Category: Food Processing Unit Operations Objective Questions

250+ TOP MCQs on Freeze Drying and Answers

Food Processing Unit Operations Multiple Choice Questions on “Freeze Drying”.

1. What is alternative name for freeze drying?
a) Lyophilisation
b) Cold pasteurization
c) Irradiation
d) Liposuction
Answer: a
Clarification: 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
Answer: a
Clarification: 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
Answer: a
Clarification: 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
Answer: d
Clarification: 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
Answer: a
Clarification: 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
Answer: a
Clarification: 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
Answer: a
Clarification: 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
Answer: c
Clarification: 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
Answer: d
Clarification: 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
Answer: a
Clarification: 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.

250+ TOP MCQs on Heat Convection and Answers

Food Processing Unit Operations Multiple Choice Questions on “Heat Convection”.

1. Which of the following example explain convection?
a) The heat from a hot liquid makes the cup itself hot
b) Walking on the beach on a hot summer day will warm the feet
c) A metal spoon becomes hot from the boiling water inside the pot
d) The formation of sea and land breeze
Answer: d
Clarification: The formation of sea and land breeze is an example of convection. During a day, the sun the sun warms the ground and sea water. Since the ground has lower specific heat compared to water and so its temperature increases more than the temperature of the water. The air above ground is heated thus forming a rise in the convection currents and the cool air from over sea flows towards shore. This is called as sea breeze. Similarly in the evening, ground cools faster than water and therefore breeze flows from shore to sea.

2. Which law governs the thermal convection?
a) Fourier’s law
b) Pascal law
c) Newton’s law
d) Stefan-Boltzmann Law
Answer: c
Clarification: Newton’s law governs the thermal convection especially in convection cooling. It states that rate of heat loss of a body is directly proportional to the temperature difference between the body and its surroundings.

3. ___________ is the transfer of thermal energy through the movement of a liquid or gas.
a) Convection
b) Conduction
c) Radiation
d) Evaporation
Answer: a
Clarification: Convection is the transfer of thermal energy through the movement of a liquid or gas.Convection can be defined as the heat transfer by the movement of a fluid between areas of temperature difference.

4. Is conduction faster than convection?
a) True
b) False
Answer: b
Clarification: Convection is faster than conduction. In convection the medium in which heat transfer takes place is in motion whereas the heat transfer through conduction takes place by collision between the atoms.

5. Are these statements about the thermal convection true?
Statement 1: Thermal convection depends on temperature gradient.
Statement 2: It does not depend on relative motion of the fluid.
a) True, False
b) True, True
c) False, True
d) False, False
Answer: a
Clarification: The properties of heat transfer by the convection between a body and its surrounding are 1. The convection takes place when there is temperature difference between two medium. 2. It depends on the relative motion of the fluid as convection takes place only when the medium has movement.

6. _________ is the currents produced only by temperature difference.
a) Natural convection
b) Forced convection
c) Conduction
d) Radiation
Answer: a
Clarification: Natural convection is a type of convection where the heat transfer takes place only due to density difference that leads to the temperature difference in the fluid. The gravitational force is the main driving force in the natural convection.

7. In __________, fluid is forced to flow over a surface or in a tube by external means.
a) natural convection
b) forced convection
c) conduction
d) radiation
Answer: b
Clarification: Forced convection is a mechanism of heat transfer in which fluid motion is produced by an external source such as ceiling fan, a pump and suction device. It creates uniform and comfortable temperature throughout the medium.

8. Convective heat transfer coefficients for air under natural convection is __________
a) 0.5 – 1000 (W/(m2K))
b) 50 – 3000 (W/(m2K))
c) 10 – 1000 (W/(m2K))
d) 50 – 10000 (W/(m2K))
Answer: a
Clarification: Convective heat transfer coefficients for air under natural convection is 0.5 – 1000 (W/(m2K)). For liquids under natural convection is 50 – 3000 (W/(m2K)). For air under forced convection it is 10 – 1000 (W/(m2K)). For liquids under forced convection it is 50 – 10000 (W/(m2K)).

