PHYSICAL METHODS FOR KILLING MICROBES • Sterilization methods – Incineration – Autoclave – Dry heat oven – Filter sterilization – Ultra violet light – Gamma radiation
Dec 24, 2015
PHYSICAL METHODS FOR KILLING MICROBES
• Sterilization methods– Incineration– Autoclave– Dry heat oven – Filter sterilization– Ultra violet light– Gamma radiation
The direct flame represents a rapid sterilization method
Incineration
The autoclave uses moist heat and pressure
Boiling water involvesmoist heat
• This is not a reliable method for sterilization unless tyndallization is used.
• Why not?
Pasteurization does not sterilize
• It is used to kill unwanted or harmful microbes
• Why doesn’t it sterilize?
Hot-air (dry-heat) oven
Time and Temperature: 338F for 11/2 hours
Filter Sterilization
Filtration traps microorganisms
Ultraviolet light can be used to control microbial growth
UV light attacks the cell’s DNA
What are some disadvantages in the use of UV for sterilization?
The Ionizing and Electromagnetic Spectrum of Energies
Thymine Dimers of DNA form when exposed to UV light
Thymine Dimers
CHECK MOLES FOR THESE CHANGES
GAMMA RADIATION
A widely used method for sterilizing materials that would be adversely
altered by heat (plastics, lensed equip. heart-lung machines etc).
Logo for gamma radiationLook for this logo on those foods that have been treated with gamma
radiation, such as meats, and produce.
PRESERVATION METHODS
Drying (dehydration) Method
Salting Method
Low pH Method
Do these methods sterilize the food? Explain.
General Principles ofChemical Control
Resistance of microbes to chemical agents
Disinfectants
Killing Action of certain metals
Killing Action of Some Antiseptics