MEDI1000 Study Guide - Final Guide: Pasteurization, Food Spoilage, Louis Pasteur
16 Jun 2018
School
Department
Course
Professor
Foundations of Biomedical Science
Microbial Control
Control of Microbial Growth
Cleaning
-Removal of visible soils such as food residues, dust, dirt, corrosion, scale and grease from
a surface
-Microorganisms are removed but not killed
-Often achieved with water and detergent
Sanitisation
-A process that destroys various microorganisms, reducing viable numbers on clean
surfaces to meet product quality and public health standards
-Sanitisers are usually not effective in the presence of organic residues and detergents
-Often achieved with moist heat (steam) or chemicals (chlorine)
Disinfection
-Removal of pathogens only
Sterilisation
-Removal of all microbes including bacterial spores
Disinfection
-The process of killing pathogenic organisms or rendering them inert
-Germacide
-An agent that kills pathogenic microorganisms
-Disinfectant
-A substance that removes or causes the destruction of harmful microbes (not usually
spores), from inanimate objects
-Antiseptic
-A disinfectant for animate areas
Methods of Disinfection
Physical Methods for inanimate objects
-Heat (Pasteurisation)
-Typically in the range of 60 -800C for a few minutes to kill pathogens and to
destroy most other bacteria that cause food spoilage (i.e. preservation, to increase
shelf life)
-Radiation
-Ultra-violet (UV) radiation (usually non-ionising)
-Infra red radiation (non-ionising)
-Ionizing radiation (has enough energy to liberate an electron from an atom)
-Heat (Boiling)
Chemical Methods (solutions) for inanimate and animate sites!
Disinfection - Pasteurisation
-Developed by Louis Pasteur - mid 1800s to prevent spoilage of wine
-Low temp, Long time (LTLT) = 63 ̊C, 30 min
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-High temp, Short time (HTST) = 72 ̊C, 15 sec
-Used for heat sensitive equipment & foods
-Raw milk, juices, wine
-Destroys key pathogens in raw milk such as:
-Mycobacterium tuberculosis
-Salmonella enterica subsp. enterica Typhi or Salmonella Typhi for short
-Reduces spoilage bacteria
-Extends shelf life
Pattern of Microbial Death: Typical survivor curve
-Heat is applied to a microorganism at a
constant lethal temperature
-Rate of destruction is plotted where log10 of
survivors is linear with time of heating at a
constant temperature
-The ‘decimal reduction time’ (D) is the
time (minutes) for the survivors to be
destroyed by one log cycle which
represents 90% of the initial population
-(e.g. left. the test organism would have a (D)
value of D67 = 5.0 minutes)
Calculate the D value
-Using the above graph, calculate the
D value for the unknown test
organism at 50°C, 60°C and 70°C
respectively?
Disinfection - Radiation
Ultra Violet (UV)
-Bactericidal wavelength 200-295nm
-Damages proteins & nucleic acid
-Low penetrating power
-Moderate exposure time (20-30 mins
for a fume hood)
-Reduction of microbes in air, water &
on surfaces
Non-ionising - infra-red
Ionising
-Electron beam (most effective)
-Gamma-rays (needs lead shielding)
- X-rays
-Damage DNA by disrupting chemical bonds in
cells
-Uses: plastics, oils, food and greases etc
-Prolonged exposure = sterilisation achievable !
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Disinfection - Chemicals
Some for animate use and some only for inanimate objects
Modes of Action
-Protein coagulation/denaturation
-Disruption of cell membrane
-Chemical antagonism (inactivation of enzymes)
Types of Chemical Disinfectants
-Protein coagulation/denaturation
-Alcohols
-Aldehydes
-Halogens (iodine)
-Heavy metals & their compounds
-Phenols & phenolic compounds
-Disruption of cell membrane
-Surface active agents
-Halogens (chlorine)
-Chlorhexidine
-Phenols
-Chemical antagonism (inactivation of enzymes)
-Metals
Alcohols
-50-70% (70% - optimal)
-Ethanol and isopropanol
-Skin antiseptic and surface disinfection of objects
-Disadvantages:
-Many organisms require lengthy exposure for it to be effective • Low penetrating
power
-Inactivated by organic substances
-Low activity against spores & non-enveloped viruses
Aldehydes
-Formaldehyde & gluteraldehyde
-Disinfectants for objects only
-Advantages
-Non-corrosive to metals
-Disadvantages
-Both are tissue fixatives (i.e. rapidly kill and preserve cells)
-Strict safety precautions including; gloves, masks, glasses
Iodine (Halogen)
-Effective against bacteria, fungi, some endospores and many viruses
-Iodine tincture (iodine + alcohol)
-Povidone-iodine (iodophor)
-Iodine released slowly, good residual antiseptic activity – Povidone-iodine (iodophor) +
detergent
-(Betadine)
-Antiseptic for wounds
-Good for treatment of small wounds and infections
-Pre-op. skin disinfection
3
Document Summary
Removal of visible soils such as food residues, dust, dirt, corrosion, scale and grease from a surface. A process that destroys various microorganisms, reducing viable numbers on clean surfaces to meet product quality and public health standards. Sanitisers are usually not effective in the presence of organic residues and detergents. Often achieved with moist heat (steam) or chemicals (chlorine) Removal of all microbes including bacterial spores. The process of killing pathogenic organisms or rendering them inert. A substance that removes or causes the destruction of harmful microbes (not usually spores), from inanimate objects. Typically in the range of 60 -800c for a few minutes to kill pathogens and to destroy most other bacteria that cause food spoilage (i. e. preservation, to increase shelf life) Ionizing radiation (has enough energy to liberate an electron from an atom) Chemical methods (solutions) for inanimate and animate sites. Developed by louis pasteur - mid 1800s to prevent spoilage of wine.