9. Convective heat transfer coefficients for condensing water vapor is __________
a) 0.5 – 1000 (W/(m2K))
b) 5 – 100 (W/(m2K))
c) 10 – 1000 (W/(m2K))
d) 50 – 10000 (W/(m2K))
Answer: b
Clarification:A convective heat transfer coefficient for condensing water vapor is 5 – 100 (W/ (m2K)). It is proportionality constant between heat flux and temperature difference that plays an important factor as driving force for the flow of heat.

10. Convective heat transfer coefficients for liquid under forced convection is __________
a) 0.5 – 1000 (W/(m2K))
b) 50 – 3000 (W/(m2K))
c) 10 – 1000 (W/(m2K))
d) 50 – 10000 (W/(m2K))
Answer: d
Clarification: Clarification: Convective heat transfer coefficients for air under natural convection is 0.5 – 1000 (W/(m2K)). For liquids under natural convection is 50 – 3000 (W/(m2K)). For air under forced convection it is 10 – 1000 (W/(m2K)). For liquids under forced convection it is 50 – 10000 (W/(m2K)).

250+ TOP MCQs on Process Engineering Applications – Dairy Industry and Answers

Food Processing Unit Operations Multiple Choice Questions on “Process Engineering Applications – Dairy Industry”.

1. What is other name for batch pasteurization?
a) Vat Pasteurization
b) HTST pasteurization
c) UHT pasteurization
d) Cold pasteurization
Answer: a
Clarification: Vat Pasteurization is also known as the holding method or batch pasteurization. Every particle of milk or cream is heated in equipment at 63°C and hold for 30 minutes.

2. What happens when milk is pasteurized?
a) Reduces the bacterial population
b) Destroys spores
c) Impart color
d) Impart flavor
Answer: a
Clarification: Pasteurization is not similar to sterilization. Pasteurization reduces the bacterial population of a liquid and destroys the organisms that may cause spoilage and human disease. Spores are not affected by the pasteurization process.

3. What happens when milk is sterilized?
a) Reduces the bacterial population
b) Destroys spores
c) Impart color
d) Impart flavor
Answer: b
Clarification: Pasteurization is not similar to sterilization. Spores are not affected by the pasteurization process. But the sterilization process destroys the spores of the bacteria by inactivating them.

4. What is the chilling temperature of milk?
a) 1-2°C
b) 3-4°C
c) 5-6°C
d) 6-7°C
Answer: b
Clarification: The chilling of milk is done by quick cooling of the raw milk to adequately low temperature. So that the growth of microbes present in milk is inactivated. In chilling process, the temperature of milk should be around 3 – 4°C.

5. What is the temperature of ultra-pasteurization for milk?
a) 125 – 138°C
b) 115 – 120°C
c) 63°C
d) 63 – 65°C
Answer: c
Clarification: Ultra-pasteurization temperature is 125 – 138°C for 2-4 seconds. Sterilization of milk in container is 115 – 120°C for 20-30 minutes. LTLT pasteurization of milk is 63°C for 30 minutes and for thermisation it is 63 – 65°C for 15 seconds.

6. What is bactofugation?
a) Process of removal of microorganisms from milk using centrifugal force
b) Process of removal of yeast and fungi from milk using centrifugal force
c) Process of removal of microorganisms from milk using gravitational force
d) Process of removal of yeast and mold from milk using gravitational force
Answer: a
Clarification: Bactofugation is the process of removal of microorganisms from milk using centrifugal force. It is a special form of separation of microbes, mainly spore formers.

7. Which of the following dryer used to manufacture milk powder?
a) Spray dryer
b) Cabinet tray dryer
c) Pneumatic dryer
d) Fluidized bed dryer
Answer: a
Clarification: Spray dyer is used to produce powder from the solution. It dries the solution stream and separates the solute and evaporates the solvent and forms vapor. The solid particles are collected in a cyclone or drum.

8. What is the temperature of LTLT pasteurization for milk?
a) 125 – 138°C
b) 115 – 120°C
c) 63°C
d) 63 – 65°C
Answer: c
Clarification: Ultra-pasteurization temperature is 125 – 138°C for 2-4 seconds. Sterilization of milk in container is 115 – 120°C for 20-30 minutes. LTLT pasteurization of milk is 63°C for 30 minutes and for thermisation it is 63 – 65°C for 15 seconds.

