Cleaning and disinfecting in the food industry: theoretical and practical aspect


Cleaning is the net to make (a place or object) removing any dirt or anything detrimental to the cleanliness.

Disinfection is the elimination or the inhibition of microorganisms in a place, an object or on the external surface of the human body.

In food industry (food), cleaning and disinfection are designed to remove dirt and destroy the microorganisms present in the appliances and packaging. In some cases, these operations must be conducted on the products themselves contaminated by for earth, microbes, or residues of pesticides.

The results of these two operations are not exclusive of each other because if the cleaning operation will remove a number of waste, it will also achieve a certain level of elimination of microorganisms. This elimination can then be supplemented if necessary by a proper disinfection implementing a specific product. Commonly a detergent (eg alkaline) will be used simultaneously with a disinfectant (chlorine and derivative) in the form of alkaline chlorine Some formulations include even a quaternary ammonium or other product to increase the disinfecting power in a single operation for cleaning / disinfection.

Cleaning and disinfection operations are among the most important of the IAA and this for various reasons:

  • The quality of the finished product is often influenced by the tastes of foreigners due to microbial development. These developments are dependent on the residues of this product in the device or in a container after use, or from deposits that are formed during the processing of certain products such as beer, milk, ...
  • The ability to heat treatment is highly dependent on the initial population. Indeed, when sterilises pasteurizes or on a product by heat, time of treatment depends on the initial microbial load. It is much longer if this burden is not reduced by a preliminary cleaning. This increases the cost of treatment and may diminish the quality of the product.
  • The dirt may contain pathogenic microorganisms and, thus, constitute a source of contamination is extremely harmful to the food.
  • The presence of residues such as dried crusts or altered insects or their larvae, rodents or even in the packaged products can have a catastrophic influence on the opinion of the consumer.

Nature of contamination

Denotes dirt (or dirt) products are totally different. These products are components of food more or less degraded, or modified by heat, cold, humidity, light, oxygen and / or microorganisms.

These components may be more or less mixed with others: filter, yeasts or molds, plant debris or minerals, seeds of the atmosphere or made by staff.

In theory, a stain is characterized by the ratio of its water solubility and lipid solubility, and it is this characteristic that should be taken into account when choosing chemical decontamination agents. The stain is a complex organic matter, mineral matter and microbial germs. Each of these three families of compounds must be known in detail.

Organic compounds are: lipids, proteins and carbohydrates. The inorganic compounds can be divided into several categories which are based on their nature and power of elimination: The alkaline earth salts, silicates, oxalates and aluminates.

Microbial germs are classified into two categories: useful germs and harmful germs. When present simultaneously in the environment of the food product or the product itself, it is not possible in current practice, to make selective treatment, to control bacterial life in a product , we start by destroying everything and réensemence layers useful decimated.

Kinetics of the elimination of contamination

Between certain limits, often at the beginning of the elimination of dirt, the elimination of dirt behaves as a first order reaction. Ifmrepresents the mass of soil per unit area, we have:

Kinetics of the removal of dirt

The rate constant k is determined by several factors:

  • The nature of the support of the dirt: We know, for example a surface of polished stainless steel is easier to clean a rough surface or plastic. Wooden surfaces are extremely difficult to clean.
  • The nature and concentration of detergent: When using a dilute solution of caustic soda, the reaction of removing dirt becomes second order. However, this finding can be extended to other surfactants.
  • Temperature: Between broad intervals of temperatures, the rate constant follows the Arrhenius law, ie that we obtain a linear relationship on log (K) against T-1.
  • The Mechanics: The mechanical action during the passage of a fluid in a conduit, only becomes significant when the Reynolds number (Re) is greater than 25 000; beyond this value, the rate constant varies roughly as log (Re).

The mechanical action can be influenced by the presence of foam in which the action may be detrimental by preventing contact between the surface and the solution. The action of the foam may also be beneficial when the air is dispersed in the solution in motion, which improves the abrasive action, the latter can be improved by making advantage of suspended solids as elastic or rubber bullets, which are driven in the circuit.

