Lecture Midterm II

Question 1

Name 4 methods of preserving food

Answer 1

1. Refrigeration/freezing
2. Desiccation
3. Lyophilization
4. Osmotic pressure (sugar/salt)

Question 2

2 advantages and 2 disadvantages of membrane filtration

Answer 2

Advantages:
1. Fast, relatively inexpensive.
2. Useful for materials destroyed by heat.
Disadvantages
1. Enzymes and viruses not inactivated
2. May absorb some material, low recovery

Question 3

What is the pore size at which the filtrate is considered “sterile?”

Answer 3

0.22 um

Question 4

Define ionizing radiation

Answer 4

Radiation that carries enough energy to free electrons from atoms or molecules, thereby ionizing them. Wavelength < 1 nm.

Question 5

What are the effects of ionizing radiation?

Answer 5

Ions disrupt hydrogen bonding, oxidize double covalent bonds, and create highly reactive hydroxyl radicals. These ions in turn denature other molecules, particularly DNA, causing fatal mutations and cell death.

Question 6

Three examples of ionizing radiation

Answer 6

Electron beams
Gamma rays
X-rays

Question 7

Electron beam characteristics and uses

Answer 7

Effective at killing microbes, but poor penetration.

Uses: sterilize spices, meats, microbiological plastic ware, medical, dental supplies.

Question 8

Gamma ray characteristics and uses

Answer 8

Penetrate well, but takes hours to kill

Uses: sterilize spices, meats, fresh fruits and vegetables.

Question 9

X-ray characteristics and uses

Answer 9

Travel the farthest through matter, but have less energy than gamma rays and require a prohibitive amount of time to make them practical for microbial control.

Question 10

Define non-ionizing radiation

Answer 10

Electromagnetic radiation with a wavelength > 1 nm does not have enough energy to force electrons out of orbit.

However, such radiation does contain enough energy to excite electrons and cause them to make new covalent bonds, which can affect the three-dimensional structure of proteins and nucleic acids.

Question 11

Two examples of non-ionizing radiation used in microbial control

Answer 11

UV light

Microwave

Question 12

UV light characteristics and uses

Answer 12

• Crosslinks DNA (dimers), oxidizes proteins
• Not penetrating, therefore limited usefulness
• Used mostly for sanitizing surfaces, air, or water

Question 13

Microwave characteristics and uses

Answer 13

• In the presence of water, can kill microbes

- Cannot sterilize dry items, and endospores can be resistant

Question 14

Name 9 chemical methods of microbial control

Answer 14

• Phenols
• Alcohols
• Halogens
• Oxidizing agents
• Surfactants
• Heavy metals
• Aldehydes
• Gaseous agents
• Antimicrobics

Question 15

Phenolics

• mode of action
• uses
• example

Answer 15

• Denature proteins and damage plasma membranes. Effective in the presence of organic material.
• Healthcare, laboratories, households.
• Triclosan

Question 16

Alcohols

• mode of action
• uses
• example

Answer 16

• Dissolve membranes and denature proteins (requires water)
• Antiseptics. Evaporate quickly.
• Ethanol, Isopropanol

Question 17

Halogens

• mode of action
• uses
• example

Answer 17

• Probably by oxidizing cell components
• Chlorine: bleach, swimming pools, water treatment
• Bromine: hot tubs
• Iodine: betadine

Question 18

Oxidizing agents

• mode of action
• uses
• example

Answer 18

• Kill by oxidizing proteins/nucleic acids
• Hydrogen peroxide: disinfect/sterilize surfaces
• Ozone: drinking water
• Peracetic acid: sporocide to sterilize equipment

Question 19

Surfactants

• mode of action
• uses
• example

Answer 19

• Reduce surface tension of solvents; mechanical removal
• Quats: cationic detergents - antimicrobial
• Detergents: positively charged organic surfactants help other chemicals penetrate fats
• Soaps: hydrophilic and hydrophobic ends lift microbes off skin, generally no antimicrobial

Question 20

Heavy metals

• mode of action
• uses
• example

Answer 20

• Alter the 3-D shape of proteins
• Silver nitrate: surgical dressings, catheters, burn antiseptics
• Copper: controls algae by interfering with chlorophyll

Question 21

Aldehydes

• mode of action
• uses
• example

Answer 21

• Denature propteins and inactivate nucleic acids by cross-linking with amino, hydroxyl, sulfhydryl, and carboxyl functional groups
• Glutaraldehyde: disinfect/sterilize
• Formaldehyde: embalming, disinfection

Question 22

Gaseous agents

• mode of action
• uses
• example

Answer 22

• Denature proteins and DNA by cross-linking functional groups
• Very penetrating. Sterilize mattresses, plastics/rubber goods in hospitals
• Ethylene oxide