This set of Food Processing Unit Operations Multiple Choice Questions & Answers (MCQs) focuses on “Freeze Drying”.
1. What is alternative name for freeze drying?
a) Lyophilisation
b) Cold pasteurization
c) Irradiation
d) Liposuction
View Answer
Explanation: The freeze drying is also known as lyophilisation where a low temperature dehydration process takes place. This involves 1.Freezing the product 2. Lowering the pressure and then removing the ice by the sublimation process.
2. What is cryodesiccation?
a) Freeze drying
b) Cold pasteurization
c) Irradiation
d) Dehydration
View Answer
Explanation: The freeze drying is also known as cryodesiccation. In this process, dehydration takes place at a very low temperature. This is divergence to the dehydration by all the conservative methods that vaporize water using the heat.
3. During the primary drying phase in freeze drying, What is necessary to calculate amount of heat required?
a) By using latent heat of sublimation
b) By using latent heat of vapourization
c) By using enthaply
d) By using specific heat
View Answer
Explanation: During the primary drying phase in freeze drying, the pressure is lowered and heat is given to the product for the ice sublimation. The amount of heat necessary is calculated using the latent heat of sublimation of the sublimating molecules.
4. Which of the following governs the process in secondary drying in freeze drying?
a) Latent heat of sublimation
b) Latent heat of vapourization
c) Enthaply
d) Adsorption isotherms
View Answer
Explanation: The secondary drying phase of the freeze-drying process is overseen by the adsorption isotherms of the material. In this phase, the temperature is raised greater than in the primary drying phaseto disrupt any physicochemical interfaces that have formed between the frozen material and water molecules.
5. At what point the ice crystal formation takes place?
a) When the material is cooled below itstriple point
b) When the material is cooled below its freezing point
c) When the material is cooled below its dew point
d) When the material is cooled above its triple point
View Answer
Explanation: During the freezing stage, the product is cooled below its triple point, this is achieved to ensure that melting does not takes place. Triple point is the lowest temperature at which the liquid, solid and gas stages of the material can coexist.
6. What is the main advantage of annealing?
a) It is done to achieve largeice crystals
b) It is done to achieve smallice crystals
c) It is done to achieve microscopicice crystals
d) It is done to achieve mixture of large and small ice crystals all
View Answer
Explanation: The large ice crystals promote faster removal of water vapor due to formation of a network within the product during sublimation. Therefore annealing is done to achieve larger crystals where the product is slowly frozen.
7. Which of the following is known to result in the highest quality of foods amongst all drying techniques?
a) Freeze drying
b) Cold pasteurization
c) Osmotic dehyradtion
d) Evaporation
View Answer
Explanation: Freeze drying produces highest quality of foods amongst all other drying techniques. This is mainly due to structural integrity and preservation of flavors of the product during the freezing process.
8. How long does freeze drying take?
a) 10 to 40 hours
b) 20 to 40 hours
c) 30 to 50 hours
d) 5 to 20 hours
View Answer
Explanation: It takes between 20 to 40 hours to complete the process. Food type, quantity, thickness affects the freeze-dry cycle. Products like peas, meat, corn dry quickly whereas squash can take longer.
9. What foods cannot be freeze dried?
a) Foods with high fiber content
b) Foods with high Vitamin B12 content
c) Foods with high protein content
d) Foods with high fat content
View Answer
Explanation: Most of the foods are suitable for freeze drying like fruits, vegetables, dairy products, meat, dry liquids like soup or yogurt and instant coffee. Foods with high fat are not suitable for freeze drying as the fat melts damages the equipment.
10. Who discovered freeze drying?
a) Jacques-Arsened’Arsonval
b) Charles Chamberland
c) Willis Carrier
d) Clarence Birdseye
View Answer
Explanation: Jacques-Arsened’Arsonval discovered freeze drying. Charles Chamberl and developed the first pressure steam sterilizer. Willis Carrier invented the chillers. Clarence Birdseye developed processes for freezing fish based on quick freezing.
Sanfoundry Global Education & Learning Series – Food Processing Unit Operations.
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