14.1 Introduction
Chapter 13 has outlined the concept of ‘hygienic design’ and ‘hygienic
practices’ in controlling the safety of chilled food products. This chapter deals
with hygienic practices, specifically those related to cleaning and disinfection.
Contamination in food products may arise from four main sources: the
constituent raw materials, surfaces, people (and other animals) and the air.
Control of the raw materials is addressed elsewhere in this book and is the only
non-environmental contamination route. Food may pick up contamination as it is
moved across product contact surfaces or if it is touched or comes into contact
with people (food handlers) or other animals (pests). The air acts as both a source
of contamination, i.e. from outside the processing area, or as a transport medium,
e.g. moving contamination from non-product to product contact surfaces.
Provided that the process environment and production equipment have been
hygienically designed (Chapter 13), cleaning and disinfection (referred to
together as ‘sanitation’) are the major day-to-day controls of the environmental
routes of food product contamination. When undertaken correctly, sanitation
programmes have been shown to be cost-effective and easy to manage, and, if
diligently applied, can reduce the risk of microbial or foreign body
contamination. Given the intrinsic demand for high standards of hygiene in
the production of short shelf-life chilled foods, together with pressure from
customers, consumers and legislation for ever-increasing hygiene standards,
sanitation demands the same degree of attention as any other key process in the
manufacture of safe and wholesome chilled foods.
This chapter is concerned with the sanitation of ‘hard’ surfaces only –
equipment, floors, walls and utensils – as other surfaces, e.g. protective clothing
14
Cleaning and disinfection
J. Holah, Campden and Chorleywood Food Research Association
or skin, have been dealt with under personal hygiene (Chapter 13). In this
context, surface sanitation is undertaken to:
? remove microorganisms, or material conductive to microbial growth. This
reduces the chance of contamination by pathogens and, by reducing spoilage
organisms, may extend the shelf-life of some products.
? remove materials that could lead to foreign body contamination or could
provide food or shelter for pests. This also improves the appearance and
quality of product by removing food materials left on lines that may
deteriorate and re-enter subsequent production runs.
? extend the life of, and prevent damage to equipment and services, provide a
safe and clean working environment for employees and boost morale and
productivity.
? present a favourable image to customers and the public. On audit, the initial
perception of an ‘untidy’ or ‘dirty’ processing area, and hence a ‘poorly
managed operation’ is subsequently difficult to overcome.
14.2 Sanitation principles
Sanitation is undertaken primarily to remove all undesirable material (food
residues, microorganisms, foreign bodies and cleaning chemicals) from surfaces
in an economical manner, to a level at which any residues remaining are of
minimal risk to the quality or safety of the product. Such undesirable material,
generally referred to as ‘soil’, can be derived from normal production, spillages,
line-jams, equipment maintenance, packaging or general environmental
contamination (dust and dirt). To undertake an adequate and economic
sanitation programme, it is essential to characterise the nature of the soil to
be removed.
The product residues are readily observed and may be characterised by their
chemical composition, e.g. carbohydrate, fat, protein or starch. It is also
important to be aware of processing and/or environmental factors, however, as
the same product soil may lead to a variety of cleaning problems dependent
primarily on moisture levels and temperature. Generally, the higher the product
soil temperature (especially if the soil has been baked) and the greater the time
period before the sanitation programme is initiated (i.e. the drier the soil
becomes), the more difficult the soil is to remove.
Microorganisms can either be incorporated into the soil or can attach to
surfaces and form layers or biofilms. There are a number of factors that have
been shown to affect attachment and biofilm formation such as the level and
type of microorganisms present, surface conditioning layer, substratum nature
and roughness, temperature, pH, nutrient availability and time available. Several
reviews of biofilm formation in the food industry have been published including
Pontefract (1991), Holah and Kearney (1992), Mattila-Sandholm and Wirtanen
(1992), Carpentier and Cerf (1993), Zottola and Sasahara (1994), Gibson et al.
398 Chilled foods
(1995) and Kumar and Anand, (1998). In general, however, biofilm formation is
usually found only on environmental surfaces, and progression of attached cells
through microcolonies to extensive biofilm is limited by regular cleaning and
disinfection.
Gibson et al.(1995) in studies of attached microorganisms in 17 different
processing environments, recorded 79% of isolates as Gram negative rods, 8.6%
Gram positive cocci, 6.5% Gram positive rods and 1.2% yeast strains. The most
common organisms were Pseudomonas, Staphylococcus and Enterobacter spp.
Pseudomonads are environmental psychrotrophic organisms that readily attach to
surfaces and are common spoilage organsisms in chilled foods. Other common
Gram negatives that have been associated with surfaces are coliform organisms
that are widely distributed in the environment and may also be indicators of
inadequate processing or post process contamination. Staphylococci are
associated with human skin and therefore their presence on surfaces may be as
a result of transfer from food handlers. In addition, Mettler and Carpentier (1998)
studied the microflora associated with the surfaces in milk, meat and pastry sites
and concluded that the micro-flora was specific to the processing environment.
Bacteria adhering to the food product contact surfaces may be an important
source of potential contamination leading to serious hygienic problems and
economic losses due to food spoilage. For example, pseudomonads and many
other Gram negative organisms detected on surfaces are the spoilage organisms
of concern in chilled foods. The survival of organisms in biofilms may be a
source of post process contamination, resulting in reduced shelf life of the
product. In addition, Listeria monocytogenes has been isolated from a range of
food processing surfaces (Walker et al. 1991, Lawrence and Gilmore 1995 and
Destro et al. 1996) and is usually looked for in high-risk processing areas via the
company environmental sampling plan.
Following HACCP principles, if the food processor believes that biofilms are
a risk to the safety of the food product, appropriate control steps must be taken.
These would include providing an environment in which the formation of the
biofilm would be limited, undertaking cleaning and disinfection programmes as
required, monitoring and controlling these programmes to ensure their success
during their operation and verifying their performance by a suitable (usually
microbiological) assessment.
Within the sanitation programme, the cleaning phase can be divided up into
three stages, following the pioneering work of Jennings (1965) and interpreted
by Koopal (1985), with the addition of a fourth stage to cover disinfection.
These are described below.
1. The wetting and penetration by the cleaning solution of both the soil and the
equipment surface.
2. The reaction of the cleaning solution with both the soil and the surface to
facilitate: peptisation of organic materials, dissolution of soluble organics
and minerals, emulsification of fats and the dispersion and removal from the
surface of solid soil components.
Cleaning and disinfection 399
3. The prevention of redeposition of the dispersed soil back onto the cleansed
surface.
4. The wetting by the disinfection solution of residual microorganisms to
facilitate reaction with cell membranes and/or penetration of the microbial
cell to produce a biocidal or biostatic action. Dependent on whether the
disinfectant contains a surfactant and the disinfectant practice chosen (i.e.
with or without rinsing), this may be followed by dispersion of the
microorganisms from the surface.
To undertake these four stages, sanitation programmes employ a combination
of four major factors as described below. The combinations of these four factors
vary for different cleaning systems and, generally, if the use of one energy
source is restricted, this short-fall may be compensated for by utilising greater
inputs from the others.
1. mechanical or kinetic energy
2. chemical energy
3. temperature or thermal energy
4. time.
Mechanical or kinetic energy is used to remove soils physically and may include
scraping, manual brushing and automated scrubbing (physical abrasion) and
pressure jet washing (fluid abrasion). Of all four factors, physical abrasion is
regarded as the most efficient in terms of energy transfer (Offiler 1990), and the
efficiency of fluid abrasion and the effect of impact pressure has been described
by Anon. (1973) and Holah (1991). Mechanical energy has also been
demonstrated to be the most efficient for biofilm removal (Blenkinsopp and
Costerton 1991, Wirtanen and Mattila Sandholm 1993, 1994, Mattila-Sandholm
and Wirtanen 1992 and Gibson et al. 1999).
