CLEANING AND DISINFECTION IN FOOD ESTABLISHMENTS
The operations of cleaning and disinfection are essential parts of food
production and the efficiency with which these operations are performed
greatly affects final product quality.
1. Cleaning
The surfaces of the equipment used in the manufacture of foods inevitably
become soiled and require cleaning. If not continuous, cleaning must at least
be performed at regular and frequent intervals so that a consistently good
quality of product is maintained. How this cleaning is done depends principally
on:
 the nature of the soil or contamination to be removed;
 the type of surface to be cleaned;
 the materials used for cleaning;
 the degree of water hardness; and
 the standard of cleanliness required.
The basic steps in cleaning can be summarized as:
 the removal of gross soil or dirt;
 the removal of any residual soil with detergent; and
 rinsing to remove detergent and soil.
The first step is omitted where continuous cleaning or CIP systems are
installed. But cleaning often needs to be followed by disinfection (sanitizing) or
sterilization which involves two further steps, viz. the disinfection or sterilization
of surfaces with suitable agents to destroy microorganisms and the rinsing off
of these agents.
1.1.
Types and removal of soil
The type of soil to be removed varies according to the composition of the food
and the nature of the process to which the food has been subjected. However,
the food constituents themselves vary markedly in terms of their cleanability
2
(Table 1) so that a wide choice of cleaning materials must be available for their
removal.
Table 1
Soil characteristics
Component
Solubility
Ease of
on surface
Change on heating
removal
Sugar
water soluble
easy
caramelization;
more difficult to clean
Fat
water insoluble, alkali soluble
difficult
polymerization;
more difficult to clean
Protein
water
insoluble,
alkali
very difficult
soluble, slightly acid soluble
denaturation;
much more difficult to
clean
Mineral salts water solubility varies;
variable
generally insignificant
most are acid soluble
Food residues may be dry particulate, dried-on, cooked-on, sticky, fatty or
slimy. Such residues may be best removed by physical means or by the use of
hot or cold water supplemented with detergents. The length of time of food
residue is left undisturbed also affects the ease of cleaning. For example, fresh
raw milk can be readily washed away but if it is allowed to dry greater difficulty
will be experienced. This is due to the denaturation of the milk protein and the
breakdown of the fat emulsion which results in the fat spreading over other
milk particles making them more difficult to remove.
Since the main function of a detergent is to facilitate soil removal, any
preliminary conventional cleaning might be unnecessary. However, if the bulk
of the debris can be removed in a preliminary cleaning process a much
reduced and more accurately assessable amount of detergent can be used to
remove the residual soil; therefore this latter approach is recommended where
feasible and it should be initiated as soon as possible after processing has
stopped.
3
The preliminary cleaning of smaller equipment may involve presoaking in
warm or cold water to remove loosely adhering debris. The more tenacious
food debris can then be brushed or scraped off by hand in warm water (c.
45oC). Brush bristles should be as hard as possible but should not cause
damage to the surfaces to be cleaned. Any cleaning aid causing damage to
stainless steel or other food contact surfaces must be avoided since crevices
can be formed which are more likely to retain bacteria. The sole use of high
pressure water jets for cleaning is usually inadequate; only gross dirt is
removed and even that can be ineffective especially when machines are
poorly designed.
1.2. Detergents
1.2.1. Required properties
Detergents must be capable of removing many different types of soil under a
variety of conditions; the list of properties required for a good detergent is
therefore an extensive one. Thus, ideally, detergents should be:

readily soluble in water at the desired temperature;

non-corrosive to equipment surfaces;

non-toxic, non-irritating;

odourless;

biodegradable;

economical in use;

readily rinsable;

effective cleaners of all types of soil.
In general, detergents are not expected to possess bactericidal properties
although in practice some of them do. However, detergents do physically
remove a large number of bacteria during cleaning and this makes subsequent
disinfection that much easier.
