Category: Food Processing Unit Operations Objective Questions

250+ TOP MCQs on Mechanical Separation – Centrifugation and Answers

Food Processing Unit Operations Multiple Choice Questions on “Mechanical Separation – Centrifugation”.

1. What is the principle of centrifugation?
a) Sedimentation principle
b) Filtration principle
c) Evaporation principle
d) Size reduction principle

Answer: a
Clarification: Centrifuge works using the sedimentation principle, due to centrifugal acceleration denser substances move outward in the radial direction and that are less dense are displaced and move to the center.

2. What is called centrifugation?
a) Separated through spinning
b) Separate components at higher temperature
c) Separate components at lower temperature
d) Separated through evaporation

Answer: a
Clarification: Centrifugation is the process where a mixture is separated through spinning. It is used to separate skim milk from whole milk, washing machine and blood cells from your blood plasma.

3. Who invented centrifugation?
a) Newton
b) G.G. Stokes
c) Antonin Prandtl
d) Al-Kindi

Answer: b
Clarification: G.G. Stokes invented sedimentation. Newton discovered gravity. Antonin Prandtl invented centrifugation. Al-Kindi invented distillation.

4. What is use of density gradient centrifugation?
a) To purify viruses, ribosomes, membranes
b) Toremovedirt
c) To remove fine particles
d) To remove large particles

Answer: a
Clarification: Density gradient centrifugation is used to purify viruses, ribosomes, membranes. A sucrose density gradient is created by gently overlaying lower concentrations of sucrose on higher concentrations in centrifuge tubes where particles of interest are placed on top in ultracentrifuges. The particles move through the gradient until they reach the same sucrose density and fraction is removed and analyzed.

5. Which of the following statements about differential pelleting centrifugation are correct?
Statement 1: Tissue such as the liver is homogenized by this method.
Statement 2: The overlying solution is placed in another centrifuge tube for progressing steps.
a) True, False
b) True, True
c) False, True
d) False, False

Answer: b
Clarification: Differential pelleting centrifugation is the most common type of centrifugation used. Tissue like liver is homogenized.After sedimentation, the bottom is called pellet and an overlying solution called supernatant. The overlying solution is then placed in another centrifuge tube for progressing steps.

6. What is other name for zonal centrifugation?
a) Isopyniccentrifugation
b) Gradient centrifugation
c) Density gradient centrifugation
d) Differential centrifugation

Answer: b
Clarification: Zonal centrifugation is also known as band or gradient centrifugation and relies on the concept of sedimentation coefficient. In this process, a density gradient is created in a test tube with sucrose and high density at the bottom.

7. Which centrifugation depends on buoyant densities?
a) Isopynic centrifugation
b) Gradient centrifugation
c) Density gradient centrifugation
d) Differential centrifugation

Answer: a
Clarification: Isopynic centrifugation depends on buoyant densities, not on the velocities. CsCl, NaI gradients are the self-forming gradients for macromolecules and nucleotides under centrifugal force.

8. What are applications of centrifugation?
a) To separate two miscible substances and analyze the hydrodynamic properties of macromolecules
b) To separate two miscible substances and water treatment
c) Purification of mammalian cells and water treatment
d) Analyze the hydrodynamic properties of macromolecules and water treatment

Answer: a
Clarification: Applications of centrifugation are separation of two miscible substances, to analyze the hydrodynamic properties of macromolecules, purification of mammalian cells, separating chalk powder from water and removing fat from milk to produce skimmed milk.

9. Is centrifugation used in wine processing?
a) True
b) False

Answer: a
Clarification: Centrifugation is used in wine processing where the wine is clarified and stabilized by using centrifugation process.It is similar to sedimentation principle, where the centrifugal accelerates the denser substances to move outward in the radial direction and that are less dense are displaced and move to the center.

