Agriculture Reference
In-Depth Information
in not more than one of five 25 g samples. The ICMSF
also recommended that
frozen poultry
when examined
by rinsing should give a count at 20°C of less than 10
7
/ml
of the rinsing solution and that
Salmonella
should be
detected in not more than one of five 25 g samples of
the poultry meat.
The Commission of the European Union Code of
Good Hygiene Practices gives indications on the micro-
biological checks on the general hygiene of conditions
of production in establishments producing fresh meat,
giving specifications on the nature of these controls,
their frequency as well as the sampling methods and the
methods for bacteriological examination (also www.
ukmeat.org). These checks form part of the validation
and verification of the mandatory food safety manage-
ment system, which will incorporate the principle of the
hazard analysis and critical control points (HACCP),
which the operator must put in place and implement.
The monitoring of the safety management system may
be used to assess the nature and degree of bacterial con-
tamination on walls, floors, equipment and fittings and
the hands and clothing of personnel. Tests at various
operational stages, for example, at the beginning and end
of work and after cleansing procedures, should provide
criteria which can be reasonably maintained under eve-
ryday conditions. The results should be interpreted care-
fully, and allowance made for factors such as the time of
year, time of day, type of stock being handled, cleanliness
of animals, staff quality, etc.
While microbial counts form the basis of food micro-
biological criterion, they have limitations and should be
interpreted with care for the following reasons:
teria, moulds and yeasts, reducing the meat into a
number of simpler chemical substances, many of which
are gaseous and foul smelling. All forms of foods in their
natural state remain in a fresh and edible state for only a
comparatively short time. Foods are rapidly colonised by
bacteria, moulds or yeasts, which are the main causes of
spoilage, a consequence of decomposition by factors
such as enzyme action and oxidation.
Enzymes
, present in all living cells, catalyse the com-
plicated chemical reactions taking place in the cells. The
process of
autolysis
- self-destruction or self-degradation -
is essentially brought about by enzymes and at a rate
which varies markedly in the different tissues. In general,
it is highest in those tissues in which protein is syn-
thesised in large amounts and which have high water
contents, for example, gastrointestinal mucosa, testes,
pancreas and adrenals. The
water contents
of some types
of meat and offal are given in Table 12.2. Tissues such as
the liver, kidneys and endocrine glands have slower
autolytic rates, and the tissues with the lowest metabolic
rates such as the skin, muscles, bone, heart and blood
vessels have the lowest autolytic rates of all.
All forms of food are subject to natural deterioration,
their shelf life being dependent on their structure, pH,
composition, water content, presence or absence of
bacteria and/or damage and conditions of storage. It is
accepted that meat from fatigued animals spoils faster.
The pH of the meat from these animals, on the comple-
tion of rigor mortis, is in the region of 6.5 rather than the
lower normal value in a rested animal of around 5.6.
Such a low pH (pH 5.6) slows the growth of bacteria, as
this is outside their optimal pH range, thus slowing down
the functioning of the enzyme systems and the transport
of nutrients into the microbial cells.
Bacteria, moulds and yeasts are affected by factors
such as temperature, moisture, availability of oxygen,
nutrients and the presence or absence of growth inhibi-
tors. Control of one or more of these factors inhibits
microbial growth and lengthens the shelf life. In addition
to microbial spoilage, physical damage which occurs
1
Bacteria in food are not stable like heavy metals; their
populations change constantly. Different strains of
bacteria vary in toxin and allergen production and in
invasiveness.
2
Food usually contains a variety of micro-organisms,
some or all of which may enhance or inhibit each other.
3
Time of sampling, usually at plant or retail shop, gives
no indication of the final microbial count in the con-
sumer's home, long after sale.
4
The number of organisms or amount of toxin or aller-
gen which affects man is not known.
5
Environmental conditions, for example, temperature,
pH and type of sampling, markedly influence bacterial
growth.
Table 12.2
Water content of meat and offal
Water in grams/100 g of meat
Liver, ox, raw
73.3
Chicken breast, raw
73.7
Beef steak, raw
68.3
Chicken, boiled
61.0
Part 3: Meat decomposition and spoilage
Decomposition is the process by which organic matter is
broken down into a simpler form, primarily in meat pro-
tein but also fats and carbohydrates, by the action of bac-
Beef, corned, canned
58.5
Bacon, Danish, tank-cured
46.9
Bacon, English, dry-cured
36.3
Meat, dehydrated
7.5