1.2.2. Classification and main compounds
Inorganic alkalis. Many detergents incorporate an alkali as one of the
principal ingredients. Sodium hydroxide (caustic soda) is the strongest of the
alkalis and cheap. It has excellent dissolving properties, is a very strong
4
saponifier and has added advantage of being strongly bactericidal. It is,
however, highly corrosive to metals especially aluminium and extreme care
must be taken when handling this detergent as it can cause severe burns to
the skin; for this reason protective clothing must be worn together with goggles
and rubber gloves when working with this detergent. As with all the alkali
detergents sodium hydroxide precipitates insoluble calcium and magnesium
salts from hard water so that sequestering agents need to be incorporated with
alkali cleaners in any detergent formulation. Sodium metasilicate, although a
strong alkali, is non-caustic and therefore much less corrosive than sodium
hydroxide. It supresses the corrosive activity of sodium hydroxide and the two
are often combined in detergents for this reason. Sodium carbonate (soda
ash) is a relatively weak detergent, is somewhat corrosive and precipitates
calcium and magnesium salts from hard water. However, it is cheap and has a
good buffering capacity (i.e. stabilizes pH) and is frequently included in
detergents for this reason. Trisodium phosphate (TSP) is a good emulsifier
and saponifier has strong dispersive properties and has the ability to soften
water by precipitating the salts. Although again somewhat corrosive, it is often
incorporated in detergents.
Inorganic and organic acids. Acids are not widely used in the food industry
as they are usually corrosive, and many are dangerous and can cause severe
skin burns so that protective clothing must be worn. Of the inorganics,
hydrochloric, sulphuric and nitric acids have been used in the past by the dairy
industry to remove hard water scale and other mineral deposits (e.g.
“milkstone”, a deposit of protein, calcium carbonate and other salts which
builds up in pasteurizers when milk films are not completely removed) but, due
to the extremely corrosive nature of these acids, they have been largely
replaced by milder acids. Amongst these are phosphoric and sulphamic acids
which are less corrosive and, when coupled with a corrosion inhibitor, can be
very effective. However, low levels of stronger acids may be used where
deposit build up is excessive.
5
Organic acids, which are bacteriostatic in action, are much milder than the
inorganic acids and are therefore safer to handle. Amongst the organic acids
which have been incorporated in detergent formulations we can find gluconic,
hydroxyacetic, citric and tartaric acid. Acid detergents usually incorporate
corrosion inhibitors and wetting agents and as such can be employed in the
removal of inorganic deposits and milkstone, and in bottle washing.
Surface active agents. Surface active agents reduce the surface tension of
water to facilitate wetting. The classical surface active agent is soap which is
usually composed of sodium or potassium salts of fatty acids such as stearic,
palmitic and oleic acids. Soaps are reasonably effective in soft water but their
reduced solubility in cold water constituents a disadvantage; in addition, soaps
form precipitates with calcium in hard water to give insoluble deposits. For
these reasons they have been largely replaced by synthetic detergents which
are either anionic, cationic, non-ionic or amphoteric depending on their active
electrical charge when in solution. When negative charges predominate the
surfactant is classed as anionic, when positive cationic, whilst surfactants that
do not dissociate in solution are termed non-ionic. Where the predominant
charge varies according to pH the surfactant is then termed amphoteric.
Surface active agents have a molecular structure comprising a hydrophilic and
a hydrophobic portion. One end of the molecule is thus attracted by water and
the other end is repelled but is attracted by fat and oil and this is the basis of
the cleaning action of surfactants. There are many hundreds of surface active
agents now available which are incorporated into detergent formulations.
Surfactants are usually excellent emulsifying agents, they have good wetting
and penetrating powers, they are non-corrosive, non-irritating and readily
rinsable. In addition, they are highly soluble in cold water, are largely
unaffected by hard water and many are stable in both acid and alkaline
conditions. Whilst the bactericidal activity of both the anionic and non-ionic
detergents is poor, that of some cationics is excellent although the latter are
less good as detergents. For this reason the cationic surfactants are used as
disinfectants and sterilizers (and are discussed later in this chapter). Many
6
surfactants produce high amounts of foam especially where considerable
turbulence is generated during cleaning. To control the extent of foaming, antifoaming agents are often incorporated in formulations. The principal anionic
surfactants used today are alkyl sulphates or alkylbenzene sulphonates. The
hydrophobic portions of the molecules are represented by the alkyl (i.e. lauryl)
and benzene groups whilst the hydrophilic portions are represented by
sulphate and sulphonate; the cations are commonly sodium or potassium. All
anionic surfactants are high foam producers and none can be combined with a
cationic detergent.
