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  3. Aston University, Birmingham (Aston)
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  5. Clinical and food microbiology BM6CFM (BM6CFM)

Lecture notes

CLEANING AND DISINFECTION
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• Aim – To study cleaning & disinfection practice in food hygiene and methods for assessing cleaning efficacy. • Objectives – Following this lecture you should be able to: • Explain the difference between cleaning & disinfection. • Define the terminology used in cleaning & disinfec...

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  • August 27, 2024
  • 11
  • 2023/2024
  • Lecture notes
  • Dr jonathan cox
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Cleaning and disinfection.

• Aim
– To study cleaning & disinfection practice in food hygiene and methods for
assessing cleaning efficacy.
• Objectives
– Following this lecture you should be able to:
• Explain the difference between cleaning & disinfection.
• Define the terminology used in cleaning & disinfection.
• Identify the strengths and limitations of a variety of cleaning and
disinfection agents.
• Describe methods available for the assessment of cleaning efficacy.




Control of microbial growth.
• Cleaning
– Remove residual food soil
• Thermal
• Kinetic
• Chemical
• Disinfection
– Microorganism

CLEANING- the main thing that we are doing when we are cleaning is removing debris and
residual food. This is sometimes referred to as soil or organic matter.
When washing up this is what we are doing.
The thermal aspect is there when we use hot water, the kinetic aspect is when you are
physically removing the dirt such as with a sponge. The chemical aspect is the fairy liquid,
which helps to remove the residual food and particular things that are fatty, such as oil.
Disinfection, such as on kitchen surfaces, this is targeting microorganisms and inhibiting
them or removing them from surfaces.
These two things are important in cleaning and disinfection in the food industry.

Surface active agents.
• Surfactants
– Soaps
– Detergents
• Emulsification

Surfactants- classic fairy liquid is a surfactant. It is a detergent.
We also have soaps, they are not just used in a food-based environment, they can be used
in the bathroom as well.
Soaps are based on animal fats.
Detergents and soaps emulsify fats throughout a water-based liquid.

, The detergents have molecules which have a hydrophilic head, this is water loving and a
hydrophobic tail, which is water repelling. This molecule forms the structure of a micelle.
When we mix the water based solutions and the oil based solutions or fats together, we get
a formation where the oil is contained inside the structures and this means that we can
emulsify the fat throughout the water or the liquid and we are able to remove those much
easier.
This is the first stage of cleaning.

Cleaning terminology.
• Detergents
– Anionic (-ve charge)
– Cationic (+ve charge)
– Non-ionic
– Amphoteric
• Charge is altered by the pH
• Abrasives
– Scouring Powders
• Sequesterants
– NaCl

Detergents tend to say at the back of them if they are made of anionic and cationic
surfactants.
Anionic surfactants or detergents, have a negative charge and they have a negative charge
in solution.
Cationic surfactants, have activity against microogranisms, they have a positive charge, so
they are active against the negative charge on the outside of the microorganisms. This is
how they have their antimicrobial activity.
We also have non-ionic surfactants; these do not have a charge and at the back of
detergents there is usually a percentage of anionic or cationic. And the other percentage
may say that it is made out of non-ionic surfactants. These do not have a charge and they
make up the rest of the product, they are a bulking agent and are acting as detergents.
The PH is important in the environment, anionic and cationic, only have their charges in
solution.
If we move outside of the solution, they loose their charge and they loose their activity. In
particular, the cationic surfactants.
There are also amphoteric surfactants, this is where they are depending on the Ph, the
conditions that are in the solution, they can be either positively or negatively charged.
Abrasives- some cleaning solutions have a physical aspect to them; these may include
scouring powders. It has a texture to it which is helpful in removing debris from surfaces.
Sequestrants- in dishwashers you separately put in detergent and salt. The salt is for
sequestering the minerals that are in the water, that can inactivate some of the surfactants
so they are not going to be able to do their job? They are not antimicrobial in the way that
they work, but they help to make sure that the other products that are in cleaning agents
are able to be antimicrobial.
Charge is important in order for them to be active.
It is not always a good idea to use different detergents or surfactants or cleaning products,
because this can lead to a problem with compatibility.

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