In cleaning, chemical energy is used to break down soils to render them
easier to remove and to suspend them in solution to aid rinsability. At the time of
writing, no cleaning chemical has been marketed with the benefit of aiding
microorganism removal. In chemical disinfection, chemicals react with
microorganisms remaining on surfaces after cleaning to reduce their viability.
The chemical effects of cleaning and disinfection increase with temperature in a
linear relationship and approximately double for every 10oC rise. For fatty and
oily soils, temperatures above their melting point are used, to break down and
emulsify these deposits and so aid removal. The influence of detergency in
cleaning and disinfection has been described by Dunsmore (1981), Shupe et al.
(1982), Mabesa et al. (1982), Anderson et al. (1985) and Middlemiss et al.
(1985). For cleaning processes using mechanical, chemical and thermal
energies, generally the longer the time period employed, the more efficient
the process. When extended time periods can be employed in sanitation
programmes, e.g. soak-tank operations, other energy inputs can be reduced (e.g.
reduced detergent concentration, lower temperature or less mechanical
brushing).
400 Chilled foods
Soiling of surfaces is a natural process which reduces the free energy of the
system. To implement a sanitation programme, therefore, energy must be added
to the soil to reduce both soil particle-soil particle and soil particle-equipment
surface interactions. The mechanics and kinetics of these interactions have been
discussed by a number of authors (Jennings 1965, Schlussler 1975, Loncin 1977,
Corrieu 1981, Koopal 1985, Bergman and Tragardh 1990), and readers are
directed to these articles since they fall beyond the scope of this chapter. In
practical terms, however, it is worth looking at the principles involved in basic
soil removal, as they have an influence on the management of sanitation
programmes.
Soil removal from surfaces decreases such that the log of the mass of soil per
unit area remaining is linear with respect to cleaning time (Fig. 14.1(a)) and thus
follows first-order reaction kinetics (Jennings 1965, Schlusser 1975). This
approximation, however, is only valid in the central portion of the plot and, in
practice, soil removal is initially faster and ultimately slower (dotted line in Fig.
14.1(a)) than that which a first-order reaction predicts. The reasons for this are
unclear, though initially, unadhered, gross oil is usually easily removed (Loncin
1977) whilst ultimately, soils held within surface imperfections, or otherwise
protected from cleaning effects, would be more difficult to remove (Holah and
Thorpe 1990).
Routine cleaning operations are never, therefore, 100% efficient, and over a
course of multiple soiling/cleaning cycles, soil deposits (potentially including
microorganisms) will be retained. As soil accumulates, cleaning efficiency will
decrease and, as shown in plot A, Fig. 14.1(b), soil deposits may for a period
grow exponentially. The timescale for such soil accumulation will differ for all
Fig. 14.1 Soil removal and accumulation. (a) Removal of soil with cleaning time. Solid
line is theoretical removal, dotted line is cleaning in practice. (b) Build up of soil (and/or
microorganisms); A, without periodic cleans and B, with periodic cleans. (After
Dunsmore et al. 1981).
Cleaning and disinfection 401
processing applications and can range from hours (e.g. heat exchangers) to
typically several days or weeks, and in practice is controlled by the application
of a ‘periodic’ clean (Dunsmore et al. 1981). Periodic cleans are employed to
return the surface-bound soil accumulation to an acceptable base level (plot B,
Fig. 14.1(b)) and are achieved by increasing cleaning time and/or energy input,
e.g. higher temperatures, alternative chemicals or manual scrubbing. A typical
example of a periodic clean is the ‘week-end clean down’ or ‘bottoming’.
14.3 Sanitation chemicals
In many instances, management view the costs of cleaning and disinfection as
the price of the chemicals purchased, primarily because this is the only ‘invoice’
that they see. In reality, however, sanitation chemicals are likely to represent
approximately only 5% of the true costs, with labour and water costs being the
most significant. The purchase of a good quality formulated cleaning product,
whilst being initially more expensive, will more than cover its costs by
increasing both the standard of clean and cleaning efficiency.
Within the sanitation programme it has traditionally been recognised that
cleaning is responsible for the removal of not only the soil but also the majority
of the microorganisms present. Mrozek (1982) showed a reduction in bacterial
numbers on surfaces by up to 3 log orders whilst Schmidt and Cremling (1981)
described reductions of 2–6 log orders. The results of work at CCFRA on the
assessment of well constructed and competently undertaken sanitation
programmes on food processing equipment in eight chilled food factories is
shown in Table 14.1. The results suggest that both cleaning and disinfection are
equally responsible for reducing the levels of adhered microorganisms. It is
important, therefore, not only to purchase quality cleaning chemicals for their
soil removal capabilities but also for their potential for microbial removal.
Unfortunately no single cleaning agent is able to perform all the functions
necessary to facilitate a successful cleaning programme; so a cleaning solution,
or detergent, is blended from a range of typical characteristic components:
? water
? surfactants
? inorganic alkalis
Table 14.1 Arithmetic and log mean bacterial counts on food processing equipment
before and after cleaning and after disinfection
Before cleaning After cleaning After disinfection
Arithmetic mean 1.32C210
6
8.67C210
4
2.5C210
3
log mean 3.26 2.35 1.14
No. of observations 498 1090 3147
402 Chilled foods
? inorganic and organic acids
? sequestering agents.
For the majority of food processing operations it may be necessary, therefore, to
employ a number of cleaning products, for specific operations. This requirement
must be balanced by the desire to keep the range of cleaning chemicals on site to
a minimum so as to reduce the risk of using the wrong product, to simplify the
job of the safety officer and to allow chemical purchase to be based more on the
economics of bulk quantities. The range of chemicals and their purposes is well
documented (Anon. 1991, Elliot 1980, ICMSF 1980, 1988, Hayes 1985, Holah
1991, Koopal 1985, Russell et al. 1982) and only an overview of the principles
is given here.
Water is the base ingredient of all ‘wet’ cleaning systems and must be of
potable quality. Water provides the cheapest readily available transport medium
for rinsing and dispersing soils, has dissolving powers to remove ionic-soluble
compounds such as salts and sugars, will help emulsify fats at temperatures
above their melting point, and, in high-pressure cleaning, can be used as an
abrasive agent. On its own, however, water is a poor ‘wetting’ agent and cannot
dissolve non-ionic compounds.
Organic surfactants (surface-active or wetting agents) are amphipolar and are
composed of a long non-polar (hydrophobic or lyophilic) chain or tail and a
polar (hydrophilic or lyophobic) head. Surfactants are classified as anionic
(including the traditional soaps), cationic, or non-ionic, depending on their ionic
charge in solution, with anionics and non-ionics being the most common.
Amphipolar molecules aid cleaning by reducing the surface tension of water and
by emulsification of fats. If a surfactant is added to a drop of water on a surface,
the polar heads disrupt the water’s hydrogen bonding and so reduce the surface
tension of the water and allow the drop to collapse and ‘wet’ the surface.
Increased wettability leads to enhanced penetration into soils and surface
irregularities and hence aids cleaning action. Fats and oils are emulsified as the
hydrophilic heads of the surfactant molecules dissolve in the water whilst the
hydrophobic end dissolves in the fat. If the fat is surface-bound, the forces acting
on the fat/water interface are such that the fat particle will form a sphere (to
obtain the lowest surface area for its given volume) causing the fat deposit to
‘roll-up’ and detach itself from the surface.