The non-ionic surfactants are not dissociated in solution and can be used in
conjunction with either anionic or cationic agents. They are powerful
emulsifying agents, are unaffected by hard water and vary considerably in their
foaming characteristics. As with the anionic agents, the list of non-ionic
surfactants is an extensive one. Two of the major categories are based on
products formed by condensation reactions between ethylene oxide and
synthetic long chain alcohols (e.g. lauryl alcohol ethoxylate) or between
ethylene oxide and alkyl phenols (e.g. nonyl phenol ethoxylate). The former
represent the major group of low foaming surfactants in many countries.
Amphoteric surfactants can exist in solution in either the cationic or anionic
form depending on the pH. They are based on amino acids and have the
general formula R-NH-CH2-COOH where R is usually an alkyl radical. An
example is dodecyl diaminoethyl glycine. The amphoteric agents are relatively
good emulsifiers, are stable in both acids and alkalis and show a good
tolerance to hard water.
Sequestering agents are added to detergents to prevent calcium and
magnesium salts although in the long term it is often far cheaper to soften a
hard water supply than to add high concentrations of sequestrants to
detergents. Obviously the amount of sequestrants that is added depends on
the extent of water hardness and the overall detergent formulation. Of the
inorganic sequestering agents, sodium polyphosphates are widely used. They
are also good emulsifiers, dissolving and dispersing agents and also generally
7
enhance rinsability. The principal organic sequestering agents, also called
chelating agents, are ethylene diamine tetraacetic acid (EDTA) and its sodium
and potassium salts, and the sodium salts of gluconic and heptonic acid. In
spite of their relative expense they are fairly widely used, because of their high
solubility in liquid detergent formulations.
Modern detergent formulations are carefully blended mixtures of different
chemicals each contributing to the desired properties of the detergent. A
general-purpose cleaner may contain alkali builders to break up grease,
surfactants to improve wetting, dispersion and rinsability, and sequestrants to
stabilize magnesium and calcium; the level of the sequestrants should be
carefully adjusted depending on the degree of water hardness and in-use
concentration. Sodium metasilicate may also be added as a cleaning agent
with the added benefit of being a corrosion inhibitor especially if susceptible
metals such as aluminium are to be cleaned.
When disinfecting food contact surfaces of equipment and pipework it is rarely
necessary to achieve absolute sterility. The usual aim is to so reduce the
numbers of microorganisms that those remaining (i.e. some bacterial spores
and possibly a few highly resistant vegetative cells) could not affect the
microbiological quality of the food coming into contact with these surfaces.
Either heat or chemicals can be used for plant disinfections operations but it is
important to stress that these operations must be preceded by thorough
cleaning. The efficiency of chemical disinfectants is undermined by the
presence of soil and the cleaner the surface the more effective will be the
disinfectant. Disinfection should follow immediately after cleaning although it is
often advisable, if not essential, to disinfect surfaces a second time
immediately before a process run if the equipment has been left unused for a
lengthy period.
8
2.1. Chemical disinfectants
2.1.1. Desirable properties
Disinfectants for use on food contact surfaces should ideally have the following
properties:
 Capable of rapidly killing microorganisms and, in particular, equally
effective against both Gram-positive and Gram-negative bacteria. The
majority of mould spores should be killed and the destruction of bacterial
spores would be an added advantage.
 Reasonably stable in the presence of organic residues and, if
necessary, effective in the presence of hard water salts.
 Non-toxic and non-irritating to the skin and eyes.
 Non-corrosive and non-staining to plant surfaces of whatever type.
 Odourless or have an inoffensive odour.
 Readily soluble in water and readily rinsable.
 Competitively priced and cost-effective in use.
2.1.2. Classification and main compounds used in food industry
Chlorine-releasing compounds. The hypochlorites are the most widely used
for all disinfectants in the food industry but there are a number of other
chlorine-releasing compounds which are also used on a more limited scale.
Amongst the latter are gaseous chlorine and chlorinated trisodium phosphate
as well as the organic chloramines, derivatives of isocyanuric acid and
dichlorodimethylhydantoin.
In general, chlorine-releasing compounds are powerful disinfectants with a
broad spectrum of activity, Gram-positive and Gram-negative bacteria being
equally susceptible; furthermore, these compounds show some activity against
bacterial spores. Many chlorine-releasing compounds are inexpensive; all are
easy to use and unaffected by hard water. However, it is essential to maintain
a high pH to prevent corrosion effects even though, as a consequence, some
loss of bactericidal activity is experienced. Perhaps the main disadvantage of
chlorine-releasing agents is that they are rapidly inactivated by the presence of
9
organic matter although an additional weakness is that they must be carefully
rinsed off to prevent corrosion.
