Agriculture Reference
In-Depth Information
The synovial fluid of the hip joint is also a favourable
medium for bacterial growth with a pH between 7.0 and
8.0, whereas that of muscle in complete rigour is usually
below 6.0. The lymph stream may also be important, for
bacteria resembling those in taints have been isolated
more frequently from lymph nodes than from bone mar-
row and muscle. These bacteria may therefore be present
in the lymph nodes during life and, under suitable condi-
tions, may spread to the surrounding muscular tissue.
The odour of bone taint is apparent in both the muscula-
ture around the femur and in the bone marrow; it is very
typical, quite unlike that of decomposing meat and
resembles the sewage-like smell associated with gut-
cleaning. The condition may be associated with a change
in the muscle colouration to a grey or at times a blackish
purple, but frequently, the normal red colouration is
entirely preserved.
Bone taint in cattle
can be reduced by avoiding
bacterial contamination of the carcase with rapid cool-
ing to 1.5°C. Experimentally, tetracycline injections
immediately before slaughter and antibiotic spraying
of the carcase can prevent taint. The smaller butcher
can aid the dissipation of heat from the freshly killed
carcase of beef by removing the fat from the kidney
and the pelvic cavity. Incision of the stifle joint, to
promote air access and rapid cooling, will prevent the
growth of anaerobic bacteria. To avoid bone taint, the
temperature at the centre of the round must not exceed
4.5°C after 48 hours. Bone taint is a local condition
requiring condemnation of the affected tissues, but in
many cases, when the hip joint or round of beef is
affected, generous trimming of the muscle around the
femur is all that is necessary.
rancid odour may be detected if a piece of fat is rubbed
between the hands. Chemical methods of assessing
rancidity include the measuring of peroxides produced
utilising potassium iodide. The thiobarbituric acid
(TBA) test and the Kreis test both rely on the intensity of
a colour change to indicate the degree of rancidity which
has developed.
Microbial-associated rancidification, a further factor
causing taint in fat, is the activity of micro-organisms
which produce hydrolysis, resulting in the liberation of
free fatty acids. Experiments show that the fat of the kid-
ney, brisket and back of the ox develops a taint when the
free fatty acids reach 2.5-3.0%. The deep intramuscular
fat of meat, as is seen in the marbling of prime beef, is not
affected by hydrolysis or atmospheric oxidation and is
therefore likely to remain sound for long periods, but the
kidney and abdominal fat, being more exposed, is likely
to develop rancidity early; it is for this reason that these
superficial fats are removed by the retail butcher before
the carcase is hung up in the shop. Fats should be
regarded with suspicion if they contain over 2% of free
fatty acids, although in practice the appearance, odour
and flavour are the usual guidelines.
Bone taint
The rapid dissipation of body heat from a freshly killed
carcase is facilitated when the surrounding air is cool,
dry and in rapid circulation. The rate of cooling is slow
in heavy carcases owing to their greater thickness and
also in those which carry an excessive amount of fat,
with the result that a high temperature may persist in
the deep-seated musculature of these animals and give
rise to deleterious change. This change, known as
bone
taint
, is associated with the growth of putrefactive bac-
teria and occurs most commonly in the region of the
hip
joint of the ox and pig
, but occasionally in the
shoulder
region of the ox
, especially when ambient temperatures
are high. The condition, which was commonly encoun-
tered in the days when there was inadequate refrigera-
tion and during the warm summer months, is not a
serious problem today.
Bone taint, or deep-seated spoilage of meat, is undoubt-
edly of bacterial origin. More than one organism may be
involved, but the
anaerobic spore-forming bacteria
are the
most important and probably emanate from the gut of
the animal. It appears likely that the organisms enter the
bloodstream before death, rather than during it or at the
bleeding stage, and that this entrance is facilitated by pre-
slaughter exhaustion, fright, shock or a sudden strain, for
example, the ascent to the top floor of the factory, which
predisposes the tissues around the head of the femur to
bone taint. There is practical evidence that putrefaction
can commence in the blood vessels of the bone marrow.
Taint in hams
Taint in hams is also known as
souring
and is attributed
by American authorities to contamination by
Cl. sporo-
genes
,
Cl. pufrefaciens
and
Cl. putrificum
, which are pro-
teolytic organisms and break down proteins into amino
acids and ammonia. The taints in hams and beef are fun-
damentally similar in origin, being in each case a deep
form of decomposition which is un-associated with any
surface change. Though the blood, marrow, muscle and
bone of normal live pigs are free from ham-souring bacte-
ria, these micro-organisms may be present in such tissues
soon after slaughter and develop rapidly along con-
nective tissue bands between the muscle bundles. The
sticking knife undoubtedly contributes bacteria to the
bloodstream, which can be demonstrated experimen-
tally by placing pure cultures of
uncommon
bacteria on
the knife blade and isolating them from the tibia and
other long bones. The marrow of the femur tends to har-
bour fewer bacteria than the tibia, and as American
