Dealing with a persistent pink color in ground
beef
By Joseph Sebranek Ph.D
meatingplace.com, April 2008
"Persistent pinking" — a pink color that remains in uncured, cooked meat
products even after cooking at relatively high temperatures — is undesirable for
products where a thoroughly browned color is expected.
Persistent pink is a long-standing problem in the meat industry and occurs in
meat from all species. In the case of ground beef, however, it can be a
particular concern to consumers who are aware of the risk of Escherichia coli
O157:H7 in undercooked ground beef products.
Pinking of uncured, cooked meat can have several causes, and when it occurs, it
may be observed on both or either the exterior and interior of the product. The
most commonly recognized source of pinking is a small amount of cure (nitrate or
nitrite) contamination on an uncured product.
Even an extremely small amount of nitrite can produce a pink color in cooked
meat. Researchers have documented that as little as 14 parts per million nitrite
in beef is enough to result in pink color. The amounts are much less for pork
and poultry. Nitrate and nitrite contamination can occur from water sources,
contact with equipment surfaces previously used for cured meats and sometimes
non-meat ingredients such as protein concentrates. Eliminating this source of
pinking is simply a matter of determining the source of contamination by nitrite
or nitrate.
A second source of persistent pink can be the gases produced during cooking.
This is particularly true for gas ovens, where the gas flame can produce a
mixture of carbon monoxide and nitrogen oxides. It has long been thought that
this source of pinking was caused by either carbon monoxide or nitric oxide in
the oven gases, but researchers have found that nitrogen dioxide in oven gases
is a much more potent pinking agent. This gas will produce pink color in beef at
a concentration as low as 2.5 parts per million.
Nitrogen dioxide is a highly effective pinking agent because it is absorbed
readily into the water phase on the meat surface and combines with water to form
nitrous acid and nitric oxide. The nitric oxide then reacts with meat pigment to
produce cured meat color.
Pinking in this case is typically a surface color change because of the limited
penetration of the gas. Using gas burners with low nitrogen oxide emissions can
eliminate the surface pinking; however, with many whole muscle products, such as
smoked or barbecued products, surface pinking is considered desirable, because
the sliced product then displays a pink ring around the outside of the slice.
Another gas that can result in pink color of cooked meat is ammonia. Exposure of
fresh meat to ammonia, perhaps during a refrigeration leak, may result in
pinking when the product is cooked.
The third possible cause of pinking in uncured, cooked meat is muscle
biochemistry. A considerable amount of research has demonstrated that meat
pigment becomes increasingly heat stable as pH increases. This is especially
true in the presence of reducing compounds, some of which are inherently present
in muscle. Because a reducing environment is facilitated by oxygen removal, the
interior of a high pH meat product, where oxygen is very low or absent, is much
more conducive to persistent pinking. This product will resemble an undercooked
product because the surface is likely to be brown while the interior remains
pink.
The role of oxygen is also why this form of pinking is more likely to occur in
vacuum environments, such as those that exist with packaged products or canned
products. It is possible to observe pinking in cooked products under vacuum that
have been heat sterilized with a cooking temperature over 212 degrees F.
This pinking problem becomes most prevalent with dark-cutting beef, which
results from cattle that, due to environmental conditions (weather,
temperature), diet or stress, have relatively low muscle energy stores when
harvested. While normal post-mortem beef muscle will have a pH of about 5.7,
dark-cutting beef has a final muscle pH over 6.0 and, because of the dark color,
may be used primarily for ground beef. The result is a ground beef product that
can retain an interior pink color even after cooking to 160 degrees F. It has
been reported that a cooked temperature as high as 190 degrees F may be
necessary to eliminate pink color in ground beef with a pinking problem. In this
case, the excessive cooking temperature is likely to severely reduce cooked
product palatability.
Pinking that is induced by muscle biochemistry is difficult to control. The
addition of acids, oxidizing compounds and brown coloring agents has been shown
to reduce or eliminate ground beef pinking, but each brings disadvantages of its
own in terms of flavor and color changes. The best approach is to try to
eliminate the causes of high muscle pH in the beef sources used.
A fourth possible cause of persistent pinking is carbon monoxide as a result of
modified atmosphere packaging that uses CO. Carbon monoxide forms a very stable
bond with meat pigment and provides a highly stable color for fresh meat in this
packaging environment. Several research reports have indicated that the carbon
monoxide pigment also retains greater stability during cooking, and products
packaged in this environment are likely to retain greater pink color following
cooking.
Division Maryland Hotel Supply Co., Inc.