9. What is skimming efficiency?
a) The amount of fat that can be separated from milk
b) The amount of skim milk that can be separated from whole milk
c) The amount of fat that is added to milk
d) The amount of skim milk that is added to whole milk
Answer: a
Clarification: The amount of fat that can be separated from milk and it depends on the design of the separator, the flow rate of milk and the size distribution of the fat globules.

10. What is the temperature of thermisation for milk?
a) 125 – 138°C
b) 115 – 120°C
c) 63°C
d) 63 – 65°C
Answer: d
Clarification: Ultra-pasteurization temperature is 125 – 138°C for 2-4 seconds. Sterilization of milk in container is 115 – 120°C for 20-30 minutes. LTLT pasteurization of milk is 63°C for 30 minutes and for thermisation it is 63 – 65°C for 15 seconds.

250+ TOP MCQs on Mechanical Separation – Sedimentation Equipment and Answers

Food Processing Unit Operations Questions and Answers for Entrance exams on “Mechanical Separation – Sedimentation Equipment”.

1. What should be the velocity for the sedimentation process?
a) High
b) Low
c) Does not depend
d) Very high
Answer: b
Clarification: In sedimentation tank, the continuous flow through the equipment is commonly desired, so therefore the flow velocities have to be low enough to avoid unsettling of the sediment.

2. What is flotation?
a) Removal of fine particles by air bubbles
b) Removal of fine particles by sedimentation
c) Removal of fine particles by chelating agents
d) Removal of large particles by air bubbles
Answer: a
Clarification: In some cases, where it is difficult to remove fine particles, therefore floatation equipment is used where these are floated to the surface with the help of air bubbles.

3. Which of the following food industry uses floatation equipment?
a) Sugar industry
b) Oil industry
c) Bakery industry
d) Salt industry
Answer: b
Clarification: In the food industry, floatation is used in the separation of small particles of fat from water. The air dissolved in water under pressure produces the froth. When the pressure suddenly released, the air comes out of solution in the form of bubbles which rise and carry the fat with them to surface.

4. What is limitation of large sedimentation tank?
a) Regarding contact time
b) Regarding efficiency
c) Regarding quality
d) Regarding quantity
Answer: a
Clarification: The disadvantages of large sedimentation tank are the slow rate of sedimentation, it requires large chamber areas and the long contact times between particles and the heated air that results in deterioration of heat-sensitive products.

5. What is the accumulated at the bottom in sedimentation tank?
a) Solute
b) Solvent
c) Solution
d) Sludge
Answer: d
Clarification: In the sedimentation tank, a layer of accumulated solids is formed at the bottom of the tank and is periodically removed. This is known as sludge.

6. Is ballasted flocculation a physical-chemical sedimentation process?
a) True
b) False
Answer: a
Clarification: Ballasted flocculation is a high-rate, physical-chemical sedimentation process involving the fixing of flocs, or suspended solids, onto ballast generally sand with the help of a polymer.

7. What are clarifiers?
a) Horizontal basin sedimentation tank
b) Circular basin sedimentation tank
c) Vertical basin sedimentation tank
d) Square basin sedimentation tank
Answer: b
Clarification: The Circular basins are called as clarifiers. These basins are similar to rectangular basins, but are more prone to short circuiting and particle removal problems.

8. How is sludge removed from sedimentation tank?
a) Scraper
b) Air
c) Vacuum devices
d) Scraper and vacuum devices
Answer: d
Clarification: The Sludge is removed from the sludge zone in sedimentation tank by scraper or vacuum devices which move along the bottom. Low flow velocities are allowed to enter the sludge zone, or else the sludge could be swept up and out of tank.

9. What is the largest portion of the sedimentation basin?
a) Sludge zone
b) Settling zone
c) Inlet zone
d) Outlet zone
Answer: b
Clarification: The settling zone is the largest portion of the sedimentation basin. This zone provides the area essential for the settling of the suspended particles.

10. Are these statements about the rectangle sedimentation tank true?
Statement 1: Low tolerance to shock overload.
Statement 2: Minimal short circuiting.
a) True, False
b) True, True
c) False, True
d) False, False
Answer: c
Clarification: Rectangular sedimentation basins are used in large-scale water treatment plants. They are high tolerance to shock overload. It is cost effectiveness due to lower construction cost and lower maintenance. It has minimal short circuiting.

