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Cleaning and disinfection agents - module 3

This page provides a detailed discussion on the application and composition of cleaning and disinfection agents, and their role in industrial cleaning in the food industry. We recommend to study the slides presentation of the module first, as it provides the basics on cleaning and disinfection agents. For students and apprentices, the presentation is available as a PDF file. Teachers should have a look at the summary of didactical components before downloading the original PowerPoint presentation from the restricted area. When you have used the module, we would appreciate your feedback submitted in the online evaluation form. Filling in the module evaluation form will help to improve the quality of the training course. The advanced learners will find on this page a detailed discussion on the chemistry, and the principles of composing cleaning and disinfectant solutions.

Definitions

Cleaning agents

Cleaning agents are chemical substances in an aqueous solution to improve soil removal. Their tasks are manifold and can not be achieved by a single substance. Many cleaning agents are based on an aqueous solution with water, but not necessarily all cleaning agents may contain water, as organic solvents for the removal of fats, oil, bitumen, only contain small amounts of water. The cleaning agent solution is one factor for soil removal, in combination with time, temperature, and mechanical forces. The general requirements on cleaning agents are to be non-toxic, environmentally friendly, non-residual, non-corrosive, and to have a long storing period.

One of the most important tasks is to aid wetting of surfaces and pores and to allow a complete penetration of pores with water. Another is to weaken the bonds between soil and surface, to release the soil from the surface, and to keep it dispersed or dissolved in the solution (not allowing re-deposition onto the surface). Additionally, substances are added to mediate reactions with inorganic substances that cause mineral precipitation (water hardness), and reactions between surfactants and food soils. Due to their pH, cleaning agent can be categorized into alkaline (pH 7-12), neutral (app. pH 7), and acidic (pH 1-7) cleaners.

Composition of cleaning agents

An aqueous cleaning agent solution is commonly composed by water, surfactants, inorganic alkali, inorganic or organic acids, water softeners, and other substances. Other substances may be enzymes, scents, dyes, oxidants, or reductives. In order to fulfil the general requirements, a basic cleaner for the food industry would contain the components:

Cleaning properties of alkaline substances

Alkaline components like sodium hydroxide (NaOH) and soda (Na2CO3) do have the properties of soaking and denaturising proteins efficiently, and thus enable an easy removal of protein residues. They are however not able to emulsify fatty acids. Soda has a similar effect as free alkaline solutions, but is generally weaker.

Sodium orthophosphates (e.g. tri-. tetra, or pentasodium-phosphates) form a complex with calcium and magnesium ions, thus preventing precipitation of non-soluble salts. Such polyphosphates do have two important effects, firstly to avoid formation of sharp-edged calcite crystals, and secondly to dissolve precipitated protein residues bridged by calcium and magnesium ions.

Another important group of alkaline substances is represented by the different types of silicates which form micelles to prevent sedimentation of hydrophilic soil. Additionally, silicates prevent material-dependent corrosion. Alkaline substances generally show good cleaning properties for organic, especially protein soils.

Cleaning properties of acid substances

Acid substances do have good cleaning properties for mineral soils, which can not be removed by alkaline substances. The acid substance reacts with non-soluble carbonates under formation of water soluble carbonate acid. The acidic substances may be nitric acid (HNO3), sulphuric acid (H2SO4), or hydrochloric acid (HCl), which are characterised by their strong potential to release their hydrogenous ion (H+). Strong acids dissociate to a higher extent than weak acids (1-20% in contrast to 0,1-1%), and the strength of the acid is described in the dissociation rate (dissociation constant K). The higher the K value, the better it’s strength towards mineral depositions.

Depending on the pH, a cleaning agent sometimes is denoted as strong acidic (pH 0-2), or weak acidic (pH 3-4). Although the proton is the demineralising agent, it also causes corrosion at a number of materials, so that the use of acids always is a compromise between demineralisation power and corrosion power. Often, anti corrosive agents are added to acidic compounds which will protect the cleaned surface against attachment by the corrosive hydrogenous ion.

Cleaning properties neutral substances

The most neutral cleaning substances belong to the group of surfactants, a word that has been derived from surface active agent. Surfactants are wetting agents that lower the surface tension of a liquid, allowing easier spreading of a cleaning solution into pores and small lumen. The surfactant must be able to generate a surface tension of the aqueous solution which is lower than the surface tension of the foodstuffs. One of the most important tasks is to reduce the surface energy between water and greasy or oily substances, so that the oily substance easily can disperse in an aqueous solution and carried away.