Of the hypochlorites, hypochlorous acid (HOCl) itself is unstable but many of
its salts can be prepared and these are invariably more stable. In solution
these salts dissociate to form OCl- which is the ion that is responsible for the
bactericidal properties of the hypochlorites. The most widely used salt is
sodium hypochlorite (NaOCl) which is available in commercial form as a
concentrated liquid containing c. 10-14%, available chlorine. Also used is
calcium hypochlorite (Ca(OCl)2) which is available in powdered form and
contains c. 30% available chlorine. Hypochlorite solutions should always be
stored in dark containers; stability is also improved if chill storage is employed.
Solutions are more stable above pH 9.5 whereas germicidal activity is maximal
between pH 4 and pH 5; at the letter pH corrosion effects are also maximal.
Because of these corrosion problems, solutions of pH 10-11 are used and
operating temperatures are kept relatively low since at higher temperatures
corrosivity and loss of stability of the disinfectant occur. In-use concentrations
typically vary between 50 and 200 ppm available chlorine and contact times of
between 3 and 30 min are normal; it should be remembered that in each
situation the minimum concentration and time to effect the necessary kill-off
should be employed in order to avoid possible corrosion of susceptible
surfaces.
Chlorine gas is commonly used for the disinfection of water supplies but is also
has some application in the food industry. Where employed it must be fed into
the water supply at a constant rate by means of a chlorinator. It is necessary to
chlorinate above the “break point” of water, that is the level at which the
chlorine demand of the water, a variable factor depending primarily on the
amounts of suspended solids and organic matter, has been satisfied. In fact
chloramines (see later) are formed if ammonia-releasing compounds are
present in the water and at higher chlorine doses these are oxidized. Only
after this is the “break point” reached so that thereafter any additional chlorine
10
creates a residuum of free chlorine. A residual chlorine level of between 1 and
5 ppm is suitable for most continuous plant chlorination systems.
The chloramines, e.g. chloramine T, chloramine B and dichloramine T are
much more stable than the hypochlorites in the presence of organic matter,
they are less irritating and toxic but their expense has undoubtedly limited their
use. Furthermore, in spite of an available chlorine content of 25-30%, they are
weaker bactericides except at high pH values (>10) where they are more
active than the hypochlorites. Chloramines release chlorine slowly and are
often used where equipment and utensils can be soaked for long periods since
they are only weakly corrosive; rinsing after their application is necessary,
however. They are often combined with alkali detergents to from detergentsterilizers.
Iodophors. These compounds consist of soluble mixtures of iodine with a
surfactant (typically non-ionic, although anionic and cationic surfactants may
be used) which acts as a carrier for the iodine; it is the iodine which imparts
the bactericidal activity. Iodophors can thus also be regarded as detergentsterilizers although the detergency power depends on the amount of surfactant
in the mixture. Since iodofors are most active in the pH range of 3-5, usually
also an acidic component, mostly phosphoric acids is added to the mixture in
order to lower the pH of the solution (phosphoric acid buffers in the required
range). Iodophors effect the rapid killing of a broad spectrum of bacteria and
resemble hypochlorites in this respects but they also maintain a reasonable
activity in the presence of organic wastes provided in the pH is not above 4
and the quantity of waste is not excessive; iodophors are, however, much less
active against spores than hypochlorites.
Iodophors are rather expensive and, in consequence, are not used widely;
they are essentially non-corrosive, non-irritating, non-toxic and have little smell
but they must be thoroughly rinsed off after use. Some plastic materials may
absorb the iodine and become discoloured when exposed to these
compounds; rubber also tends to absorb the iodine so that long contact times
with the iodophor are to be avoided to prevent possible tainting of foods.
11
Iodophors are unsuitable for cleaning equipment used for processing starchcontaining foods since iodine forms a purple complex with starch. One
advantage of the iodophors is that they are unaffected by hard water salts;
they are also stable in concentrated form although over long periods of storage
at high ambient temperatures some loss of activity is possible.
Iodophors are used mainly in dairies where, in addition to their bactericidal
powers, the phosphoric acid is useful in the control of milkstone; iodophors are
also used in the brewing industry. Operating temperatures of up to 45-50oC
can be employed with iodine concentrations varying between 10 and 100 ppm.
