Biol 2460 Chap 13.2 - Using Physical Methods to Control Microorganisms

What is Heat sterilization?

• Oldest and most common

• Alters membranes and/or denatures proteins

What is Thermal death point?

lowest temp that will kill in 10 min.

What is Thermal death time?

length of time to kill at a certain temperature

What is Dry heat?

aka incineration; direct application of high heat (>250C)

What are examples of Dry heat applicators?

• Bunsen burner

• Bacteria incinerator

What is Moist heat?

application of high-temperature liquid/vapor

Why is Moist heat beneficial?

b/c penetrates cells better than dry

What is an example of a Moist heat applicator?

autoclave

How does the Autoclave function?

raises the temperature of water above boiling point (~121C) by raising pressure to 15 psi

What does the Autoclave kill?

viruses & endospores

What are the 2 main types of Autoclaves?

gravity & prevacuum

How does a Gravity autoclave work?

uses steam to push out air

How does a Prevacuum autoclave work?

vacuums out air first

What is Pasteurization?

“flash” heating foods to kill most microbes

How does High-Temp short time pasteurization work?

milk heated at 72 C for 15 sec, then bottled and refrigerated

How does Ultra-High-Temp pasteurization work?

milk heated at 138 C for 2 or more seconds, then sealed in an airtight container for up to 90 days without refrigeration

Is Refrigeration/Freezing sterilization or static?

static

What does Refrigeration/Freezing do to a cell?

slows metabolism but will grow when temps are raised

What are Ultra low temps(-80 C) used for?

used for preservation

What is Pascalization?

high pressure is used in the food industry to kill microbes

What is Desiccation?

drying or dehydration

What are examples of Desiccated foods?

raisins, prunes, jerky

What is Lyophilization?

freeze-drying; rapid freezing then placed under vacuum

What is used to lower Water activity of foods/materials?

salt or sugars

What does Ionizing radiation do to the cell?

enters into cells and disrupts molecular structures such as DNA

What are examples of Ionizing radiators?

x-ray and gamma rays

What does Non-ionizing radiation do to the cell?

does not penetrate glass, plastics, etc. but can damage cells w/ direct exposure

What is an example of an Non-ionizing radiator?

UV irradiation - forms thymine dimers in DNA causing lethal mutations

What is Sonication?

high frequency sound waves to disrupt cell structure

What does Sonication do to the cell?

causes bubbles to form inside cells and induce lysis

What is Membrane filtration?

removes microbes from liquid samples with filters with a pore size of 0.2 μm

What is Air commonly filtered through?

high-efficiency particulate air (HEPA) filters