Alkalis are useful cleaning agents as they are cheap, break down proteins
through the action of hydroxyl ions, saponify fats and, at higher concentrations,
may be bactericidal. Strong alkalis, usually sodium hydroxide (or caustic soda),
exhibit a high degree of saponification and protein disruption, though they are
corrosive and hazardous to operatives. Correspondingly, weak alkalis are less
hazardous but also less effective. Alkaline detergents may be chlorinated to aid
the removal of proteinaceous deposits, but chlorine at alkaline pH is not an
effective biocide. The main disadvantages of alkalis are their potential to
precipitate hard water ions, the formation of scums with soaps, and their poor
rinsability.
Cleaning and disinfection 403
Acids have little detergency properties, although they are very useful in
making soluble carbonate and mineral scales, including hard water salts and
proteinaceous deposits. As with alkalis, the stronger the acid the more effective
it is; though, in addition, the more corrosive to plant and operatives. Acids are
not used as frequently as alkalis in chilled food operations and tend to be used
for periodic cleans.
Sequestering agents (sequestrants or chelating agents) are employed to
prevent mineral ions precipitating by forming soluble complexes with them.
Their primary use is in the control of water hardness ions and they are added to
surfactants to aid their dispersion capacity and rinsability. Sequestrants are most
commonly based on ethylene diamine tetracetic acid (EDTA), which is
expensive. Although cheaper alternatives are available, these are usually
polyphosphates which are environmentally unfriendly.
A general-purpose food detergent may, therefore, contain a strong alkali to
saponify fats, weaker alkali ‘builders’ or ‘bulking’ agents, surfactants to improve
wetting, dispersion and rinsability and sequestrants to control hard water ions. In
addition, the detergent should ideally be safe, non-tainting, non-corrosive, stable,
environmentally friendly and cheap. The choice of cleaning agent will depend on
the soil to be removed and on its solubility characteristics, and these are summar-
ised for a range of chilled products in Table 14.2 (modified from Elliot 1980).
Because of the wide range of food soils likely to be encountered and the
influence of the food manufacturing site (temperature, humidity, type of
equipment, time before cleaning, etc.), there are currently no recognised
laboratory methods for assessing the efficacy of cleaning compounds. Food
manufacturers have to be satisfied that cleaning chemicals are working
appropriately, by conducting suitable field trials. Although the majority of the
microbial contamination is removed by the cleaning phase of the sanitation
Table 14.2 Solubility characteristics and cleaning procedures recommended for a range
of soil types
Soil type Solubility characteristics Cleaning procedure
recommended
Sugars, organic acids, salt Water-soluble Mildly alkaline detergent
High protein foods (meat, Water-soluble Chlorinated alkaline detergent
poultry, fish) Alkali-soluble
Slightly acid-soluble
Starchy foods, tomatoes, Partly water-soluble Mildly alkaline detergent
fruits Alkali-soluble
Fatty foods (fat, butter, Water-insoluble Mildly alkaline detergent; if
margarine, oils) Alkaline-soluble ineffective, use strong alkali
Heat-precipitated water Water-insoluble Acid cleaner, used on a
hardness, milk stone, Alkaline-insoluble periodic basis
protein scale Acid-soluble
404 Chilled foods
programme, there are likely to be sufficient viable microorganisms remaining on
the surface to warrant the application of a disinfectant. The aim of disinfection is
therefore to further reduce the surface population of viable microorganisms, via
removal or destruction, and/or to prevent surface microbial growth during the
inter-production period. Elevated temperature is the best disinfectant as it
penetrates into surfaces, is non-corrosive, is non-selective to microbial types, is
easily measured and leaves no residue (Jennings 1965). However, for open
surfaces, the use of hot water or steam is uneconomic, hazardous or impossible,
and reliance is, therefore, placed on chemical biocides.
Whilst there are many chemicals with biocidal properties, many common
disinfectants are not used in food applications because of safety or taint
problems, e.g. phenolics or metal-ion-based products. In addition, other
disinfectants are used to a limited extent only in chilled food manufacture
and/or for specific purposes, e.g. peracetic acid, biguanides, formaldehyde,
glutaraldehyde, organic acids, ozone, chlorine dioxide, bromine and iodine
compounds. Of the acceptable chemicals, the most commonly used products are:
? chlorine-releasing components
? quaternary ammonium compounds
? amphoterics
? quaternary ammonium/amphoteric mixtures.
Chlorine is the cheapest disinfectant and is available as hypochlorite (or
occasionally as chlorine gas) or in slow releasing forms (e.g. chloramines,
dichlorodimethylhydantoin). Quaternary ammonium compounds (Quats or
QACs) are amphipolar, cationic detergents, derived from substituted ammonium
salts with a chlorine or bromine anion and amphoterics are based on the amino
acid glycine, often incorporating an imidazole group.
In a (CCFRA) survey undertaken of the UK food industry in 1987, of 145
applications of disinfectants 52% were chlorine based, 37% were quaternary
ammonium compounds and 8% were amphoterics. Of these biocides there were,
respectively, 44, 30 and 8 branded products used. In a (CCFRA) European
survey of 1993, the most common disinfectants used in the UK and
Scandinavian countries were QACs for open surfaces and peracetic acid and
chlorine for closed, liquid handling surfaces. The survey also showed that open
surfaces were usually cleaned with alkaline detergents which were foamed and
then rinsed with medium pressure water (250psi) and closed systems were CIP
cleaned with caustic followed by acidic detergents with a suitable rinse in-
between. A survey of the approved disinfectant products in Germany (DVG
listed) in 1994 indicated that 36% were QACs, 20% were mixtures of QACs
with aldehydes or biguanides and 10% were amphoterics (Knauer-Kraetzl
1994). More recently the synergistic combinations of QACs and amphoterics
have been explored in the UK and these compounds are now widely used in
chilled food plants. The characteristics of the most commonly used are
compared in Table 14.3. The properties of QAC/amphoteric mixes will be
similar to their parent compounds with often enhanced microorganism control.
Cleaning and disinfection 405
Within the chilled food industry, particularly for mid-shift cleaning and
disinfection in high-risk areas, alcohol based products are commonly used. This
is primarily to restrict the use of water for cleaning during production as a
control measure to prevent the growth and spread of any food pathogens that
penetrate the high-risk area barrier controls. Ethyl alcohol (ethanol) and
isopropyl alcohol (isopropanol) have bactericidal and virucidal (but not
sporicidal) properties (Hugo and Russell 1999), though they are only active in
the absence of organic matter i.e. the surfaces need to be wiped clean and then
alcohol reapplied. Alcohols are most active in the 60–70% range, and can be
formulated into wipe and spray based products. Alcohol products are used on a
small, local scale because of their well recognised health and safety issues.
The efficacy of disinfectants is generally controlled by five factors:
interfering substances (primarily organic matter), pH, temperature, concentra-
tion and contact time. To some extent, and particularly for the oxidative
biocides, the efficiency of all disinfectants is reduced in the presence of organic
matter. Organic material may react chemically with the disinfectant such that it
loses its biocidal potency, or spatially such that microorganisms are protected
from its effect. Other interfering substances, e.g. cleaning chemicals, may react
Table 14.3 Characteristics of some universal disinfectants
Property Chlorine QAC Amphoteric Peracetic
acid
Microorganism control
Gram-positive + + + + + + + +
Gram-negative + + + + + + +
Spores + C0C0 ++
Yeast + + + + + + + +
Developed microbial resistance C0 ++ C0
Inactivation by organic matter + + + + +
water hardness C0 + C0C0
Detergency properties C0 ++ + C0
Surface activity C0 ++ ++ C0
Foaming potential C0 ++ ++ C0
Problems with taints +/C0C0 C0 +/C0
Stability +/C0C0 C0 +/C0
Corrosion + C0C0 C0
Safety + C0C0 ++
Other chemicals C0 + C0C0
Potential environmental impact + + C0/+ C0/+ C0
Cost C0 ++ ++ +
C0 no effect (or problem).