Quaternary ammonium compounds. Quaternary ammonium compounds,
known as “quaternaries”, “quats” or “QACs”, are essentially ammonium salts
with some or all of the hydrogen atoms in the (NH4)+ ion substituted by alkyl or
aryl groups; the anion is usually a chloride or bromide. The general formula is
thus:
R2
R1
N
+
R3
X-
R4
where R1, R2, R3 and R4 represent one or more alkyl or aryl groups substituting
for hydrogen and X- represents a halide, either Cl- or Br-. The large cation is
the active part of the molecule whilst the anion is important only in that it can
affect the solubility of the QAC. The QACs are very active bactericides against
Gram-positive bacteria but are less effective against Gram-negative forms
unless sequestrants are present; bacterial spores are relatively resistant. After
disinfection surfaces treated with QACs retain a bacteriostatic film due to the
adsorption of the disinfectant on the surface; this film prevents the subsequent
growth of residual bacteria. When required, rinsability can be improved by
adding a small quantity of a non-ionic surfactant to the disinfectant. QACs
retain their activity over a relatively wide pH range although they are most
12
active in slightly alkaline conditions and activity falls off rapidly below pH 5. In
comparison with the hypochlorites the QACs are more expensive but they
have many desirable properties. Thus Qacs are largely unaffected by the
presence of organic debris, they are non-corrosive, although some types of
rubber may be adversely affected, and they are non-irritating to the skin,
except at high concentrations, so they can be handled with reasonable safety.
Since QACs are cationic surfactants they also have some detergent activities
but they cannot be used in conjuction with anionic surfactants or even with
certain non-ionic surfactants. Hard water salts reduce the activity of QACs.
However, care must be taken with the selection of the sequestrant employed
since some are incompatibel with some QACs and cause their precipitation.
Strong alkalis induce a similar effect and cannot be used with many Qacs; in
general, detergents containing such materials must be carefully rinsed off
before the QAC is added. QACs often foam vigorosuly in solution so they are
generally unsuitable for CIP systems (see later). They are used at
concentrations of between 50 and 500 ppm, at temperatures in excess of 40 oC
and with contact times varying between 1 and 30 min.
Amphoteric compounds. Whilst some of the amphoteric surfactants are
primilary detergents with weak bactericidal powers there are others, the
imidazoline derivatives, which are relatively stronger bactericides and weaker
detergents; an example is ethyl -oxypropionic imidazole. Amphoterics can
exist as cations or anions depending on the pH of the solution and it is in the
cationic state that these compounds are bactericidally active. They are
generally more expensive than other disinfectants and are not particularly
effective bactericides although they can be blended with Qacs to improve their
efficiency. Amphoteric disinfectants are not markedly affected by organic
matter or by water hardness, they are non-corrosive, non-toxic and odourless,
and they are stable, even in dilute form, for lengthy periods. However, they do
tend to foam and, becasue of their expense and limited activity, amphoteric
dsinfectants have not been widely used in the food industry.
13
Phenolic compounds. Many phenolic compounds have strong bactericidal
powers and they are widely used as general-purpose disinfectants. Phenolics
are, however, not used in disinfecting operations on food plant because of
their strong odours and because of the possibility of transmitting off-flavours to
foods.
Detergent-disinfectants. Detergent-disinfectants or also known as detergentsanitizers, are essentially combinations of compatible and complementary
ingredients; they contain a detergent and a separate disinfectant, so that
cleaning and disinfection can be performed in a single operation. Many of the
aforementioned ingredients have been used in combination; widely used
groupings are given in Table 2.
Table 2
Commonly used detergent-disinfectant combinations
Detergent
Inorganic alkalis
Disinfectant
+
Hypochlorites
Organic chlorine-releasing compounds
QACs
Inorganic acids
+
Non-ionic surfactants
Iodophors
Anion surfactants
+
Organic chlorine-releasing compounds
Non-ionic surfactants
+
QACs
Iodophors
In practice, the detergent-disinfectant formulations are likely to contain other
components such as sequestering agenst and buffers, and two surfactants are
often included in a single formulation provided they are compatible.
2.2. Use of heat
Heat alone can also be used to disinfect food plant and it can be supplied in
the form of steam, hot water or hot air. Heat in the form of pressurized steam
is the most effective method of sterilization; moist heat kills microorganisms at
14
relatively low temperatures by denaturation of the protein but proteins are far
more stable in dry conditions so that far higher temperatures and/or longer
times are necessary to effect a kill using hot air. Thus, whenever possible,
moist forms of heat are used to sterilize equipment but obviously the efficiency
is also dependent on the temperature and time employed. Moist heat is a
favoured disinfecting or sterilizing agent because it is non-corrosive,
economical, has excellent penetration powers, leaves no residue and is active
against the large majority of microorganisms.