Food Processing Unit Operations for Entrance exams,

250+ TOP MCQs on Membrane Separation and Answers

Food Processing Unit Operations Multiple Choice Questions on “ Membrane Separation”.

1. What are the classifications of membrane separation?
a) Pore size
b) Separation driving force
c) Separation driving pressure
d) Separation driving force and pore size
Answer: d
Clarification: Membrane separations are classified by pore size and by the separation driving force. It is a technology which selectively separates materials via pores and minute gaps in the molecular arrangement of a continuous structure.

2. What is pore size of RO membranes?
a) 0.0005 microns
b) 0.005 microns
c) 0.05 microns
d) 0.5 microns
Answer: a
Clarification: The pore size of RO membrane is 0.0005 microns, this is smaller than the size of the sodium chloride molecule which has the size of 0.0007 micron and will not let it through membrane.

3. What are the applications of membrane separation?
a) Nano filtration
b) Microfiltration
c) Ultrafiltration
d) Microfiltration, ultrafiltration, nano-filtration
Answer: d
Clarification: The membrane processes are used in microfiltration, gas separation, ultrafiltration, membrane distillation, nanofiltration, reverse osmosis, electrolysis, dialysis, electro dialysis and membrane contactors.

4. What is filter membrane made up of?
a) Thin layer of collodion, cellulose acetate
b) Thick layer of collodion, cellulose acetate
c) Thin layer of collodion
d) Thin layer of cellulose acetate
Answer: a
Clarification: The membrane filter is a filter which is made up of a thin film of collodion, cellulose acetate, available in a wide range of defined pore sizes.

5. What is permeate?
a) Fluid that has retained in semi-permeable membrane
b) Fluid that has passed through semi-permeable membrane
c) Fluid that has to be passing through semi-permeable membrane
d) The residue after filtration
Answer: b
Clarification: The membrane separation system splits stream into two fold effluent streams. They are permeate and concentrate. Permeate is defined as the fluid that passes through the semi-permeable membrane.

6. Are these statements about the membrane separation process true?
Statement 1: It replaces the conventional processes like filtration, distillation, ion-exchange and chemical treatment systems.
Statement 2: Greater flexibility in designing systems.
a) True, False
b) True, True
c) False, True
d) False, False
Answer: b
Clarification: Advantages of membrane separation process are appreciable energy saving, clean technology with operational ease and it replaces the conventional processes like filtration, ion-exchange and chemical treatment systems and finally greater flexibility in designing systems.

7. What are classification of membranes from a structural point of view ?
a) Asymmetrical and pore size
b) Symmetrical and pore size
c) Symmetrical and asymmetrical
d) Symmetrical and concentration of solute
Answer: c
Clarification: From a structural point of view membranes are broadly divided into two types. They are Symmetrical and asymmetrical which is also called as anisotropic.

8. What are the driving forces in membrane separation?
a) Osmotic pressure
b) Electrical field
c) Partial pressure
d) Osmotic pressure, electrical field and partial pressure
Answer: d
Clarification: The driving forces in membrane separation are transmembrane (hydrostatic) pressure (TMP), concentration or electrochemical gradient, osmotic pressure electrical field and partial pressure.

9. Is micro filtration is used to remove biological entities in the 0.25 μm to 5.0μm range?
a) True
b) False
Answer: a
Clarification: The micro filtration is used to remove biological entities in the 0.025 μm to 10.0μm range from fluids by passage through a microporous medium like a membrane filter.

10. Which of the following are in the order of descending order?
a) Nano filtration, ultrafiltration, Reverse osmosis and microfiltration
b) Reverse osmosis, nano filtration, ultrafiltration and microfiltration
c) Microfiltration, ultrafiltration, nano filtration and reverse osmosis
d) Ultrafiltration, microfiltration, nano filtration and reverse osmosis
Answer: c
Clarification: Membrane processes are classified into four types based on size of component in the feed solution. The descending orders are microfiltration, ultrafiltration, nano filtration and reverse osmosis.

250+ TOP MCQs on Sun Drying and Answers

Food Processing Unit Operations Multiple Choice Questions on “Sun Drying”.