10. Which of the following statements about centrifugation are correct?
Statement 1: Particles are separated from a solution according to their size.
Statement 2: Particles are not separated from a solution according to their shape.
a) True, False
b) True, True
c) False, True
d) False, False

Answer: a
Clarification: Centrifugation is a process of separating substances which involves the centrifugal force. The particles are separated from a solution according to their size, shape, density, the viscosity of the medium and rotor speed.

250+ TOP MCQs on Membrane Separators and Answers

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

1. What is pervaporation?
a) Process to separate a volatile liquid from a non-volatile liquid
b) Process to mix a volatile liquid from a non-volatile liquid
c) Process to a evaporate a non-volatile liquid
d) Process to separate water molecules from a non-volatile liquid
Answer: a
Clarification: Pervaporation is a process to separate a volatile from a non-volatile liquid. The driving force is a vacuum on the gaseous side of the membrane. It is a tool for separation of liquid mixtures.

2. Which method is used for removing hardness?
a) Nanofiltration
b) Pervaporation
c) Electrodialysis
d) Reverse Osmosis
Answer: a
Clarification: Nano filtration is used for removing hardness. It removes organic compounds and selected salts at the lower pressure than RO system. It separates at the molecular level, removing all suspended solids and most dissolved solids.

3. Which method is used separation of azeotrope mixtures?
a) Nano filtration
b) Pervaporation
c) Electro dialysis
d) Reverse Osmosis
Answer: b
Clarification: Pervaporation is a process to separate a volatile from a non-volatile liquid. The driving force is a vacuum on the gaseous side of the membrane. It is a tool for separation of liquid mixtures.

4. Which of the following uses aromatic polyamide as membrane?
a) Gas separation
b) Pervaporation
c) Electro dialysis
d) Reverse Osmosis
Answer: d
Clarification: Reverse Osmosis uses aromatic polyamide as membrane where it is used in separation of salts and micro-solutes from solutions.

5. Which of the following statements about electro dialysis are correct?
Statement 1: Cation and anion exchange membrane is used.
Statement 2: The membrane is made of polymers & co-polymers.
a) True, False
b) True, True
c) False, True
d) False, False
Answer: a
Clarification: Cation and anion exchange membrane is used in electro dialysis where the membrane is made of sulfonated cross-linked polystyrene and is used in desalting the water.

6. What is other name for polymeric membrane?
a) Organic membrane
b) Inorganic membrane
c) Cation and anion membrane
d) Neutral charge membrane
Answer: a
Clarification: Polymeric membranes are also known as organic membranes. In order of the coarsest separation to the finest are microfiltration, ultrafiltration, nanofiltration and reverse osmosis.

7. What is flux rate for filters?
a) Ratio of flow to the membrane area
b) Ratio of concentration to the membrane area
c) Ratio of membrane area to the flow of the solution
d) Ratio of viscosity to the membrane area
Answer: a
Clarification: A membrane’s flux is defined as ratio of flow to the membrane area. It is used for calculating scalability. Ultrafiltration membranes are used in the purification of expensive biomolecules.

8. What is membrane processing?
a) Process that concentrates and separates without the use of heat
b) Process that removes dust without the use of heat
c) Process that remove water without the use of heat
d) Process that remove alcohol without the use of heat
Answer: b
Clarification: Membrane processing concentration and separation without the use of heat. Particles are separated on the basis of size of the molecules and shape with the help of pressure gradient and uses semi-permeable membranes.

9. What are cleaning techniques for the removal of membrane fouling?
a) Air flushing and chemical flushing
b) Alcohol flushing and chemical flushing
c) Air flushing and alcohol flushing
d) Air flushing
Answer: a
Clarification: There are various cleaning techniques to remove membrane fouling. These are forward flushing, backward flushing, air flushing and chemical cleaning.

10. Which of the following is used to remove yeast?
a) Nano filtration
b) Micro filtration
c) Electro dialysis
d) Reverse Osmosis
Answer: b
Clarification: Micro filtration is used for removing yeast, E- coli and mist droplets. Reverse Osmosis and nano filtration is used for removing inorganic compounds.

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,