Agriculture Reference
In-Depth Information
absence of accompanying gas-forming bacteria, there
will be no 'blow' and the can will appear normal. Most
cases of food poisoning now associated with canned
foods are the result of contamination after the can is
opened, but a number of cases of typhoid fever associ-
ated with canned foods have occurred in Britain. The
outbreak in Aberdeen in 1964, in which there were over
400 confirmed cases, was attributed to the post-process-
ing entry of contaminated cooling water in a 2.7 kg tin of
corned beef of South American origin.
Viewing the question as a whole, canned foods are con-
siderably less likely to be a source of food poisoning than
ordinary fresh foods. The possibility of secondary con-
tamination of canned foods with pathogenic bacteria also
raises the question of the wisdom of leaving food in a can
after it has been opened. From the public health stand-
point, there is no reason why an open can, properly stored,
should not be used as a food container; it should, however,
be covered to prevent contamination and kept cool.
the first few months. Where unfilled cans are stored and
allowed to rust internally before being filled, the can
edges may become rusted, with the result that during
processing a chemical action may take place between the
rust and meat juices and give rise to an unsightly grey
precipitate of iron phosphate in the meat jelly.
Considerable significance should be attached to cans
damaged
by rough handling, the important factor in
their judgement being the extent and location of the
damage. Marked deformation of the can seam is attended
by considerable risk of leakage, and such cans should be
condemned. Slight indentations on the can body are per-
missible, but severe dents on the body may cause seam
distortion, and such cans should be rejected; any can
having a dent at one end should also be rejected for it is
possible to reduce a springer to normal, at any rate tem-
porarily, by hitting it upon the corner of a box. Nail holes
in cans caused during the closing of packing cases may
also be encountered, and such cans should be rejected
even if the contained foodstuff appears perfectly normal.
It is important to reject any can which is in the least sus-
picious or which shows lack of concavity of the ends.
Microbiological examination of canned meats
Where suspected outbreaks of food poisoning attributed
to canned food occur, the normal laboratory procedures
for isolation of the responsible organism (
Salmonella,
Staphylococcus, Clostridium
, etc.) are adopted, care being
taken in the sampling, transport, identification, han-
dling, etc. of the suspect food.
In order to ensure the safety and stability of large con-
signments of hermetically sealed containers of meat prod-
ucts, attention should be directed at the standards of
methods used at the point of production
(quality assur-
ance), namely, hygiene levels, temperatures for heat treat-
ment, water supply, etc., which should supply more
important information than the microbiological testing of
numerous containers, which would not only be wasteful
but would be unlikely to detect entities such as botulism.
Examination of the
quality of containers
is impor-
tant to ensure that there are no damaged, rusty, blown,
etc. cans. If there is reason to suspect that a consign-
ment of meat products in hermetically sealed contain-
ers is unsatisfactory, sampling and inspection
procedures should be adopted along the lines recom-
mended by the Codex Alimentarius Commission (see
'Further reading'). The number of samples to be taken
is assessed according to the expected hazard and the
laboratory facilities available in the case of shelf-stable
canned products. For non-shelf-stable products, five
containers are examined visually and their contents
examined microbiologically. Both
aerobic
and
anaero-
bic
microbiological techniques are undertaken, deci-
sions as to rejection or approval being based on
bacterial plate counts (Sampling and Inspection
Procedures for Microbiological Examination of Meat
The public health aspect of canned foods
Improvements in the canning industry during recent
years, together with greater appreciation of its hygienic
requirements, have done much to remove the public prej-
udice against canned foods, which were thought to cause
food poisoning. Food poisoning is usually the result of
improper handling of food during preparation or storage,
and with the exception of botulism, food-poisoning out-
breaks are nearly always caused by bacteria which would
be destroyed during processing.
Salmonellae
are destroyed
with certainty by the temperatures attained in commer-
cial processing. The minimum standard of processing
now universally recognised by reputable canners ensures
the destruction of
Cl. botulinum
spores in low- and
medium-acid foods. A lower processing temperature is,
however, permissible in cases such as cured meats, in
which the curing salts have an inhibitory effect on the
growth of the organism and the production of toxin.
Staphylococci, and more rarely streptococci, are now
recognised as a cause of food poisoning mainly in pre-
pared or unheated foods, such as cheese, salad, milk or
ice cream. These organisms are ubiquitous in nature, but
their main source is the human or animal body, where
they are normally present on the skin, in the intestine
and in the respiratory tract. Staphylococci, however, are
relatively susceptible to heat, and even the more resistant
staphylococcal enterotoxin, which may withstand a tem-
perature of 100°C for 30 minutes, is destroyed during
commercial processing. Cans may occasionally become
infected by these organisms through a leak, and in the
