Physical Methods of Microbial Control

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Physical Methods of Microbial Control

Radiation

Microwaves

nonionizing radiation

Subtopic

UV light

Ionizing radiation

carries more energy than nonionizing

gamma rays, X rays, high energy electron beams

Osmotic Pressure

yeasts and molds can grow

preservation of food

hypertonic

use of high conc of salts or sugars

Desiccation

bacterial endospores resistant

viruses generally resistant

water removed...growth stops...water back...growth continues

High Pressure

preserves flavor, colors and nutrient values

endospores are resistant

Filtration

spirochetes can make it through filters because they are flexible

membrane filters...industrial and lab use

HEPA filters..operating theaters and burn victim rooms

used to sterilize heat-sensitive materials

Heat

Low Temperatures

slow freezing more harmful to bacteria

ordinary refrigeration has bacteriostatic effect

Dry Heat Sterilization

hot-air sterilization: 170C for at leat 2 hours

flaming: sterilizing inoculation loop

kills by oxidation effects

Pasteurization

equivalent treatments: as temp increases, less time is needed to kill same number

ultra-high temperature treatments: 140C...milk in boxes

high temperature short time : at least 72C for only 15 seconds

phosphatase test...phosphates inactive when pasteurized

less effective in foods that are more viscous

thermoduric pathogens survive process

Moist Heat

autoclave

industrial autoclaves = retorts

15 psi will kill all but prions and their endospores in about 15 mins

higher the pressure the higher the temp

steam under pressure

boiling

bacterial endospores can survive more than 20 hours

hepatitis can survive up to 30 mins

about 10 minutes

fungi and spores

all most all viruses

kills vegetative bacterial paths.

kills by coag of proteins...egg white frying

decimal reduction time (DRT): time, in mins, in which 90% of bacteria at a given temp will be killed

thermal death time (TDT): minimal length of time it takes for all mo to be killed at a given temp

thermal death point (TDP): lowest temp at which all mo in a particular liquid suspension will be killed in 10 minutes

kills by denaturing enzymes...changes 3D shape