This set of Food Microbiology Multiple Choice Questions & Answers (MCQs) focuses on “Thermal Deactivation of Microbes”.
1. The LTLT and HTST methods are used for ___________
a) Pasteurization
b) Drying
c) Chemical deactivation
d) Biological deactivation
View Answer
Explanation: The Low Temperature Long Time (LTLT) and High Temperature Short Time (HTST) methods are used in Pasteurization for the thermal deactivation of microbes. This is a physical method used to preserve food. LTHT uses 336 K for 30 minutes and HTST uses 345 K for 15 seconds.
2. Which of the following is a spore forming bacteria?
a) Coxiella
b) Clostridium
c) Mycobacteria
d) Corynebacteria
View Answer
Explanation: Some bacteria have the ability to produce endospores. Endospores are a highly resistive quiescent form of vegetative bacteria. Non-spore-forming bacteria are usually not pathogenic.
3. The rate of protein denaturation is higher when heated in water rather than air.
a) True
b) False
View Answer
Explanation: Increase in the temperature of the wet proteins produces free–SH groups along with increase in the protein-water binding affinity. Water allows the peptide bonds to cleave. This requires more energy in air.
4. Processing of dairy and dairy products is done by using UHT. What is the full form of UHT?
a) Unit Heat Temperature
b) Unit High Temperature
c) Ultra Handy Temperature
d) Ultra High Temperature
View Answer
Explanation: Ultra Heat Temperatures are usually above 408 K. They are used to sterilize dairy and other dairy products. Due to the very high temperature, sterilization takes a very short time. This process can be called Ultra-Pasteurization.
5. The time required to kill a certain number of organisms at a particular time is called _______
a) TTD
b) TDM
c) TDT
d) TTP
View Answer
Explanation: TDT stands for Thermal Death Time. In this method, the temperature is kept the same and the time required to get rid of all the microbes is calculated.
6. D value gives us the _________ _________ time.
a) Death Toll
b) Decimal Reduction
c) Death Point
d) Decimal Point
View Answer
Explanation: The Decimal Reduction time is the time taken to kill 90% of the microbes in the sample. Mathematically, it is the death rate of an organism. Also, it is numerically equal to the time taken by the survivor curve to get through one log cycle. The time is determined in minutes.
7. The _ value represents the temperature needed for the thermal destruction curve to traverse one log cycle. (Temperature is in Fahrenheit)
a) z
b) a
c) t
d) k
View Answer
Explanation: The z value gives us the temperature needed for the thermal destruction curve to cross one log cycle. Numerically, the reciprocal of the slope of the TDT curve gives us the value of z.
8. Heat resistance is directly proportional to the presence of fats.
a) True
b) False
View Answer
Explanation: Fats can directly affect the amount of moisture. When compared to short-chain fatty acids, long chain fatty acids are much more protective in nature.
9. The _ value gives us the equivalent time (minutes) at 121.1°C of all the heat considered.
a) A
b) E
c) T
d) F
View Answer
Explanation: The F value tells us the equivalent time at the above temperature. It considers all heat w.r.t to its capability to destroy vegetative cells as well as endospores. The F0 value is given by
F0 = Dr(loga – logb)
Where, F0 is the integrated value of all the heat received by the entire container, Dr is the decimal reduction time at the above given temperature, a is the number of cells initially and b is the number of cells in the final population.
10. Which of the following compounds increases heat resistance in microbes?
a) Calcium Chloride
b) Phosphate
c) L-Glutamate
d) L-Proline
View Answer
Explanation: Calcium Chloride decreases water activity thereby increasing the heat resistance. This can be thought of as similar to drying.
Sanfoundry Global Education & Learning Series – Food Microbiology.
To practice all areas of Food Microbiology, here is complete set of Multiple Choice Questions and Answers.
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