Microbiology of Foods Questions and Answers

Q: Food should not be left out of refrigeration for longer than

Correct answer: two hoursTwo hours is the standard cumulative limit for food held between 40 and 140 degrees Fahrenheit. It is chosen so that even a substantial initial contamination cannot multiply to a hazardous level within the time allowed. The limit halves to one hour when the ambient temperature exceeds 90 degrees, since growth is then faster still.

Q: Above what ambient temperature does the two-hour rule shorten to one hour?

Correct answer: 90 degrees FahrenheitAbove 90 degrees Fahrenheit ambient - a hot day, an outdoor buffet, a delivery vehicle in summer - the food warms towards the middle of the Danger Zone quickly and grows faster once there, so the allowance falls from two hours to one. The underlying reasoning is unchanged: the limit is set so that the population cannot reach a hazardous level in the time permitted.

Q: Cold food should be held at or below

Correct answer: 40 degrees FahrenheitForty degrees Fahrenheit, about 4 Celsius, is the upper limit for cold holding and the lower boundary of the Danger Zone. Below it growth of most pathogens is very slow, though not absent - Listeria monocytogenes will grow slowly at refrigeration temperatures, which is why ready-to-eat chilled foods carry use-by dates rather than being treated as indefinitely safe.

Q: Hot food should be held at or above

Correct answer: 140 degrees FahrenheitOne hundred and forty degrees Fahrenheit, about 60 Celsius, is the lower limit for hot holding and the upper boundary of the Danger Zone. Note that this is a holding temperature, not a cooking temperature: cooking must reach considerably higher - 165 degrees for poultry - to reduce the population, whereas holding merely has to prevent regrowth in food already cooked.

Q: Leftovers should be refrigerated within two hours in

Correct answer: shallow containers, for quick coolingA large deep container of hot food cools from the outside inward and its centre may remain in the Danger Zone for hours, which is exactly the condition in which Clostridium perfringens spores germinate and multiply. Dividing the food between shallow containers gives a large surface area and a short conduction path, so the whole mass passes through the Danger Zone quickly. An insulated flask or a covered pot does the opposite.

Q: Refrigeration at 40 degrees Fahrenheit acts by

Correct answer: slowing growth, not killingRefrigeration is bacteriostatic, not bactericidal: it slows metabolism and lengthens the generation time so that the population grows too slowly to matter within the shelf life. The organisms are still present and still viable, and they resume growth as soon as the food warms. This is why chilled food has a limited shelf life and why refrigeration cannot repair food that has already been abused.

Q: The pH value that separates acid foods from low-acid foods is

Correct answer: 4.6A finished equilibrium pH of 4.6 is the regulatory dividing line, chosen because Clostridium botulinum will not grow or produce toxin below it. Foods at or below 4.6 are acid foods and need only a pasteurising heat process; foods above it are low-acid and, if packed hermetically and stored at ambient, require a full botulinum cook. The whole of canning regulation turns on which side of 4.6 a product falls.

Q: An acidified food is defined as a low-acid food to which acid has been added, having a water activity greater than

Correct answer: 0.85An acidified food is a low-acid food to which acid or acid ingredients have been added to bring the finished equilibrium pH to 4.6 or below, and the definition also requires a water activity above 0.85 - below that figure the product is controlled by its dryness instead and falls outside the category. Pickles, acidified vegetables and many sauces are made this way, obtaining ambient stability from pH rather than from a severe heat process.

11.

Food should not be left out of refrigeration for longer than

A.thirty minutes
B.eight hours
C.two hours
D.six hours

Answer: C

Correct answer: two hours

Two hours is the standard cumulative limit for food held between 40 and 140 degrees Fahrenheit. It is chosen so that even a substantial initial contamination cannot multiply to a hazardous level within the time allowed. The limit halves to one hour when the ambient temperature exceeds 90 degrees, since growth is then faster still.

Discuss in Forum

12.

Above what ambient temperature does the two-hour rule shorten to one hour?

A.70 degrees Fahrenheit
B.100 degrees Fahrenheit
C.140 degrees Fahrenheit
D.90 degrees Fahrenheit

Answer: D

Correct answer: 90 degrees Fahrenheit

Above 90 degrees Fahrenheit ambient - a hot day, an outdoor buffet, a delivery vehicle in summer - the food warms towards the middle of the Danger Zone quickly and grows faster once there, so the allowance falls from two hours to one. The underlying reasoning is unchanged: the limit is set so that the population cannot reach a hazardous level in the time permitted.

Discuss in Forum

13.