This theoretical approach to the kinetics of cleaning is widely criticized because it does not reflect the experimental results and the methods used for measuring the speed of cleaning is inaccurate.

Regarding the chemical destruction of microorganisms, it is generally considered that the reaction is first order. If Nmis the number of cells in a given microorganism per Kg of product, we have:

Chemical destruction of microorganisms

In this case, the rate constant k is a function of the strain of microorganisms, the nature and concentration bactericidal agent, it is also strongly influenced by temperature and the composition of the environment in which the destruction takes place .

In practice, the problem is not chemically sterilize a suspension of microorganisms, but a surface that is possibly a deposit containing living microorganisms. In this situation, several interactions may exist: support, trust, solid, suspended matter, microorganisms, cleaning and disinfection. These interactions are extremely complex and it is very difficult to model.

Disinfection in depth of deposition, materials porous interstices of various joints, valves, etc.. is generally not possible by use of highly reactive body as halogens which the concentration drops sharply and fell to values at a depth sublétales very low. On the other hand when using products such as formaldehyde, protein deposits can be hardened on the surface and make their removal more difficult than ever without the formaldehyde concentration in the deposits is less than a truly bactericidal.

Finally, it should be noted that in general the nature of the cleaning agents and disinfecting that can be used depends mainly on the materials constituting the apparatus, the phenomena of corrosion still playing a decisive role.

Cleaning Products

Detergents are products whose solutions help to remove dirt or other foreign bodies contaminated surfaces. Until the 1940s, soap was the only detergent important. Today, there are many others.

Mode of action of cleaning products

Detergents are amphiphilic molecules: they have a polar head (hydrophilic) who loves the water and a tail apolar (hydrophobic), which pushes the water. This amphiphilic character which is behind the action of detergents.

Representation of the amphiphile

When you put a detergent in water, it feels that it is soluble in spite of its amphiphilic character. In fact, it is a grouping of detergent molecules in the form of micelles that remain suspended in water. In a micelle the parties polar (hydrophilic) head to the outside (in contact with water) and the parties apolar (hydrophobic) is moving inwards (in contact with other hydrophobic parts).


When agitated water containing a surfactant, hydrophobic soils (exp: oil, grease, ...) associated with the central part of the micelles due to their hydrophobic character. Thus, fouling are micelles in suspension while the remainder of the order of molecular size (100 to 200 angstroms). When rinsing, these micelles are driven by water and dirt are separated from their support.

However, the formation of micelles is observed until the critical micellar concentration (concentration at which the molecules form micelles). The detergent real action occurs that at concentrations of surfactant above the critical micellar concentration. For alkyls-aryl-sulfonate the critical micellar concentration is about 0.1%, but it is strongly influenced by temperature and the presence of salt, also inert, can significantly decrease the critical micellar concentration and therefore increase the detergent.

Cleaning Products


A surfactant is by definition a body able to modify significantly the properties of the surface or interface solutions. Broadly speaking, these bodies are called amphiphiles, ie have one or more polar groups and apolar hydrocarbon chain generally containing 10 to 20 carbon atoms.

One class generally surfactants according to the polar nature of the group:

  1. The anionic surfactants have a polar acid group, the main products of this type are:
    • Soaps or alkaline salts of fatty acid,
    • alcoylsulfates the primary and secondary
    • the alcoylaryl sulfonates.

    These products are excellent detergents, they are not bactericidal and, except for the soap, are not very sensitive to water hardness.

  2. Cationic surfactants are solubilized to a quaternary ammonium group or an ethoxylated amine. The former can be excellent bactericidal and the latter are of corrosion inhibitors in acidic media.
  3. Surfactants, anionic non-condensate are generally of ethylene oxide on alcoylphénoles or fatty alcohols. These products are excellent bactericidal detergent whose solubility is greater in cold than hot, and this solubility increases with the number of molecules of ethylene oxide. An offshoot of the chain solubilising can not make foam.
  4. The amphoteric surfactants are solubilized by both anionic and cationic groups and some of these products have a limited use as bactericides.

