Agriculture Reference
In-Depth Information
impart a mouldy odour and taste if extensive and of
long standing. Moulds, too, may promote rancidity of
fat, and in doubtful cases, a portion of the meat should
be subjected to a boiling test after the meat has been
wiped or trimmed.
group. Black spot which is not too extensive and which is
unaccompanied by decomposition may be removed by
trimming. This is invariably practicable in quarters of
chilled beef, but in frozen mutton, the mould formation
may be so extensive on the inner aspect of the carcase,
neck and pelvic cavity that total condemnation is
required. Mould formation accompanied by bacterial
spoilage requires more generous paring and, at times,
condemnation of the whole quarter. It has been repeat-
edly borne out by practical experience that meat affected
with mould, and subsequently refrozen after trimming
or wiping, will develop mould more rapidly and in
greater abundance than meat which, though mouldy, has
not been so treated. Meat which has been trimmed or
wiped to remove mould therefore requires a quick sale.
Assessment of decomposition
The need has long been felt for a laboratory method to
establish the extent of spoilage in meat. To be of practical
value, such a test must be short and simple and must
provide unambiguous results which can be interpreted
with confidence. During the last 50-60 years, chemical,
bacteriological and physical tests have been developed
although none of these can substitute for organoleptic
inspection by an experienced inspector.
White spot
White spot is caused by
Sporotrichum
and
Chrysosporium
and is the most commonly encountered defect of
imported meat. It is seen as small, flat, woolly spots,
frequently accompanying black spot of similar size, but
it is whitish in colour and entirely superficial in nature.
The spores can develop at −8°C, grow more plentifully
at −2.5°C and become profuse when the temperature is
above 0°C.
Chemical tests
Various chemical methods have been suggested:
1
Tests based on the detection of free ammonia.
2
The determination of the total amount of volatile
bases produced during spoilage. In neither of these
cases does the test give a clear indication of spoilage
until the meat itself smells sufficiently to be con-
demned sensorially.
3
The determination of free amino acid content as an
indication of decomposition has been suggested, but it
is likewise unsuitable except as a guide to advanced
putrefaction.
4
The production of indole, sulphur and other volatile
products in decomposing meat has also been
investigated, but although in fish there seems to be a
relationship between spoilage and the amount of total
volatile reducing substances and total volatile acids
present, respectively, such a relationship has not been
established in meat.
5
Tests for meat spoilage based on either the oxygen
requirements of the meat or on its power of reduction
have been in existence for some time but have not
proved of practical value.
'Whiskers'
This fungoid growth belongs to the closely allied genera
Thamnidium and Mucor
. The hyphae grow well at 0°C
and may project more than 2.5 cm beyond the surface of
the meat, but they collapse in a relatively dry atmos-
phere. Though the growth of these moulds ceases at
temperatures below −7.5°C, they retain their viability
and proliferate if the temperature rises above freezing
point; thus, the presence of 'whiskers' indicates the meat
has been exposed during storage to a temperature at or
above 0°C.
Bluish-green moulds
Bluish-green moulds belong to the genus
Penicillium
and
are seen frequently on cheese, on unsound fruit and also
on meat. They are superficial in character and grow with
difficulty at 0°C, though conspicuous growths will occur
at a slightly higher temperature.
The superficial nature of white spot, 'whiskers' and
the bluish-green moulds renders their removal easy
by trimming. In imported forequarters of beef affected
with mould, particular attention should be paid to the
sawn surfaces of the vertebrae, especially the cervical
and first four or five dorsal vertebrae; all affected
bones should be removed (an affected pleura or peri-
toneum may be removed by stripping). In spite of the
non-pathogenic nature of most moulds, they may
Bacteriological test
Bacteriological methods have been devised to relate
bacterial plate counts to the quality of meat, but these do
not show any close relationship between the number of
bacteria present and the degree of spoilage as assessed
sensorially.
pH estimation
If the pH of deep muscle does not fall to 6.1 or below
within 24 hours, it is likely that the carcase will decom-
pose more rapidly than the norm.
