PHYSICAL METHODS FOR KILLING MICROBES Sterilization methods –Incineration –Autoclave –Dry heat...

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