Other cleaning products

Strong alkalis are excellent detergents and bactericides. Caustic soda, for example, which also has virucidal and sporicidal action is used whenever the materials constituting the apparatus permit.

Strong acids are excellent detergents and bactericides. We use nitric acid, hydrochloric and phosphoric. Sulfuric acid passivated has excellent bactericidal, even against the spores.

Weak acids such as gluconic acid, citric Sulfamic do a cleaning action considerably lower than that of strong acids and their bactericidal action is practically nil, it is also alkaline salts whose action can in no way be compared to that of caustic soda.

The chelating agents set the alkaline earth cations in the form of non-ionisable complexes. It uses mainly polyphosphates, ethylene-diamine-tétracétate and gluconates or glucoheptonate.

Polyphosphates are salts of partial anhydrides of phosphoric acid with not only a chelating action, but an inhibitory action of precipitation occur even when only small proportion of the water hardness is chelated.

Chlorine generally regarded as a disinfectant also has qualities used for the removal by oxidation of proteins.

The products of disinfection

Mode of action

The bactericidal action of chemical agents may result from a change in permeability of the cell membrane, or a rupture of this membrane, action on certain enzymes or certain cellular proteins, by oxidation, d a reduction or hydrolysis of vital constituents, or of interference with essential substrates.

Some of these reactions are not selective, chlorine, for example, reacts as well on non-cellular oxidizable group on cellular constituents, the silver reacts on the SH-groups of compounds exocellulaires as well as those of the constituents of the cell. It follows that, in many cases, the concentration of bactericidal agent in the environment decreases with time, resulting in a decrease in the pace of destruction of microorganisms. In the case of highly reactive body, such as chlorine, are often in practice proportions sufficiently high concentration for a measurable free chlorine remains after reaction of the organic matter in the middle.

The products of disinfection

The choice of products for cleaning and disinfecting materials depends mainly constituting the apparatus, the phenomena of corrosion still playing a decisive role.

Some cleaning products already discussed above, have important bactericidal action. They include quaternary ammonium products, as well as strong acids and alkalis, they can be active even against microbial spores and viruses. When the material to their jobs, there is often no need to seek alternative in practice. The problem of choice of other bactericidal agents arises therefore that in cases where the materials do not support strong acids and strong alkalis, and when we want to improve sanitation and prevent reinfection after treatment.

Bactericidal agents are the most commonly used halogen in particular chlorine and hypochlorites and these products are active at concentrations of chlorine from a few ppm (parts per million). It also uses the product of co-crystallization of CLON and containing approximately 3% of active chlorine in the form relatively stable.

Chlorine and hypochlorites are sometimes replaced by chloramines or chlorine acids. All products are characterized by the group:-N-Cl

This group reacts to chlorine ions (eg HCl) providing active chlorine, the following reaction:

–N–Cl + HCl   —––›  –NH + Cl2

This body, whose action is similar to hypochlorites, have on them the advantage of greater stability during storage.

Chlorine and its derivatives are effective bactericidal agents to low pH and even neighboring neutral but highly reactive, and fugitive may give rise to significant corrosion.

Stainless steel 18/8 is particularly sensitive to chlorine, which gives rise to pitting corrosion in causing porosity disastrously affecting the ability to clean.

Chlorine also has the disadvantage of being incompatible with the surfactants with which it reacts during storage, which is why it was proposed long ago, the use of mixtures of iodine and agents Surface non-ionic (condensates of ethylene oxide). These products designated under the name "iodophors have a bactericidal and sporicidal energetic even at concentrations of a few ppm of free iodine at pH below 4.5.

Efficacy of disinfectants

Iodine trichloride ICl3 has the advantage of being compatible with anionic surfactants to be more stable, less corrosive and to be bactericidal at pH neighbors neutrality.

Also used as bactericidal agents, the silver ions, formaldehyde, hydrogen peroxide and peracids, ozone, the 3-5-4 'tribromosalicylanilide, SO2 and sulphates etc.