+ effect.
+ + large effect.
406 Chilled foods
with the disinfectant and destroy its antimicrobial properties, and it is therefore
essential to remove all soil and chemical residues prior to disinfection.
Disinfectants should be used only within the pH range as specified by the
manufacturer. Perhaps the classic example of this is chlorine, which dissociates
in water to form HOCl and the OCl ion. From pH 3–7.5, chlorine is
predominantly present as HOCl, which is a very powerful biocide, though the
potential for corrosion increases with acidity. Above pH 7.5, however, the
majority of the chlorine is present as the OCl ion which has about 100 times less
biocidal action than HOCl.
In general, the higher the temperature the greater the disinfection. For most
food manufacturing sites operating at ambient conditions (around 20oC) or
higher this is not a problem as most disinfectants are formulated (and tested) to
ensure performance at this temperature. This is not, however, the case in the
chilled food industry. Taylor et al. (1999) examined the efficacy of 18
disinfectants at both 10oC and 20oC and demonstrated that for some chemicals,
particularly quaternary ammonium based products, disinfection was much
reduced at 10oC and recommended that in chilled production environments,
only products specifically formulated for low-temperature activity should be
used.
In practice, the relationship between microbial death and disinfectant
concentration is not linear but follows a sigmoidal curve. Microbial populations
are initially difficult to kill at low concentrations, but as the biocide
concentration is increased, a point is reached where the majority of the
population is reduced. Beyond this point the microorganisms become more
difficult to kill (through resistance or physical protection) and a proportion may
survive regardless of the increase in concentration. It is important, therefore, to
use the disinfectant at the concentration as recommended by the manufacturer.
Concentrations above this recommended level may thus not enhance biocidal
effect and will be uneconomic whilst concentrations below this level may
significantly reduce biocidal action.
Sufficient contact time between the disinfectant and the microorganisms is
perhaps the most important factor controlling biocidal efficiency. To be
effective, disinfectants must find, bind to and transverse microbial cell
envelopes before they reach their target site and begin to undertake the
reactions which will subsequently lead to the destruction of the microorganism
(Klemperer 1982). Sufficient contact time is therefore critical to give good
results, and most general-purpose disinfectants are formulated to require at least
five minutes to reduce bacterial populations by five log orders in suspension.
This has arisen for two reasons. Firstly five minutes is a reasonable
approximation of the time taken for disinfectants to drain off vertical or near
vertical food processing surfaces. Secondly, when undertaking disinfectant
efficacy tests in the laboratory, a five-minute contact time is chosen to allow
ease of test manipulation and hence timing accuracy. For particularly resistant
organisms such as spores or moulds, surfaces should be repeatedly dosed to
ensure extended contact times of 15–60 minutes.
Cleaning and disinfection 407
Ideally, disinfectants should have the widest possible spectrum of activity
against microorganisms, including bacteria, fungi, spores and viruses, and this
should be demonstrable by means of standard disinfectant efficacy tests. The range
of currently available disinfectant test methods was reviewed by Reybrouck (1998)
and fall into two main classes, suspension tests and surface tests. Suspension tests
are useful for indicating general disinfectant efficacy and for assessing
environmental parameters such as temperature, contact time and interfering matter
such as food residues. In reality however, microorganisms disinfected on food
contact surfaces are those that remain after cleaning and are therefore likely to be
adhered to the surface. A surface test is thus more appropriate.
A number of authors have shown that bacteria attached to various surfaces
are generally more resistant to biocides than are organisms in suspension
(Dhaliwal et al. 1992, Frank and Koffi 1990, Holah et al. 1990a, Hugo et al.
1985, Le Chevalier et al. 1988, Lee and Frank 1991, Ridgeway and Olsen 1982,
Wright et al. 1991, Andrade et al. 1998, Das et al. 1998). In addition, cells
growing as a biofilm have been shown to be more resistant (Frank and Koffi
1990, Lee and Frank 1991, Ronner and Wong 1993). The mechanism of
resistance in attached and biofilm cells is unclear but may be due to
physiological differences such as growth rate, membrane orientation changes
due to attachment and the formation of extracellular material which surrounds
the cell. Equally, physical properties may have an effect e.g. protection of the
cells by food debris or the material surface structure or problems in biocide
diffusion to the cell/material surface. To counteract such claims of enhanced
surface adhered resistance, it can be argued that in reality, surface tests do not
consider the environmental stresses the organisms may encounter in the
processing environment prior to disinfection (action of detergents, variations in
temperature and pH and mechanical stresses) which may affect susceptibility.
Both suspension and surface tests have limitations, however, and research based
methods are being developed to investigate the effect of disinfectants against
adhered microorganisms and biofilms in-situ and in real time. Such methods
have been reviewed by Holah et al. (1998).
In Europe, CEN TC 216 is currently working to harmonise disinfectant
testing and has produced a number of standards. The current food industry
disinfectant test methods of choice for bactericidal and fungicidal action in
suspension are EN 1276 (Anon. 1997) and EN 1650 (Anon. 1998a) respectively
and food manufacturers should ensure that the disinfectants they use conform to
these standards as appropriate. A harmonised surface test is expected in 2000.
Because of the limitations of disinfectant efficacy tests, however, food
manufacturers should always confirm the efficacy of their cleaning and
disinfection programmes by field tests either from evidence supplied by the
chemical company or from in-house trials.
As well as having demonstrable biocidal properties, disinfectants must also
be safe (non-toxic) and should not taint food products. Disinfectants can enter
food products accidentally e.g. from aerial transfer or poor rinsing, or
deliberately e.g. from ‘no rinse status’ disinfectants. The practice of rinsing or
408 Chilled foods
not rinsing has yet to be established. The main reason for leaving disinfectants
on surfaces is to provide an alleged biocide challenge (this has not been proven)
to any subsequent microbial contamination of the surface. It has been argued,
however, that the low biocide concentrations remaining on the surface,
especially if the biocide is a QAC, may lead to the formation of resistant
surface populations.
In Europe, legislation is confusing surrounding whether or not disinfectants can
be left on surfaces without rinsing. The Meat Products Directive (95/68/EC) allows
disinfectants to remain on surfaces (no rinse status) ‘when the directions for use of
such substances render such rinsing unnecessary’, whilst the Egg Products (89/437/
EEC) and Milk Products (92/46/EEC) Directives require that disinfectants must be
rinsed off by potable water. There is no specific guidance for other food product
categories although the general Directive on the hygiene of foodstuffs (93/43/EEC)
requires ‘Food business operators shall identify any step in their activities which is
critical to ensuring food safety and ensure that adequate safety procedures are
identified, implemented, maintained and reviewed. . .’.
In terms of the demonstration of non-toxicity, legislation will vary in each
country although in Europe, this will be clarified with the implementation of
Directive 98/9/EC concerning the placing of biocidal products on the market,
which contains requirements for toxicological and metabolic studies. A
recognised acceptable industry guideline for disinfectants is a minimum acute
oral toxicity (with rats) of 2,000 mg/Kg bodyweight.
