Lecture Midterm II Flashcards
Name 4 methods of preserving food
- Refrigeration/freezing
- Desiccation
- Lyophilization
- Osmotic pressure (sugar/salt)
2 advantages and 2 disadvantages of membrane filtration
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
What is the pore size at which the filtrate is considered “sterile?”
0.22 um
Define ionizing radiation
Radiation that carries enough energy to free electrons from atoms or molecules, thereby ionizing them. Wavelength < 1 nm.
What are the effects of ionizing radiation?
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.
Three examples of ionizing radiation
Electron beams
Gamma rays
X-rays
Electron beam characteristics and uses
Effective at killing microbes, but poor penetration.
Uses: sterilize spices, meats, microbiological plastic ware, medical, dental supplies.
Gamma ray characteristics and uses
Penetrate well, but takes hours to kill
Uses: sterilize spices, meats, fresh fruits and vegetables.
X-ray characteristics and uses
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.
Define non-ionizing radiation
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.
Two examples of non-ionizing radiation used in microbial control
UV light
Microwave
UV light characteristics and uses
- Crosslinks DNA (dimers), oxidizes proteins
- Not penetrating, therefore limited usefulness
- Used mostly for sanitizing surfaces, air, or water
Microwave characteristics and uses
- In the presence of water, can kill microbes
- Cannot sterilize dry items, and endospores can be resistant
Name 9 chemical methods of microbial control
- Phenols
- Alcohols
- Halogens
- Oxidizing agents
- Surfactants
- Heavy metals
- Aldehydes
- Gaseous agents
- Antimicrobics
Phenolics
- mode of action
- uses
- example
- Denature proteins and damage plasma membranes. Effective in the presence of organic material.
- Healthcare, laboratories, households.
- Triclosan
Alcohols
- mode of action
- uses
- example
- Dissolve membranes and denature proteins (requires water)
- Antiseptics. Evaporate quickly.
- Ethanol, Isopropanol
Halogens
- mode of action
- uses
- example
- Probably by oxidizing cell components
- Chlorine: bleach, swimming pools, water treatment
- Bromine: hot tubs
- Iodine: betadine
Oxidizing agents
- mode of action
- uses
- example
- Kill by oxidizing proteins/nucleic acids
- Hydrogen peroxide: disinfect/sterilize surfaces
- Ozone: drinking water
- Peracetic acid: sporocide to sterilize equipment
Surfactants
- mode of action
- uses
- example
- 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
Heavy metals
- mode of action
- uses
- example
- Alter the 3-D shape of proteins
- Silver nitrate: surgical dressings, catheters, burn antiseptics
- Copper: controls algae by interfering with chlorophyll
Aldehydes
- mode of action
- uses
- example
- Denature propteins and inactivate nucleic acids by cross-linking with amino, hydroxyl, sulfhydryl, and carboxyl functional groups
- Glutaraldehyde: disinfect/sterilize
- Formaldehyde: embalming, disinfection
Gaseous agents
- mode of action
- uses
- example
- Denature proteins and DNA by cross-linking functional groups
- Very penetrating. Sterilize mattresses, plastics/rubber goods in hospitals
- Ethylene oxide