For sterilization of packaging, the use of concentrated solutions of hot hydrogen peroxide is widespread. It also uses peracetic acid, phosphoric acid and chlorine.

For disinfecting food products themselves has proposed the use of ethylene oxide mixture with an inert gas.

Sterilization temperature rise can be very effective in the case of apparatus specially designed for the sterilization by hot water or by steam condensation. In the latter case, the condensed water and air must be eliminated by effective traps placed wisely.

Practical realization of the cleaning and disinfection

Cleaning is the removal of remnants of food deposits, microorganisms, and foreign body, any insect, etc.. Under normal conditions, the removal of microorganisms and spores is not complete and the cleaning must be followed by disinfection.

A key problem is deciding whether to conduct the cleaning and disinfection in one step or in two separate and successive operations.

In general, two successive operations can achieve better results because all bactericidal agents are inhibited by the presence of soiling themselves. It was therefore better to remove impurities first and then sterilized. The nature of materials equipment and design they also influence the choice. The desired degree of sterility must also be taken into account if we can tolerate an infection from a few thousand cells per kg as in the case of pasteurized milk, you can easily opt for the combined operation than in the case of aseptic packaging.

When the pH of the product is less than 4.0 it is not necessary to destroy spores of Bacillus and Clostridium, and can therefore use the products highly effective quaternary ammonium and non-corrosive. As against that the product has a pH above 4.5 should most often use halogen.

Cleaning and disinfection of the pipes are made by pumping the best solutions to achieve sufficient turbulence, it should be noted that at equal speed, the Reynolds number varies as the inverse of the diameter of the pipe; any expansion corresponds to a reduction of turbulence necessary to obtain satisfactory results. It is also necessary to include in the circuit, the sterilization of holes in three-way valves by a judicious rotation and avoid any area where the Reynolds number is less than 6000.

Cleaning and disinfection of vessels and tanks can not generally be achieved by movement due to excessive volumes of cleaning solution and due to insufficient turbulence during the transition of these solutions.

The methods of implementation are:

  • A brush: This system is heavily dependent on the human factor and should be removed whenever possible.
  • Jet manual: The influence of the human factor is also notable that this system is an improvement over the previous system.
  • Jet hot: This is more effective than low-temperature processes, provided that the table is not only on raising the temperature to achieve the cleaning and disinfection.
  • Jet caused by jet operated turnstiles (Figure 3).
  • Jet from ball or cylinder perforated.
  • Jet from mechanically controlled turnstiles.
  • Jet foam: A product for cleaning and disinfection should be added a foaming agent that allows highly spread a layer of foam on the equipment. It is this foam allows for the desired time and then eliminate it by simple rinsing.

reaction turbine

It should be noted that in general, as the operations of cleaning, disinfection and rinsing are strongly influenced by the design and construction of equipment, a cylindrical tank with a vertical axis is for instance much easier to clean mechanically that a tank with elongated horizontal axis, the reverse was true at the time cleaning the brush.

Several constraints may prevent or complicate the cleaning and disinfection automatic and simultaneous. Figure 4 presents some examples of these defects.

circuit cleaning

Containers are usually cleaned and disinfected in a single operation. This is the case for glass bottles undergoing soakings injections and solutions to approximately 1% NaOH to 70 ° C. This solution is generally added possibly a bactericidal agent.

Cleaning and disinfection of food products are usually made by passing through rotary devices where they are subjected to jets of detergent solutions and bactericides.

In industry the production of metabolites, fermenters are usually scheduled for automatic cleaning and circulation jets and sterilization under pressure of water vapor.

Rinsing is the removal of detergents and bactericides with water. The problem that is opposed to optimize this operation by reducing the volume of water consumed while removing traces of detergent and disinfectant. The current trend in the world, after the use of cleaning agents and adequate sanitation, not to rinse to avoid reinfection. Tolerances for remains very low indeed of these agents in food treaties have been published by the Food and Drug Administration.

Steps of cleaning and disinfection

Cleaning and disinfection can limit include the following steps:

  • Rinse;
  • Alkaline cleaning;
  • Intermediate rinsing;
  • Cleaning acid;
  • Intermediate rinsing;
  • Disinfection;
  • Final rinse.