Approximately 30% of food taint complaints are thought to be associated
with cleaning and disinfectant chemicals and are described by sensory scientists
as ‘soapy’, ‘antiseptic’ or ‘disinfectant’ (Holah 1995). CCFRA have developed
two taint tests in which foodstuffs which have and have not been exposed to
disinfectant residues are compared by a trained taste panel using the standard
triangular taste test (Anon. 1983a). For assessment of aerial transfer, a
modification of a packaging materials odour transfer test is used (Anon. 1964)
in which food products, usually of four types (high moisture e.g. melon, low
moisture e.g. biscuit, high fat e.g. cream, high protein e.g. chicken) are held
above disinfectant solution of distilled water for 24 hours. To assess surface
transfer, a modification or a food container transfer test is used (Anon. 1983b) in
which food products are sandwiched between two sheets of stainless steel and
left for 24 hours. Disinfectants can be sprayed onto the stainless steel sheets and
drained off, to simulate no rinse status, or can be rinsed off prior to food contact.
Control sheets are rinsed in distilled water only. The results of the triangular test
involve both a statistical assessment of any flavour differences between the
control and disinfectant treated sample and a description of any flavour changes.
14.4 Sanitation methodology
Cleaning and disinfection can be undertaken by hand using simple tools, e.g.
brushes or cloths (manual cleaning), though as the area of open surface requiring
Cleaning and disinfection 409
cleaning and disinfection increases, specialist equipment becomes necessary to
dispense chemicals and/or provide mechanical energy. Chemicals may be
applied as low pressure mists, foams or gels whilst mechanical energy is
provided by high and low pressure water jets or water or electrically powered
scrubbing brushes. These techniques have been well documented (Anon. 1991,
Marriott 1985, Holah 1991) and this section considers their use in practice.
The use of cleaning techniques can perhaps be described schematically
following the information detailed in Fig. 14.2. The figure details the different
energy source inputs for a number of cleaning techniques and shows their ability
to cope with both low and high (dotted line) levels of soiling. For the manual
cleaning of small items a high degree of mechanical energy can be applied
directly where it is needed and with the use of soak tanks (or clean-out-of-place
techniques) contact times can be extended and/or chemical and temperature
inputs increased such that all soil types can be tackled.
Alternatively, dismantled equipment and production utensils may undergo
manual gross soil removal and then be cleaned and disinfected automatically in
tray or tunnel washers. As with soak tank operations, high levels of chemical and
thermal energy can be used to cope with the majority of soils. The siting of tray
washes in high-risk chilled production areas should be carefully considered,
however, as they are prone to microbial aerosol production which may lead to
aerial product contamination (see Chapter 13).
In manual cleaning of larger areas, for reasons of operator safety, only low
levels of temperature and chemical energy can be applied, and as the surface
area requiring cleaning increases, the technique becomes uneconomic with
respect to time and labour. Labour costs amount to 75% of the total sanitation
programme and for most food companies, the cost of extra staff is prohibitive.
Only light levels of soiling can be economically undertaken by this method.
The main difference between the mist, foam and gel techniques is in their
ability to maintain a detergent/soil/surface contact time. For all three techniques,
mechanical energy can be varied by the use of high or low-pressure water rinses,
though for open surface cleaning, temperature effects are minimal. Mist
spraying is undertaken using small hand-pumped containers, ‘knapsack’
sprayers or pressure washing systems at low pressure. Misting will only ‘wet’
vertical smooth surfaces; therefore only small quantities can be applied and
these will quickly run off to give a contact time of five minutes or less. Because
of the nature of the technique to form aerosols that could be an inhalation
hazard, only weak chemicals can be applied, and so misting is useful only for
light soiling. On cleaned surfaces, however, misting is the most commonly used
method for applying disinfectants.
Foams can be generated and applied by the entrapment of air in high-pressure
equipment or by the addition of compressed air in low-pressure systems. Foams
work on the basis of forming a layer of bubbles above the surface to be cleaned
which then collapses and bathes the surface with fresh detergent contained in the
bubble film. The critical element in foam generation is for the bubbles to
collapse at the correct rate: too fast and the contact time will be minimal; too
410 Chilled foods
Fig. 14.2 Relative energy source inputs for a range of cleaning techniques. (Modified from Offiler 1990).
slow and the surface will not be wetted with fresh detergent. Gels are thixotropic
chemicals which are fluid at high and low concentrations but become thick and
gelatinous at concentrations of approximately 5–10%. Gels are easily applied
through high- and low-pressure systems or from specific portable electric
pumped units and physically adhere to the surface.
Foams and gels are more viscous than mists, are not as prone to aerosol
formation and thus allow the use of more concentrated detergents, and can
remain on vertical surfaces for much longer periods (foams 10–15 minutes, gels
15 minutes to an hour or more). Foams and gels are able to cope with higher
levels of soils than misting, although in some cases rinsing of surfaces may
require large volumes of water, especially with foams. Foams and gels are well
liked by operatives and management, because of the nature of the foam, a more
consistent application of chemicals is possible and it is easier to identify areas
that have been ‘missed’.
Fogging systems have been traditionally used in the chilled food industry to
create and disperse a disinfectant aerosol to reduce airborne microorganisms and
to apply disinfectant to difficult to reach overhead surfaces. The efficacy of
fogging was recently examined in the UK and has been reported (Anon. 1998b).
Providing a suitable disinfectant is used, fogging is effective at reducing
airborne microbial populations by 2–3 log orders in 30–60 minutes. Fogging is
most effective using compressed air driven fogging nozzles producing particles
in the 10–20 micron range. For surface disinfection, fogging is effective only if
sufficient chemical can be deposited onto the surface. This is illustrated in
Figure 14.3 which shows the log reductions achieved on horizontal, vertical and
upturned (underneath) surfaces arranged at five different heights from just below
the ceiling (276 cm) to just above the floor (10 cm) within a test room. It can be
seen that disinfection is greatest on surfaces closest to the floor and that
disinfection is minimal on upturned surfaces close to the ceiling. To reduce
inhalation risks, sufficient time (45–60 minutes) is required after fogging to
Fig. 14.3 Comparative log reductions of microorganisms adhered to surfaces and
positioned at various heights and orientations.
412 Chilled foods
allow the settling of disinfectant aerosols before operatives can re-enter the
production area.
Cleaning chemicals are removed from surfaces by low-pressure/high-volume
hoses operating at mains water pressure or by high-pressure/low volume pressure
washing systems. Pressure washing systems typically operate at between 25–100
bar through a 15o nozzle and may be mobile units, wall mounted units or
centralised ring-mains. Water jets confer high mechanical energy, can be used on
a wide range of equipment and environmental surfaces, will penetrate into surface
irregularities and are able to mix and apply chemicals.
Mechanical scrubbers include traditional floor scrubbers, scrubber/driers
(automats) for floors, and water-driven attachments to high pressure systems and
electrically operated small-diameter brushes that can be used on floors, walls
and other surfaces. Contact time is usually limited with these techniques (though
can be increased), but the combination of detergency with high mechanical input
allows them to tackle most soil types. The main limitation is that food-
processing areas have not traditionally been designed for their use, though this
can be amended in new or refurbished areas.
The hygienic implications of the design and use of cleaning equipment
should be carefully considered. Sanitation equipment should be constructed out
of smooth, non-porous, easily cleanable materials such as stainless steel or
plastic. Mild steel or other materials subject to corrosion may be used but must
be suitably painted or coated, whilst the use of wood is unacceptable.
