a. General. Examine the product for discoloration/darkening.

b. Sources of Discoloration. Discoloration/darkening may be due to hydrolysis reactions, surface evaporation, or microbial spoilage.

c. Other Sources. The inspector may find other deteriorative conditions such as dehydration or microbial spoilage in determining discoloration in meat and meat products.

d. Surface Discolorations. The following surface discolorations may be observed in meat and meat products.

(1) Browning. A brownish discoloration on the cut or outside surface of ham or sausage is often associated with dehydration. The cured meat pigment is chemically altered to metmyoglobin under storage conditions. Low humidity, especially at storage temperatures considered to be too high for the product, may result in a rather rapid browning of cured meat products. A packaging film which is less permeable to water and oxygen will retard the onset of this type of discoloration. Browning of the lean areas of bacon is commonly observed. In addition to dehydration, the discoloration is sometimes traced to the presence of excessive nitrite. A high nitrite content will tend to oxidize the pigment in the cut lean surfaces to metmyoglobin.

(2) Fading due to undercure. Fading may be an indication of insufficient nitrite in the cure. Consequently, a low residual nitrite level will result in a weak cured color. This type of discoloration is often observed on the cut surfaces of hams or in such products as frankfurters. Under such conditions, the interior color is pale pink, which tends to fade rapidly upon exposure to oxygen.

(3) Greening due to overcure. Nitrite burn, which is due to an excess of nitrite in the cure, is often observed in acid-cured meat products such as the fermented sausages and pickled pigs' feet. In fermented sausages, it may arise from excessive nitrite reduction by bacteria during the fermentation process. Nitrite burn in pickled pigs' feet usually produces a browning of the muscle tissues and an undesirable greening of the skin and other collagenous tissues. Even the vinegar pickle may acquire a greenish tint.

(4) Fading from rancid fats. Fats with a high organic peroxide content are sometimes incorporated into sausages. This may result in instability of the surface color. Such fats may also impair the flavor of the product. Attempts to store frankfurters for prolonged periods of time in the frozen state often result in rancidity development and surface fading.

(5) Chemical fading. Although the cured meat pigment is heat stable, it is very susceptible to oxidation. Any oxidizing chemical applied to the cured meat surface may result in a discoloration. For example, very dilute solutions of hydrogen peroxide will cause a fading or greening of the cured meat surface. Overzealous use of hypochlorites as sanitizing agents can result in difficulties if any of the chemical reaches the surface of cured meats.

(6) Bacterial greening. Surface discoloration of sausages and other cured meats caused by bacteria is common.

(a) The bacteria are deposited in the surfaces during the usual handling procedures following heat processing. If suitable environmental conditions are provided, these bacteria grow rapidly on the surface and discolor the cured meat pigment through hydrogen peroxide accumulation.

(b) Several kinds of bacteria are capable of producing a greenish discoloration of meat pigment. They include the following genera: Lactobacillus, Leuconostoc, and Pediococcus.

(c) Bacterial greening of meat surfaces is a direct reflection of malpractice in sanitation and/or holding conditions of the finished product. Contamination occurs usually as the result of direct contact with equipment, employees, or another product harboring the microorganisms.

(d) Following contamination, if the product is held in an environment that maintains a moist surface and a suitable growing temperature, the discoloration becomes apparent. Discoloration is usually accompanied by a slimy surface, caused by heavy bacterial growth.

e. Interior Discolorations. The following interior discolorations may be observed in meat and meat products.

(1) Overcure or undercure.

(a) An excess of nitrite, especially in the fermented sausages, may result in a greenish core, which is apparent at the time of cutting the sausage. Green cores may also accompany surface greening from nitrite burn.

(b) Conversely, insufficient nitrite may result in a faded interior of a cured meat. This condition is seen in hams and sometimes results from a rupture of the vascular system at the time of pumping the ham with curing pickle. In this event, there may be a portion of the ham which never receives a sufficient quantity of the curing agents.

(2) Green rings and cores.

(a) Green rings in sausages are known to be of bacterial origin, although the exact mechanism of their formation is unknown. The rings appear at varying depths beneath the surface, usually 2 to 4 mm, and may be of varying thicknesses. They are apparent at the time of cutting and tend to fade within a few hours.

(b) Green cores of bacterial origin occur rather commonly, especially among the larger sausages. The discolored core is not apparent at the time of cutting but becomes visible within one to several hours after exposure to the air. In several cases, the discoloration may show through to the surface. A common microorganism associated with sausage green cores is Lactobacillus viridescens. This bacterium has an extreme thermal tolerance (very heat-resistant).

(c) Another similar internal greening problem occasionally encountered is the discoloration of canned hams. At the time of opening, the tissues appear normal. However, when they are sliced and packaged for display purposes, the color may fade or turn green rapidly. Streptococcus faecium is often found to be the responsible microorganism in such instances. This bacterium is relatively heat-resistant and is able to grow at refrigeration temperatures. This organism survives the thermal processing during canning of the ham and grows rapidly prior to the time of opening. There is no swelling of the can and it may have no off-flavors or off-odors, with the exception of an occasional sour flavor.

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