Physical Methods of Microbial Control

kills by denaturing enzymes...changes 3D shape

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

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

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

Moist Heat

kills by coag of proteins...egg white frying

boiling

kills vegetative bacterial paths.

all most all viruses

fungi and spores

about 10 minutes

hepatitis can survive up to 30 mins

bacterial endospores can survive more than 20 hours

autoclave

steam under pressure

higher the pressure the higher the temp

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

industrial autoclaves = retorts

Pasteurization

thermoduric pathogens survive process

less effective in foods that are more viscous

phosphatase test...phosphates inactive when pasteurized

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

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

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

Dry Heat Sterilization

kills by oxidation effects

flaming: sterilizing inoculation loop

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

Low Temperatures

ordinary refrigeration has bacteriostatic effect

slow freezing more harmful to bacteria

used to sterilize heat-sensitive materials

HEPA filters..operating theaters and burn victim rooms

membrane filters...industrial and lab use

spirochetes can make it through filters because they are flexible

endospores are resistant

preserves flavor, colors and nutrient values

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

viruses generally resistant

bacterial endospores resistant

use of high conc of salts or sugars

hypertonic

preservation of food

yeasts and molds can grow

Ionizing radiation

gamma rays, X rays, high energy electron beams

carries more energy than nonionizing

nonionizing radiation

UV light

Subtopic

Microwaves