1. Why meats are not recommended for out-of-doors drying?
a) Meats are high in protein, making them ideal for microbial growth
b) Meat gets decomposed easily
c) Meat absorbs the outdoor odours
d) Vitamin B12 is lost during sun drying
Answer: a
Clarification: Meats are high in protein, making them ideal for microbial growth. Along with the microbial spoilage it can also undergo oxidation and enzymatic autolysis which further decreases the quality of the meat.

2. What is hybrid solar dryer?
a) It is designed and constructed using direct solar energy and a heat exchanger.
b) It represents solar dyer but uses irradiation instead of sun rays
c) It is designed and constructed using direct solar energy and irradiation rays
d) It is used for only hybrid and genetically modified foods
Answer: a
Clarification: A hybrid solar dryer was designed and constructed using direct solar energy and a heat exchanger. The dryer was operated during normal sunny days as a solar dryer. Drying is carried out at night with stored heat energy in water which was collected during the sun-shine time and with electric heaters.

3. What is the lower limit of moisture content by sun drying method?
a) 15%
b) 10%
c) 8%
d) 13%
Answer: a
Clarification: The lower limit of moisture content by sun drying method is approximately 15%. For sun drying of foods, hot days are required with minimum temperatures of 35°C and also with the low humidity.

4. Is sun drying and solar drying same?
a) True
b) False
Answer: b
Clarification: In sun drying, the product is exposed directly to solar radiation and more or less effectively to the wind. In solar drying, the produce is contained in an enclosed space, and the air in contact with it is heated by solar radiation.

5. Are these statements about the location for the sun drying true?
Statement 1:Low lying swampy areas are preferred for the sun drying of the products.
Statement 2:High relative humidity is preferred.
a) True, False
b) True, True
c) False, True
d) False, False
Answer: d
Clarification: The location for the sun drying is selected to take the maximum advantage of climatic conditions. Low lying swampy areas with a high relative humidity should be avoided and racks should be sited away from forests or high buildings which will reduce the air movement or cast a shadow over the racks.

6. What are the modes of heat transfer employed in solar drying systems?
a) Radiation and convection
b) Conduction and convection
c) Conduction and radiation
d) Radiation and conduction
Answer: a
Clarification: Solar drying systems can be categorized mostly on the basis of the mode of transfer of heat engaged. These are radiation and forced convection. Drying is a twofold process which includes 1.The heat transfer to the product from a heating source and 2.Mass transfer of moisture from the interior of the product to its surface and from the surface to the surrounding air.

7. Are these statements about the solar dryer true?
Statement 1: It is designed to collect and enhance solar radiation.
Statement 2: This drier is faster than sun-drying
a) True, False
b) True, True
c) False, True
d) False, False
Answer: b
Clarification: Solar dryer is designed to collect and enhance solar radiation. This drier is faster than sun drying and also requires less drying area but cannot be used on cloudy days.

8. What type of air temperature and humidity do the solar driers generate?
a) Highair temperature, lowhumidity
b) Lowair temperature, high humidity
c) Lowair temperature, lowhumidity
d) Highair temperature, highhumidity
Answer: a
Clarification: Solar driers generate low humidity and high air temperature which results in faster drying. Solar driers are more expensive that natural sun drying but is faster compared to the sun drying.

9. What are advantages of sun drying?
a) Economical and environmentally friendly
b) Fast drying and environmentally friendly
c) Environmentally friendly
d) Economical
Answer: a
Clarification: Sun drying is the most common, cost-effective and environmentally friendly method of preservation of agricultural products. The demerits of this process are that exposure of produce to weather elements such as rain, UV rays of the sun, contamination by wind-borne dirt and infestation by pests and other microbes.

10. Which of the following is an important parameter in sun drying rate?
a) Convective heat transfer coefficient
b) Conductive heat transfer coefficient
c) Mass transfer coefficient
d) Dynamic mass transfer coefficient
Answer: a
Clarification: A portion of the sun radiation incident on the uneven surface of the groundnut reflects back into the environment. The remaining part of the sun energy is absorbed by the product surface and hence increases the product surface temperature which propagates the water vapor formation inside the product. Then the diffusion of water vapor gets started and the mass of the product decreases from the surface of the product.