Frameworks should be constructed of tubular or box section material, closed at
either end and properly jointed, e.g. welds should be ground and polished and
there should be no metal-to-metal joints. Crevices and ledges where soil could
collect should be avoided and exposed threads should be covered or dome nuts
used. Tanks for holding cleaning chemicals or recovered liquids should be self-
draining, have rounded corners and should be easily cleaned. Shrouds around
brush heads or hoods and rotary scrubbing heads should be easily detachable to
facilitate cleaning. Brushes should have bristles of coloured, impervious
material, e.g. nylon, embedded into the head with resin so no soil trap points
are apparent. Alternatively, brushes with the head and bristles moulded as one
unit may be used.
Cleaning equipment is prone to contamination with Listeria spp. and other
pathogenic microoganisms and, by the nature of its use, provides an excellent
way in which contamination can be transferred from area to area. Cleaning
equipment should be specific to high risk and after use, equipment should be
thoroughly cleaned and, if appropriate, disinfected and dried. The potential for
cleaning equipment to disperse microbial contamination by the formation of
aerosols has been reported (Holah et al. 1990b) and it was shown that all
cleaning systems tested produced viable bacterial aerosols from test surfaces
contaminated with attached biofilms.
The degree of contamination impinging on a surface was graded from total
coverage to the minimum level thought likely to give concern if a proportion of
the droplets contained viable microorganisms and the maximum height and
Cleaning and disinfection 413
distance travelled by this contamination level is shown in Table 14.4. Assuming
an average food contact surface height of 1 m, the results suggest that both the
high pressure low-volume (HPLV) and low pressure high-volume (LPHV)
techniques disperse a significant level of aerosol to this height and should not,
therefore, be used during production periods. The other techniques, however, are
acceptable for use in clean-as-you-go operations as the chance of contamination
to product is low, though care is needed when using floor scrubber/driers (these
are useful in that the cleaning fluid is removed from the floor) if product is
stored in racks close to the floor. After production, HPLV and LPHV techniques
may be safely used (and are likely to be the appropriate choice), but it is required
that disinfection of food contact surfaces is the last operation to be performed
within the sanitation programme. Subsequent work has shown that reducing
water pressure or changing impact angle made little difference to the degree of
aerosol spread for HPLV and LPHV systems, dispersal to heights C621 m still
being achieved.
14.5 Sanitation procedures
Sanitation procedures are concerned with both the stage at which the sanitation
programme is implemented and the sequence in which equipment and
environmental surfaces are cleaned and disinfected within the processing area.
Sanitation programmes are so constructed as to be efficient with water and
chemicals, to allow selected chemicals to be used under their optimum
conditions, to be safe in operation, to be easily managed and to reduce manual
labour. In this way an adequate level of sanitation will be achieved,
economically and with due regard to environmental friendliness. The principal
stages involved in a typical sanitation programme are described below.
Production periods. Production staff should be encouraged to consider the
implications of production practices on the success of subsequent sanitation
programmes. Product should be removed from lines during break periods and
this may be followed by manual cleaning, usually undertaken by wiping with
Table 14.4 Maximum height and distance of aerosol impingement for a
number of cleaning techniques
Cleaning technique Height (cm) Distance (cm)
High-pressure/low-volume spray lance 309 700
Low-pressure/high-volume hose 210 350
Floor scrubber/drier 47 80
Manual brushing 24 75
Manual wiping 23 45
414 Chilled foods
alcohol (to avoid the use of water during production periods). Production staff
should also be encouraged to operate good housekeeping practices (this is also
an aid to ensuring acceptable product quality) and to leave their work stations in
a reasonable condition. Soil left in hoppers and on process lines, etc. is wasted
product! Sound sanitation practices should be used to clean up large product
spillages during production.
Preparation. As soon as possible after production, equipment should be
dismantled as far as is practicable or necessary to make all surfaces that
microorganisms could have adhered to during production accessible to the
cleaning fluids. All unwanted utensils/packaging/equipment should be covered
or removed from the area. Dismantled equipment should be stored on racks or
tables, not on the floor! Machinery should be switched off, at the machine and at
the power source, and electrical and other sensitive systems protected from
water/chemical ingress. Preferably, production should not occur in the area
being cleaned, but in exceptional circumstances if this is not possible, other lines
or areas should be screened off to prevent transfer of debris by the sanitation
process.
Gross soil removal. Where appropriate, all loosely adhered or gross soil should
be removed by brushing, scraping, shovelling or vacuum, etc. Wherever
possible, soil on floors and walls should be picked up and placed in suitable
waste containers rather than washed to drains using hoses.
Pre-rinse. Surfaces should be rinsed with low pressure cold water to remove
loosely adhered small debris. Hot water can be used for fatty soils, but too high a
temperature may coagulate proteins.
Cleaning. A selection of cleaning chemicals, temperature and mechanical
energy is applied to remove adhered soils.
Inter-rinse. Both soil detached by cleaning operations and cleaning chemical
residues should be removed from surfaces by rinsing with low pressure cold
water.
Disinfection. Chemical disinfectants (or occasionally heat) are applied to remove
and/or reduce the viability of remaining microorganisms to a level deemed to be
of no significant risk. In exceptional circumstances and only when light soiling is
to be removed, it may be appropriate to combine stages 5–7 by using a chemical
with both cleaning and antimicrobial properties (detergent-sanitiser).
Post-rinse. Disinfectant residues should be removed by rinsing away with low
pressure cold water of known potable quality. Some disinfectants, however, are
intended to be left on surfaces until the start of subsequent production periods
and are thus so formulated to be both surface-active and of low risk, in terms of
taint or toxicity, to foodstuffs.
Inter-production cycle conditions. A number of procedures may be undertaken,
including the removal of excess water and/or equipment drying, to prevent the
Cleaning and disinfection 415
growth of microorganisms on production contact surfaces in the period up until
the next production process. Alternatively, the processing area may be evacuated
and fogged with a suitable disinfectant.
Periodic practices. Periodic practices increase the degree of cleaning for
specific equipment or areas to return them to acceptable cleanliness levels. They
include weekly acidic cleans, weekend dismantling of equipment, cleaning and
disinfection of chillers and sanitation of surfaces, fixtures and fittings above two
metres.
A sanitation sequence should be established in a processing area to ensure that
the applied sanitation programme is capable of meeting its objectives and that
cleaning programmes, both periodic and for areas not cleaned daily, are
implemented on a routine basis. In particular, a sanitation sequence determines
the order in which the product contact surfaces of equipment and environmental
surfaces (walls, floors, drains etc.) are sanitised, such that once product contact
surfaces are disinfected, they should not be re-contaminated.
Based on industrial case studies, the following sanitation sequence for chilled
food production areas, has been demonstrated to be useful in controlling the
proliferation of undesirable microorganisms. The sequence must be performed at
a ’room’ level such that all environmental surfaces and equipment in the area are
cleaned at the same time. It is not acceptable to clean and disinfect one line and
then move onto the next and start the sequence again as this merely spreads
contamination around the room.
1. Remove gross soil from production equipment.
2. Remove gross soil from environmental surfaces.
3. Rinse down environmental surfaces (usually to a minimum of 2 m in height
for walls).
4. Rinse down equipment and flush to drain.
5. Clean environment surfaces, usually in the order of drains, walls then floors.
6. Rinse environmental surfaces.
7. Clean equipment.
8. Rinse equipment.
9. Disinfect equipment and rinse if required.
10. Fog (if required)
14.6 Evaluation of effectiveness of sanitation systems
Assessment of the effectiveness of the sanitation programme’s performance is
part of day-to-day hygiene testing and, as such, is linked to the factory
environmental sampling plan. The control of the environmental routes of
contamination is addressed via the development of a thorough risk analysis and
management strategy, typically undertaken as part of the factory HACCP study,
resulting in the development of the factory environmental sampling plan. The
416 Chilled foods
development of environmental sampling plans has recently been established by a
CCFRA industrial working party and is reported in Holah (1998).
