e. Texture Changes. The following texture changes are associated with
microbial spoilage: surface slime, stickiness, whiskers (fuzzy growth), spongy texture,
surface growth, swelling (of vacuum-packed meats), and cloudiness.
f. Tasting the Product. If microbial spoilage is suspected, DO NOT TASTE
THE PRODUCT. The veterinary officer should be contacted for further examination of
the product.
g. Growth of Microorganisms. Since fresh animal products are perishable,
they are chilled and stored in ice or a refrigerator at 0 to 4C (32 to 39F). This means
that psychrophilic organisms (organisms capable of growing at refrigeration
temperatures) become dominant. Microorganisms are the primary cause of spoilage in
meat and meat products. Spoilage of meat is due to the growth and metabolism of
large numbers of microorganisms on the surface or the interior. Most spoilage is on the
surface. The number of organisms that are present when spoilage is evident varies
from 106 to 108 per cm2 of meat surface. This variation apparently is due to the activity
of the organisms present, as well as the criteria used by the investigators to determine
spoilage.
h. Spoilage Organisms. The temperature of the meat is perhaps the most
important factor that determines the predominant microflora and the resultant spoilage.
At temperatures of 50C (122F) or higher, thermophilic bacteria can grow. Usually
these bacteria cause spoilage of heat-processed meats that have been improperly
handled during processing. Intermediate temperatures (15 to 30C) (59 to 86F) may
occur when the chilling of meat is slow, delayed, or the meat is held in this temperature
range. In these cases, the main spoilage organisms are the mesophilic clostridia. They
cause internal spoilage or bone taint in beef. At low temperatures (0C, 32F),
spoilage is evidenced on the surface. Under storage conditions which foster a moist
meat surface, spoilage is due to gram-negative bacteria, especially Pseudomonas
species.
i. Water as a Factor. The water activity of the product can play a role in
microbial spoilage. Water activity (aw) is defined as the ratio of the water vapor
pressure of the food substance to the vapor pressure of pure water at the same
temperature. This is an index of the availability of water for chemical reactions and
microbial growth. At an aw of 0.96 or less, most of the usual microorganisms causing
spoilage of fresh meat are inhibited. When the surface of meat has an aw lower than
0.96, the slower-growing fungi become evident. The conditions seen will be "whiskers"
caused by Thamnidium, black spot caused by Cladosporium, and white spot caused by
Sporotrichum. Generally, the activity of molds is limited to the outer surface of meat
where aerobic conditions prevail.
MD0723
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