29 Questions
What is the relationship between pH and cell energy according to the text?
The lower the pH, the more energy the cell has to spend on maintaining its intracellular pH near neutrality and the less energy it has for other processes.
What is the upper pH limit for growth of most foodborne pathogens?
pH 8 to 9
Which of the following food items has a pH value in the range of 6.5 - 5.3?
Raw beef
What is the purpose of 'hurdle technology' according to the text?
To inhibit microbial growth through the use of antimicrobial agents, ozone, irradiation, and shifts in pH and aw.
What is the typical pH range for foods considered 'low-acid'?
pH >7.0
What is the relationship between pH and processing requirements for food according to the text?
Foods with lower pH values require milder processing than foods with higher pH values.
What was a major cause of deaths during the Middle Ages?
Ergot poisoning
What is the relationship between pH and acidity in food?
A food with a pH of 5 is 100 times more acidic than one with a pH of 7.
What are the two main types of factors that influence microbial growth in food?
Intrinsic and extrinsic factors
Which of the following is an example of an intrinsic factor that influences microbial growth in food?
pH
Which of the following is an example of an extrinsic factor that influences microbial growth in food?
Temperature
What volume of a sample dilution is typically dispensed onto the surface of an agar plate?
1 ml
What is the purpose of using selective or differential media?
To inhibit the growth of all bacteria except the targeted organism
What is the purpose of making a series of dilutions (e.g., 10^-1 to 10^-7) before plating?
To create a range of dilutions that will yield countable colonies
What is the purpose of using a "hockey stick" to spread the sample on the agar surface?
To ensure even distribution of the sample across the entire agar surface
What is a colony-forming unit (CFU)?
A cluster or chain of bacteria that forms a single visible colony
How is the total number of bacteria in a sample calculated?
By multiplying the colony count by the dilution factor
What pH values cause a marked decrease in resistance?
pH values below 5 or above 9
What is the effect of higher temperatures on the heat resistance of C.botulinum spores?
Higher temperatures result in spores with greater heat resistance, possibly through the formation of heat shock proteins.
How do C.botulinum spores of groups I and II compare to most vegetative cells in terms of resistance to irradiation?
C.botulinum spores are more resistant to irradiation compared with most vegetative cells.
Which of the following is not an effective way to inactivate C.botulinum spores?
Irradiation
What is the purpose of the heat treatment given to thermally processed low-acid foods?
To kill spores of C.botulinum but not more heat-resistant spores.
What is the effect of heating on filamentous fungi and yeasts in acidic foods?
Heating for a few minutes at 60-75°C kills most filamentous fungi and yeasts.
What is the primary processing goal for low-acid canned foods?
Inactivate C. botulinum spores
What is the typical time and temperature requirement for achieving a 12D treatment in low-acid canned foods?
3 to 6 minutes at 121°C
What is the definition of the D value?
The time required for a 1-log reduction in viability at a given temperature
What is the definition of the z value?
The temperature change required to alter the D value by a factor of 10
What is the key difference between conventional and aseptic processing of food?
Conventional processing involves hermetically sealing the product in the container, while aseptic processing sterilizes the product outside the container
Which genus of Gram-positive, spore-forming bacteria is known to cause spoilage in juices due to its ability to survive hot-fill processes?
Alicyclobacillus
Explore historical advances towards understanding food poisoning and spoilage from 5000 years ago until AD 1100. Learn about the impact of ergot poisoning caused by a fungus on rye and other grains during the middle ages.
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