Many surfactants will form aggregates, so called micelles beyond a certain concentration (figure 1). When micelles are present in water, their tails form a core that can encapsulate an oil droplet, and their heads form an outer shell that maintains favourable contact with water (figure 2). Reduction of surface tension occurs when surfactants form a monolayer, as shown in figure 3.

Foam occurs when air is encapsulated by two layers surfactants with a liquid layer in between.

Surfactants are classified by the charge of their hydrophilic heads, which might be non ionic (no charge), anionic (negatively charged), cationic (positively charged), or ampholytic (both, negatively and positively charged).

Water softeners

Water softeners are substances that bind to calcium and magnesium ions by a process called chelatation. Sodium triphosphate was the dominating water softener until the effect of eutrofication could be related to the presence of phosphate in rivers and lakes. Sodium triphosphate has been replaced by EDTA and phosphonates.

Other substances

One of the most important additional substances are foam inhibiting substances, such as alkylene oxide derivates. Such substances are important for instance in cleaning of bottles. Enzymes such as proteases (protein digesting enzymes) and amylases (carbohydrate digesting enzymes) are getting more and more important and may be a main components in the next generation's cleaning agents.

Composition of disinfection agents

Most disinfecting agents are composed by a number of active substances, which all have a specific spectrum of action. Commonly used active ingredients of disinfectants are alcohols, aldehydes (formaldehyde, glutardialdehyde), chlorine releasing compounds, peroxy compounds, or quaternary compounds. Some well known characteristics of active agents are listed in the table below.

Alcoholic compounds are preferentially used in hand disinfection products. They are characterised by rapid onset of action and favourable properties in terms of toxicology. Due to its flammability, only small volumes of alcoholic spray disinfectants (max 50 ml/m2) can be applied for surface disinfection procedures. Aldehydes do have a very broad spectrum of action in combination with a good material tolerance. However, because they may cause allergic reactions and there are irritant to mucosa, aldehydes should be replaced by other substances. Chlorine is a well known substance from the group of halogen compounds with a broad spectrum of action, but with only a limited range of application due to corrosiveness towards a number of materials. It is primarily used for disinfection of drinking water. Oxidants do have similar properties as aldehydes and are widely used for disinfection of instruments in hospitals as well as for the disinfection of linen.

A very interesting group from the cleaner’s point of view are surface active substances which comprise a combination of cleaning and disinfecting properties. They are non-odorous and gentle to surfaces and widely applied for disinfection in kitchens and the food industry. Due to a low tolerance against protein residues, the surfaces must be really clean prior to disinfection. In addition, water hardness must be kept low to keep for an efficient use of this type of compounds. Surfaces disinfected with quaternary compounds must be rinsed properly, otherwise sticky residues will remain on surfaces.

Choice of disinfectant

The choice of active ingredient often depends on the susceptibility of the surface, as chlorine is known to damage plastics. There is no general rule for the exposure time of a disinfectant, as it depends on the type of active ingredient and the concentration of ingredients (see DVG list). Alcohols for instance allow shorter exposure times than quaternary ammonia compounds. Many products are designed  for exposure times of 5-15 minutes, if applied in original concentration. The exposure time of disinfectants however is massively extended when it gets in contact with remaining water. Conversely, one should never apply a disinfectant at concentration higher than recommended, as many disinfectants need a certain amount of water to in order to penetrate cells.

Requirements on products for surface disinfection

One will choose the type of disinfectant depending on the microorganisms that are expected to be present. The type and strength of disinfectants is classified by an international product code ranging from class A products for easy to kill organisms to class-D products for extremely heat resistant spores.

Disinfection in food areas

Class A and B products are generally sufficient for disinfection purposes in food establishments as living bacteria, as well as many viruses (Hepatitis, SARS, Norwalk) are inactivated by such measures. We want to point out hat only tested and approved disinfectants should be applied. Lists with approved disinfectants are available from your national associations for agriculture and food hygiene. In Germany for instance, the foundation “Deutsche Veterinärmedizinische Gesellschaft” (DVG) issues a national list of tested and certified disinfectant. Other disinfectants may be applied, provided they have been tested with procedures equivalent in to the standards applied by national health and food hygiene organisations. In Germany, that would be the VAH, DGHM, and DVG test standards. In the event of epidemics, local health authorities can mandate special disinfection measures. In that case, only by the German Robert Koch Institute (RKI) listed disinfectants may be used.

An important pre-requisite for disinfection measures is cleanliness. This is because microorganisms are protected by soil and substances produced by the microorganisms themselves (biofilms). Presence of organic material, like blood and mucus will hamper disinfectants from attacking microorganisms. Some disinfectants are also inactivated by soaps. Hence, thorough rinsing must be conducted prior to application of disinfectants.