Environmental sampling is directly linked with both process development
and product manufacture and as such, has three distinct phases;
1. process development to determine whether a contamination route is a risk
and assessing whether procedures put in place to control the risk identified
are working
2. routine hygiene assessment
3. troubleshooting to identify why products (or occasionally environmental
samples) may have a microbiological count that is out of specification or
may contain pathogens.
Related to chilled food manufacture, routine hygiene testing is concerned with
assessing the performance of the high-risk barrier systems in preventing
pathogen access during production and, after production has finished, the
performance of the sanitation programme.
Routine hygiene testing is an important aspect of due diligence and is used
for two purposes, monitoring to check sanitation process control, and
verification to assess sanitation programme success. Monitoring is a planned
sequence of observations or measurements to ensure that the control measures
within the sanitation programme are operating within specification and are
undertaken in a time frame that allows sanitation programme control.
Verification is the application of methods in a longer time frame to determine
compliance with the sanitation programme’s specification.
Monitoring the sanitation programme is via physical, sensory and rapid
chemical hygiene testing methods. Microbiological testing procedures are never
fast enough to be used for process monitoring. Physical tests are centred on the
critical control measures of the performance of sanitation programmes and
include, for example, measurement of detergent/disinfectant contact time; rinse
water, detergent and disinfectant temperatures; chemical concentrations; surface
coverage of applied chemicals; degree of mechanical or kinetic input; cleaning
equipment maintenance and chemical stock rotation.
Sensory evaluation is usually undertaken after each of the sanitation
programme stages and involves visual inspection of surfaces under good
lighting, smelling for product or offensive odours, and feeling for greasy or
encrusted surfaces. For some product soils, residues can be more clearly
observed by wiping the surface with paper tissues. Rapid hygiene methods are
defined as monitoring methods whose results are generated in a time frame
(usually regarded as within approximately 10 minutes) sufficiently quickly to
allow process control. Current methodology allows the quantification of
microorganisms (ATP), food soils (ATP, protein) or both (ATP). No technique
is presently available which will allow the detection of specific microbial types
within this time frame.
The most popular and established rapid hygiene monitoring technique is that
based on the detection of adenosine triphosphate (ATP) by bioluminescence and
Cleaning and disinfection 417
is usually referred to as ATP testing. ATP is present in all living organisms,
including microorganisms (microbial ATP), in a variety of foodstuffs and may
also be present as free ATP (usually referred to together as non-microbial ATP).
The bioluminescent detection system is based on the chemistry of the light
reaction emitted from the abdomen of the North American firefly Photinus
pyralis, in which light is produced by the reaction of luciferin and luciferase in
the presence of ATP. For each molecule of ATP present, one photon of light is
emitted which are then detected by a luminometer and recorded as relative light
units (RLU). The reaction is very rapid and results are available within seconds
of placing the sample to be quantified in the luminometer. The result, the
amount of light produced, is also directly related to the level of microbial and
non-microbial ATP present in the sample and is often referred to as the
‘hygienic’ status of the sample.
ATP has been successfully used to monitor the hygiene of surfaces for
approximately 15 years and many references are available in the literature citing
its proficiency and discussing its future potential e.g. Bautista et al. (1992),
Poulis et al. (1993), Bell et al.(1994), Griffiths et al. (1994), Hawronskyj and
Holah (1997). It is possible to differentiate between the measurement of
microbial and non-microbial ATP but for the vast majority of cases, the
measurement of total ATP (microbial and non-microbial) is preferred. As there
is more inherent ATP in foodstuffs than in microorganisms, the measurement of
total ATP is a more sensitive technique to determine remaining residues. Large
quantities of ATP present on a surface after cleaning and disinfection, regardless
of their source, is an indication of poor cleaning and thus contamination risk
(from microorganisms or materials that may support their growth).
Many food processors typically use the rapidity of ATP to allow monitoring
of the cleaning operation such that if a surface is not cleaned to a predetermined
level it can be recleaned prior to production. Similarly, pieces of kit can be
certified as being cleaned prior to use in processing environments where kit is
quickly recycled or when the manufacturing process has long production runs.
Some processors prefer to assess the hygiene level after the completion of both
the cleaning and disinfection phases whilst others monitor after the cleaning
phase and only go onto the disinfection phase if the surfaces have been
adequately cleaned.
Techniques have also been developed which use protein concentrations as
markers of surface contamination remaining after cleaning operations. As these
are dependent on chemical reactions, they are also rapid but their applicability is
perhaps less widespread as they can only be used if protein is a major part of the
food product processed. As with the ATP technique, a direct correlation between
the degree of protein remaining after a sanitation programme has been
completed and the number of microorganisms remaining as assessed by
traditional microbiological techniques, is not likely to be useful. They are
cheaper in use than ATP based systems as the end point of the tests is a visible
colour change rather than a signal which is interpreted by an instrument e.g.
light output measured by a luminometer.
418 Chilled foods
Protein hygiene tests were further developed and recently reintroduced by
Konica as the ‘Swab’ n’ Check’ hygiene monitoring kit. This assay detects the
presence of protein on a surface by an enhanced Biuret reaction, the end point of
which is a colour change from green through to purple. The surface to be
assessed is swabbed and the swab placed into a tube of resuspension fluid
containing the reagents necessary to activate the Biuret reaction. After ten
minutes any colour change is compared to a supplied colour card and the degree
of colour change used as an indication of the hygienic nature of the surface.
However, there is currently little published data on both the efficacy of this
system (Griffith et al. 1997) and the food-processing environments to which it is
best suited. Other manufacturers have also recently launched competing
products.
Verification of the performance of the sanitation programmes is usually
undertaken by microbiological methods in the chilled food industry, though ATP
levels are also used (especially in low risk). Microbiological sampling is
typically for the total number of viable microorganisms remaining after cleaning
and disinfection, i.e. total viable count (TVC), both as a measurement of the
ability of the sanitation programme to control all microorganisms and to
maximise microbial detection. Sampling targeted at specific pathogens or
spoilage organisms, which are thought to play a major role in the safety or
quality of the product, is undertaken to verify the performance of the sanitation
programme designed for their control. Microbiological assessments have also
been used to ensure compliance with external microbial standards, as a basis for
cleaning operatives’ bonus payments, in hygiene inspection and troubleshooting
exercises, and to optimise sanitation procedures.
Traditional microbiological techniques appropriate for food factory use
involving the removal or sampling of microorganisms from surfaces, and their
culture using standard agar plating methods have been reviewed by Holah
(1998). Microorganisms may be sampled via sterile cotton or alginate swabs and
sponges, after which the microorganisms are resuspended by vortex mixing or
dissolution into suitable recovery or transport media, or via water rinses for
larger enclosed areas (e.g. fillers). Representative dilutions are then incubated in
a range of microbial growth media, depending on which microorganisms are
being selected for, and incubated for 24–48 hours. Alternatively, microorgan-
isms may be sampled directly onto self-prepared or commercial (‘dip slides’)
agar contact plates.
The choice of sampling site will relate to risk assessment. Where there is the
potential for microorganisms remaining after (poor) cleaning and disinfection to,
via e.g. direct product contact, infect large quantities of product, these sources
would require sampling much more frequently than other sites which, whilst
they may be more likely to be contaminated, pose less of a direct risk to the
product. For example, it is more sensible, and gives more confidence, to sample
the points of the equipment that directly contact the product and that are difficult
to clean than to sample non-direct contact surfaces, e.g. underneath of the
equipment framework.