Such a process is lengthy, costly and result in the formation of diluted sewage in considerable quantities. It is therefore important to do otherwise in order to reduce the disadvantages of this method while maintaining the same level of effectiveness.

Within the limits of the possible phases corresponding to the alkaline and acid cleaning can be conducted in one step using a product that eliminates both the organic and mineral stains. Thus, the process of cleaning and disinfection in 7 steps can be achieved in 5 steps:

  • Rinse;
  • Cleaning by a chemical agent;
  • Intermediate rinsing;
  • Disinfection by a chemical agent;
  • Final rinse.

Similarly, the phases of cleaning and disinfection may in some cases, be performed simultaneously. Foaming technology that ensures a contact time longer between detergents / disinfectants and the surfaces to be treated is often used. In this case, the process of cleaning and disinfection is conducted in 3 steps:

  • Rinse;
  • Cleaning and disinfection with a chemical agent;
  • Final rinse.

Cleaning and disinfection in 3 stages allows for a considerable gain in time, energy, labor and water. However, this process is only effective if the degree of contamination is at a relatively low level.

Frequency of cleaning and disinfection

Each type of manufacturing and / or equipment required is determined that the number of times the cleaning and disinfection will be necessary, within a period of time. The frequency of operation depends on the nature of the food product being implemented and technology transformation.

Regarding the frequency of cleaning, it can occur after several hours in the case of sterilization of milk in exchange or when the concentration of some residues. Very often, the cleaning takes place every day, it is in the meat industry in canning, baking or in stations bottling beverages. Sometimes the cleaning takes place each week, for instance in margarinerie. Finally, to the fermentation tanks or storage tanks, the intervals can be even more important.

As regards sanitation, the best way to determine the frequency of operation is to conduct a microbiological control to determine the evolution of the microbial flora as a function of time. This will deduct the time at which it must disinfect.

Control of cleaning and disinfection

It is not enough to choose a program of cleaning and disinfection and to apply, but we must also ensure its effectiveness. This is assessed following pre-established controls that allow one hand to ensure that the program of cleaning and disinfection is effectively implemented and secondly to ensure that it is effective.

Control of cleaning and disinfection is achieved in two ways: The first is to follow-up work and visual inspection to ensure the cleanliness of premises, machinery and utensils, and the second is to achieve the microbiological tests to ensure that the program of cleaning and disinfection is still effective.

After cleaning and disinfection, the microbial load of the surfaces is estimated by scanning the surface to be analyzed using a sterile swab which is then transferred in sterile distilled water for dilution. The seeds are dispersed using a Vortex mixer and the counting is done after seeding the culture medium and incubation at a given temperature depending on the type of germs sought.

Another technique, widely used in food industry, based on the use of blades gélosées. These are thin layers of culture medium on a rigid plastic or flexible. They are applied either directly to the surface to be analyzed indirectly after swab and put into suspension of flora collected by the swab. Dipping the blade in the liquid gélosée suspension will count flora therein.

Whatever the method used, it should be noted that only a certain proportion (approx. 40%) of the microflora present on the surface analyzed is levied. The operating results is primarily by comparing two different surfaces and studying the evolution of results over time to detect the development of germs on a given surface. In which case it is necessary to change program disinfectant and cleaning and disinfection, at least temporarily until the disappearance of these germs.

Techniques for microbiological analysis by swabbing or by gélosées blades have the advantage of being selective and precise if you want. However, they are slow and can not make a decision timely. The use of the ATPmetry for assessing the effectiveness of cleaning and disinfection as an alternative to these methods and has the advantage that it can quickly identify sensitive areas in terms of cleaning and disinfection.

The ATPmetry is a technique of instant mix of the ATP (adenosine triphosphate), a molecule of energy storage in living organisms. The technique, based on the principle of bioluminescence, is an enzymatic reaction indicating a quantity of ATP in the amount of light. Applied to the cleaning disinfection, it enables the detection of food residues and microbial development.


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