Cold food should be held at or below

A.40 degrees Fahrenheit
B.50 degrees Fahrenheit
C.32 degrees Fahrenheit
D.60 degrees Fahrenheit

Answer: A

Correct answer: 40 degrees Fahrenheit

Forty degrees Fahrenheit, about 4 Celsius, is the upper limit for cold holding and the lower boundary of the Danger Zone. Below it growth of most pathogens is very slow, though not absent - Listeria monocytogenes will grow slowly at refrigeration temperatures, which is why ready-to-eat chilled foods carry use-by dates rather than being treated as indefinitely safe.

Discuss in Forum

14.

Hot food should be held at or above

A.165 degrees Fahrenheit
B.140 degrees Fahrenheit
C.120 degrees Fahrenheit
D.100 degrees Fahrenheit

Answer: B

Correct answer: 140 degrees Fahrenheit

One hundred and forty degrees Fahrenheit, about 60 Celsius, is the lower limit for hot holding and the upper boundary of the Danger Zone. Note that this is a holding temperature, not a cooking temperature: cooking must reach considerably higher - 165 degrees for poultry - to reduce the population, whereas holding merely has to prevent regrowth in food already cooked.

Discuss in Forum

15.

Leftovers should be refrigerated within two hours in

A.sealed insulated flasks
B.the original cooking pot, covered
C.shallow containers, for quick cooling
D.deep containers, to retain heat

Answer: C

Correct answer: shallow containers, for quick cooling

A large deep container of hot food cools from the outside inward and its centre may remain in the Danger Zone for hours, which is exactly the condition in which Clostridium perfringens spores germinate and multiply. Dividing the food between shallow containers gives a large surface area and a short conduction path, so the whole mass passes through the Danger Zone quickly. An insulated flask or a covered pot does the opposite.

Discuss in Forum

16.

Refrigeration at 40 degrees Fahrenheit acts by

A.killing all bacteria present
B.removing water from the food
C.lowering the pH of the food
D.slowing growth, not killing

Answer: D

Correct answer: slowing growth, not killing

Refrigeration is bacteriostatic, not bactericidal: it slows metabolism and lengthens the generation time so that the population grows too slowly to matter within the shelf life. The organisms are still present and still viable, and they resume growth as soon as the food warms. This is why chilled food has a limited shelf life and why refrigeration cannot repair food that has already been abused.

Discuss in Forum

17.

The pH value that separates acid foods from low-acid foods is

A.4.6
B.7.0
C.5.5
D.3.0

Answer: A

Correct answer: 4.6

A finished equilibrium pH of 4.6 is the regulatory dividing line, chosen because Clostridium botulinum will not grow or produce toxin below it. Foods at or below 4.6 are acid foods and need only a pasteurising heat process; foods above it are low-acid and, if packed hermetically and stored at ambient, require a full botulinum cook. The whole of canning regulation turns on which side of 4.6 a product falls.

Discuss in Forum

18.

The pH threshold of 4.6 matters because below it

A.water activity falls below 0.85
B.C. botulinum spores will not germinate
C.all bacteria are killed immediately
D.yeasts and moulds cannot survive

Answer: B

Acidity below that point prevents germination, which is why such foods can be held at ambient temperature without the severe heat process a low-acid canned food requires. It restrains the organism rather than sterilising the product.

Discuss in Forum

19.

An acidified food is defined as a low-acid food to which acid has been added, having a water activity greater than

A.0.60
B.0.99
C.0.85
D.0.95

Answer: C

Correct answer: 0.85

An acidified food is a low-acid food to which acid or acid ingredients have been added to bring the finished equilibrium pH to 4.6 or below, and the definition also requires a water activity above 0.85 - below that figure the product is controlled by its dryness instead and falls outside the category. Pickles, acidified vegetables and many sauces are made this way, obtaining ambient stability from pH rather than from a severe heat process.

Discuss in Forum

20.

If the equilibrium pH of a finished acidified food is found to be above 4.6, the processor must

A.release it with a shortened shelf life
B.freeze it and release it
C.relabel it as a fermented food
D.reprocess, heat as low-acid, or set aside

Answer: D

Exceeding the threshold removes the safeguard the whole process depends on, so the product cannot simply be released. The options are full reprocessing, treating it as low-acid, or holding it for assessment of public health significance.

Discuss in Forum

Loading…

Topics

Subject Categories

Tags: Microbiology of Foods Questions and Answers || Microbiology of Foods MCQ Questions and Answers || Microbiology of Foods GK Questions and Answers || Microbiology of Foods GK MCQ Questions || Microbiology of Foods Multiple Choice Questions and Answers || Microbiology of Foods GK || GK on Microbiology of Foods || Microbiology Questions and Answers || Microbiology MCQ Questions and Answers || Microbiology GK Questions and Answers || GK on Microbiology

Microbiology of Foods Questions and Answers

Topics

Subject Categories

About Us

Stay informed about all important Dates & Notifications