Cleaning and disinfection 419
In relation to microorganism numbers, it is difficult to suggest what is an
‘acceptable’ number of microorganisms remaining on a surface after cleaning
and disinfection as this is clearly dependent on the food product, process, ‘risk
area’ and degree of sanitation undertaken. A number of figures have been quoted
in the past (as total viable count per square decimeter) including 100 (Favero et
al. 1984), 540 (Thorpe and Barker 1987) and 1000 (Timperley and Lawson
1980) for dairies, canneries and general manufacturing respectively. The results
in Table 14.1 show that in chilled food production, sanitation programmes
should achieve levels of around 1000 microorganisms per swab, which on flat
surfaces approximately equates to a square decimeter. Expressing counts
arithmetically is always a problem, however, as single counts taken in areas
where cleaning has been inadequate (which may be in excess of 10
8
per swab)
produce an artificially high mean count, even over thousands of samples. It is
better, therefore, to express counts as log to the base 10, a technique that places
less emphasis on a relatively few high counts, and Table 14.1 shows that log
counts of approximately 1 should be obtained.
Because of the difficulty in setting external standards, it is best to set internal
standards as a measurement of what can be achieved by a given sanitation
programme. A typical approach would be to assess the level of microorganisms
or ATP present on a surface after a series of ten or so sanitation programmes in
which the sanitation programme is carefully controlled (i.e. detergent and
disinfectant concentrations are correct, contact times are adhered to, water
temperatures are checked, pressure hoses are set to specified pressures,
sanitation schedules are followed, etc.). The mean result will provide an
achievable standard (or standards if specific areas differ significantly in their
cleanability) which can be immediately used and can be reviewed as subsequent
data points are obtained in the future. A review of the standard would be
required if either the food product or process or the sanitation programme were
changed.
As part of the assessment of sanitation programmes, it is worthwhile looking
how the programme is performing over a defined time period (weekly, monthly,
quarterly etc.) as individual sample results are only an estimate of what is
happening at one specific time period. This may be to ensure that the programme
remains within control, to reduce the variation within the programme or, as
should be encouraged, to try and improve the programme’s performance. An
assessment of the performance of the programme with time, or trend analysis,
can be undertaken simply, by producing a graphical representation of the results
on a time basis, or can be undertaken from a statistical perspective using
Statistical Process Control (SPC) techniques as described by Harris and
Richardson (1996). Generally, graphical representation is the most widely used
approach, though SPC techniques should be encouraged for more rigorous
assessment of improvement in the programme’s performance.
420 Chilled foods
14.7 Management responsibilities
Senior management must take full responsibility for the successful operation of
the sanitation programme; ultimately, failures in the programme generally
reflect poor management. For the majority of chilled food processing operations,
the following is a guide to the responsibilities of senior management.
? Always seek to improve hygiene standards in line with the high-risk
philosophies adopted in Chapter 13. Hygiene has traditionally not had the
same research support as other areas of importance in food manufacture and
is thus a new and developing science. It is only relatively recently that new
concepts have been developed, based on scientific assessments, and
management must be flexible enough to try out and to encourage such
concepts when they emerge.
? Lead by example by being both always properly attired in food production
areas and (occasionally) present in production areas when sanitation is being
undertaken (usually in the early hours of the morning!)
? Provide the required equipment (including maintenance), the staffing levels
and the time to undertake the sanitation programme effectively. Cleaning
operatives must be a dedicated labour pool whose priority is to sanitation (i.e.
not production). Similarly, operatives should not join in the cleaning team as
an ‘introduction to production’.
? Management should be capable of giving praise when sanitation is
undertaken correctly, as well as discipline when it is not. In companies
where bonus systems have been employed based on microbiological
assessments of equipment after cleaning, results have indicated that hygiene
has generally been improved and bonuses are rarely missed.
? Appoint or nominate a manager to be responsible for the day-to-day
implementation of the sanitation programme.
The manager who assumes responsibility for the sanitation programme must
have technical hygiene expertise and has a range of job functions including the
following:
? the selection of a suitable chemical supplier
? the selection of sanitation chemicals, equipment and methodology
? the training of cleaning operatives
? the development of cleaning schedules
? the implementation of sanitation programme monitoring systems
? representation of hygiene issues to senior management.
Good chemical suppliers are able to do much more than simply supply
detergents and disinfectants. They should be chosen on their abilities to
undertake site hygiene audits, supply suitable chemical dosing and application
equipment, undertake operative training and help with the development of
cleaning schedules and sanitation monitoring and verification systems. Good
chemical companies respond quickly to their customers’ needs, periodically
Cleaning and disinfection 421
review their customers’ requirements and visit during sanitation periods to
ensure that their products are being used properly and are working satisfactorily.
The cleaning manager may also need to visit the chemical supplier’s site to audit
their quality systems.
Whilst in theory systems and/or chemicals could seem appropriate for the
required task, every factory, with its water supply, food products, equipment,
materials of construction and layout, etc., is unique. All sanitation chemicals,
equipment and methodology must, therefore, be proven in the processing
environment. New products and equipment are always being produced and a
good working relationship with hygiene suppliers is beneficial. Only
disinfectants that have been approved to the relevant European Standards
should be used.
The cleaning operatives’ job is both technical and potentially hazardous, and
all steps should be undertaken to ensure that sufficient training is given. By the
nature of the job, training is likely to be comprehensive and should include:
? a knowledge of basic food hygiene
? the importance of maintaining low/high-risk barriers during cleaning
? the implications to product safety/spoilage of poor sanitation practices
? an understanding of the basic function and use of sanitation chemicals and
equipment and of their sequence of operation
? a thorough knowledge of the safe handling of chemicals and their application
and the safe use of sanitation equipment.
For each piece of equipment or for each processing area, a cleaning or
sanitation schedule should be developed, preferably in a loose-leaf format so that
it can readily be updated and which should always be available for inspection by
cleaning operatives or auditors. The schedule must show clearly each stage of the
cleaning and disinfection process (diagrammatically if this would help), all
pertinent information on safety, and the key inspection points and how these
should be assessed. It is difficult to produce a list of requirements that should be
found in a cleaning schedule, but the following is a typical, non-exhaustive list:
? a description, hazard code, in-use concentration, method of make up, storage
conditions, location and amount to be drawn of all chemicals used
? type, use of, set parameters (pressure, nozzle type, etc.), maintenance and
location of sanitation equipment
? description of the equipment to be cleaned, need for fitters, need to
disconnect from services, dismantling and reassembly procedures
? full description of the cleaning process, its frequency and requirement for
periodic measures
? staff requirements and their responsibilities
? key points for assessment of the sanitation procedure and description of
evaluation procedures for programme monitoring and verification.
When new equipment is purchased or processing areas designed or
refurbished, insufficient attention is usually placed on sanitation requirements.
422 Chilled foods
Equipment or areas of poor hygienic design will be more expensive to clean
(and maintain) and may not be capable of being cleaned to an acceptable
standard in the time available. If improperly cleaned, adequate disinfection is
impossible and thus contamination will not be controlled. Hygiene management
must be strongly represented, thus ensuring that hygiene requirements are
considered alongside those of engineering, production and accounts, etc.
Three types of sanitation programme can be implemented by management
and each has its advantages and disadvantages: at the end of production,
production operatives clean their workstations and then (a), they form a cleaning
crew and undertake the sanitation programme; (b), a separate, dedicated
cleaning gang complete the sanitation programme; or (c) cleaning and
disinfection is undertaken by contract cleaners. Whilst each option will place
different demands on the food manufacturer, the principles as mentioned above
should always be incorporated and the sanitation programme effectively
managed.
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