250+ TOP MCQs on Heat Transfer Applications – Thermal Processing and Answers

Food Processing Unit Operations Multiple Choice Questions on “Heat Transfer Applications – Thermal Processing”.

1. Which describes the level of microbial destruction obtained by thermal treatment?
a) F0 value
b) Thermal death time
c) D value
d) Z value
Answer: a
Clarification: The level of microbial destruct that is obtained by thermal treatment is known as sterilizing value (F0) of the given food product. The results are calculated at 121.1°C temperature. The unit is minutes.

2. ________ relates the resistance of an organism to differing temperatures.
a) F0 value
b) Thermal death time
c) D value
d) Z value
Answer: d
Clarification: Z- value is defined as the temperature (in degree) at which a tenfold reduction in D-value is attained. The main application of Z- value is in the calculating the thermal death time of a microorganism.

3. _________ is defined as the time taken at a given temperature to eliminate at least 90% of the exposed microorganisms.
a) F0 value
b) Thermal death time
c) D value
d) Z value
Answer: c
Clarification: D valueis defined as the time taken at a given temperature to eliminate at least 90% of the exposed microorganisms. It is suitable to examine the efficiency of thermal inactivation of different microbes under different conditions.

4. ________ is the time taken to kill a specific bacterium at a specific temperature.
a) F0 value
b) Thermal death time
c) D value
d) Z value
Answer: b
Clarification: Thermal death time which is also known as TDT is defined as the time taken to destroy a specific microbe at a particular temperature. TDT is used in regulating the sterilization procedures.

5. _______ of a microorganism is the lowest temperature at which all microbes are killed in a 10-minute exposure.
a) F0 value
b) Thermal death time
c) D value
d) Thermal death point
Answer: d
Clarification: Thermal death point is be defined as the lowest temperature at which all the microorganisms are killed in a 10-minute exposure and it varies depending on the microbes. Thermal death point gives the idea of the effect of heat on the microbes.

6. Are these statements about the D value true?
Statement 1: D -value is lower in acid foods.
Statement 2: D-value for the same organism varies depending on the food type.
a) True, False
b) True, True
c) False, True
d) False, False
Answer: b
Clarification: D value is defined as the time taken at a given temperature to eliminate at least 90% of the exposed microorganisms. It is suitable to examine the efficiency of thermal inactivation of different microbes under different conditions. D-value for the same microbes differs depending on the food type. In acid foods, the D value is lower and higher in protein rich foods.

7. __________ is used mainly in low acid canned foods.
a) 12 D concept
b) 1 D concept
c) 10 D concept
d) 100 D concept
Answer: a
Clarification: 12D concept is used generally in low acid canned foods. It refers to thermal processing to reduce the probability of survival of the C. botulinum spores to 10-12 which is high resistant microbe at 121^oC.

8. ______ is the better way of stating thermal death time.
a) F0 value
b) F value
c) D value
d) Z value
Answer: b
Clarification: Thermal death time which is also known as TDT is defined as the time taken to destroy a specific microbe at a particular temperature. F value is defined as the time required killing all spores or vegetative cells at 1210^oC. Therefore F value is the better way of stating thermal death time.

9. _________ is equal to the reciprocal of the slope of the thermal death time curve.
a) F0 value
b) F value
c) D value
d) Z value
Answer: d
Clarification: Z-value is used in the microbial thermal death time calculations. It is defined as the temperature (in degree) at which a tenfold reduction in D-value is attained. It is equal to the reciprocal of the slope of the thermal death time curve.

10. Heat resistance of microorganisms and their spores can be expressed in terms of _______
a) F0 value
b) thermal death time
c) D value
d) thermal death point
Answer: b
Clarification: Heat resistance of microorganisms and their spores can be expressed in terms of thermal death time. Microorganisms are more heat resistant than their spores. Heat resistance of ascospores is 60°C for 10-15 min and the heat resistant of vegetative yeast is 50-58°C in 10-15 min.