


     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

     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

     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


     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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