Steam. Saturated steam is a good disinfecting agent and has the potential to
destroy all but the most heat-resistant bacterial spores. However, it is essential
that heat is applied to surfaces, both internal and external, long enough to heat
them to a temperature of c. 85oC for 1 min; under these conditions all but
bacterial spores should be killed. Unfortunately steam guns are frequently
misused and the short-term blowing of steam against equipment may do more
harm than good by supplying warmth and moisure to bacteria enabling them to
thrive, especially in the presence of food debris. It is very important that steam
per se is not a cleaning agent and it should thereore only be used to treat
clean surfaces.
Hot water. It can be used to disinfect food plant at 80-90oC. It is used at these
temperatures in cleaning-in-place (CIP) systems where it usually acts as a
detergent carrier rather than as the disinfecting agent; contact times of 5-15
min are desirable when it is used in the latetr capacity. Small items of
equipment can be disinfected by immersing them in water which is heated to
about 80oC for 10 min when all but bacterial spores should be killed.
3. Cleaning-in-place (CIP)
CIP has largely replaced manual clenaing for equipment used for process
liquid foods, i.e. in the dairy, brewing and soft drinks industries. The form CIP
takes can vary considerably from the cleaning of individual items of equipment
to sophisticated operations involving whole processing lines. The cleaning
principle is similar in all cases and involves the sequential circulation of water,
15
detergents and disinfectants through pipelines and processing equipment
which remain assembled. The basic sequence of operations is:
 a pre-rinse with cold water to remove gross soil;
 the circulation of detergent to remove residual soil;
 an intermediate cold water rinse to flush out detergent;
 the circulation of disinfectant to kill any residual microorganisms;
 a final cold water rinse to flush out disinfectant.
This can be varied, for example, by the use of detergent-sterilizers to replace
certain stages. Apart from the chemical effects of the detergents and
disinfectants, the mechanical force generated by the flow of fluids through
pipes or from spray heads assists in the removal of soil from food contact
surfaces; in the case of pipes a velocity of c. 1.5 m/s is required to obtain the
desired turbulence. CIP is commonly used for pipelines, tanks, vats, heat
exchangers and homogenizers but other food processing equipment can be
suitably designed to enable CIP systems to be introduced.
4. Assessment of cleaning and disinfection efficiency
The efficiancy of process line sanitation can be checked by visual inspection or
by using microbiological techniques. Visual inspection is a simple but rough
method which cannot determine the microbiological cleanliness achieved.
Much depends on the care taken by the inspector. With experience the
inspector may know where to look for signs of inadequate cleaning but
residual soils vary in their visual detectability (e.g. some soils are not visible if
there is a film of water on the cleaned surface) and high intensity lighting must
be directed on surfaces during inspection. These inspections can be carried
out during or immediately after cleaning or even shortly before the start of the
next production run. A check-list of various items of equipment should be
prepared and items, once cleaned and inspected, can be given a cleanliness
rating which can be compared with earlier data. All the findings should be
recorded in an inspection report. Additionally, records of the cleaning
materials, dilutions and application times used should be kept. If equipment
has not been adequately cleaned there should be time available for corrective
16
action before processing is restarted; particular care should be taken with the
subsequent inspection of equipment given low cleanliness ratings.
The
most
commonly
used
tests
are
by
ATP-bioluminescence
and
microbiological culturing. The ATP-bioluminescence test determines the
hygienic status since it is not specific for microbial ATP but will detect ATP
form residual food material as well. Microbiological culturing typically involves
estimations from surface areas of the total numbers of viable bacteria,
indicator organisms (i.e. coliforms, E. coli, etc.) and, where warranted, specific
food spoilage, or food poisoning bacteria (i.e. Listeria). In general, however,
estaminations are limited to “total numbers” as this is the most sensitive guide
to microbial hygienic status. The bacteria are removed from surfaces by
means of sterile swabs, by rinsing with a known volume of sterile diluent or by
agar contact method. The inherent problem with standard microbiological
methods is that test results are normally unavailable until after 48 h period due
to the need for incubation of the test samples. Hence the ATPbioluminescence method has found considerable favour in the food industry
mainly because the results are obtained rapidly.