Engineering Questions with Answers - Multiple Choice Questions
Primary Production of Milk Engineering MCQs
After centrifugation when sublimate settles, clear liquid _____________
a) can be allowed to rest
b) can be allowed to form crystals
c) can be decanted off
d) can be evaporated
Explanation: Centrifugation separates sublimate and whey. Once the sublimate settles after centrifugation, clear liquid can be decanted off.
After centrifugation, sublimate ______
a) dissolves completely
b) remain suspended in a liquid
c) settles at bottom
d) depends upon pH of sublimate
Explanation: These particles can sediment at the bottom of the tube into what’s known as a pellet, and this isolated specimen, or the remaining solution, the supernatant, can be further processed or analyzed.
Which of the following is an effective way of purifying liquids containing suspensions?
d) separating funnel
Explanation: A suspension is a heterogeneous mixture containing solid particles that are sufficiently large for sedimentation. Liquids containing suspension can be purified using centrifugation.
Fine insoluble solid particles can be removed through which of the following process?
d) separating funnel
Explanation: Decantation is a process for the separation of mixtures, by removing a layer of liquid, generally one from which a precipitate has settled. Centrifugation helps in the removal of fine insoluble particles in a solution.
Process quicker than filtration but not so effective is __________
d) fractional distillation
Explanation: Decanting is a process to separate mixtures. Decanting is just allowing a mixture of solid and liquid or two immiscible liquids to settle and separate by gravity. This process can be slow and tedious without the aid of a centrifuge.
Differential centrifugation relies on the differences in ______ of biological particles of different ___________
a) Size, density
b) Sedimentation rate, sizes and density
c) Size, structure
d) Mass, size
Explanation: Differential centrifugation is a process which is used to separate certain organelles from whole cells for further analysis of specific parts of cells. Differential centrifugation is a process based on the differences in the sedimentation rate of biological particles of different sizes and density.
Which of the following statements about the basic principle of sedimentation is False?
a) The denser a biological structure is, the faster it sediments in a centrifugal field
b) The more massive a biological particle is, the slower it moves in a centrifugal field
c) The denser the buffer system is, the slower the particle will move in a centrifugal field
d) The greater the centrifugal force is, the faster the particle sediments
Explanation: Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier. The statement is false because the more massive a biological particle is, the faster it moves in a centrifugal field.
Which of the following is/are the application of analytical centrifugation? I. The determination of the purity of macromolecules. II. The determination of the relative molecular masses of solutes in their native state. III. The examination of changes in the molecular mass of supramolecular complexes. IV. The detection of conformational changes.
a) I only
b) I and II only
c) I, II and III only
d) I, II, III and IV
Explanation: Analytical ultracentrifugation (AUC) is a versatile and powerful method for the quantitative analysis of macromolecules in solution. All of these are application of analytical centrifugation.
Which of the following is/are appropriate care and maintenance of centrifuges? I. Proper balancing of centrifuge tubes. II. Avoid long time exposure of the rotors to alkaline solution and acidic buffers. III. Cleaning centrifuges and rotors with coarse brushes and then wash them with distilled or de-ionized water after every run. IV. For overnight storage, the rotors are left upside down and then positioned in a safe and dry place.
a) I, II, III only
b) II, III and IV only
c) I, II, and IV only
d) II only
Explanation: Only option I, II and IV are appropriate care and maintenance of centrifuges. However, cleaning centrifuges and rotors with coarse brushes may cause damage to the protective layers of rotors. Therefore, option iii is wrong.
After centrifugation of milk, the supernatant is?
Explanation: After centrifugation of milk, the whey is left as the supernatant. A separator is a centrifugal device which aids in separation of milk into cream and skimmed milk.
What is the name of the machine that spins in order to separate out components making up a mixture?
b) Blood plasma
d) Centrifugation tube
Explanation: A centrifuge is a machine with a rapidly rotating container that applies centrifugal force to its contents, typically to separate fluids of different densities (e.g. cream from milk) or liquids from solids.
How does centrifugation work?
a) Through dripping particles
b) Through spinning
c) By keeping large particle in the center and smaller on the outside
d) By separating particles into different tubes
Explanation: The centrifuge works using the sedimentation principle, where the centripetal acceleration causes denser substances and particles to move outward in the radial direction. At the same time, objects that are less dense are displaced and move to the center.
If you were centrifuging whole milk, which would you expect to get flung further out from the center of the centrifuge?
a) The cream/fat
b) Both would be equally flung
c) The skim milk
d) Neither would be flung
Explanation: When spun, the heavier milk is pulled outward against the walls of the separator and the cream, which is lighter, collects in the middle. The cream and milk then flow out of separate spouts.
Which of the following scientist invented the centrifugal separator?
a) Gustaf de Laval
b) Donald ronholm
c) Luis pastuer
Explanation: From 1890 the separators built by Gustaf de Laval were equipped with specially designed conical discs, the patent on which had been granted in 1888.
The skimming efficiency of a separator consequently decreases with increased throughput.
Explanation: The flow velocity through the separation channels will be reduced if the flow rate through the machine is reduced. Thus providing the fat globules more time to rise and be discharged through the cream outlet. The skimming efficiency of a separator consequently increases with a decrease in throughput and vice versa.
Standardization of milk involved which of the following?
a) Adjustment of fat content
b) Breakdown of protein
c) Whitish appearance of milk
d) Increase in nutritional content of milk
Explanation: Standardization of fat content involves adjustment of the fat content of milk, or a milk product, by addition of cream or skim milk as appropriate to obtain a given fat content.
Which of the following method is used in a standardization of milk?
a) Pearson square method
b) Donald method
c) Jake method
d) Pearson cube method
Explanation: One of these methods, frequently used, is taken from the Dictionary of Dairying by J.G. Davis and is illustrated by Pearson square method. How many kgs of cream of A% fat must be mixed with skim milk of B% fat to make a mixture containing C% fat? The answer is obtained from a square, where the given figures for fat contents are placed.
he pressure in the skim milk outlet must be kept _______ in order to enable accurate standardization.
Explanation: The pressure in the skim milk outlet must be kept constant in order to enable accurate standardization. This pressure must be maintained regardless of variations in flow or pressure drop caused by the equipment after separation, and this is done with a constant-pressure valve located close to the skim milk outlet.
Which of the factor does not affect the precision in standardization process?
a) Fluctuations in the fat content of the incoming milk
b) Fluctuations in throughput
c) Fluctuations in preheating temperature
d) Fluctuation in protein content
Explanation: For precision in the process it is necessary to measure variable parameters such as fluctuations in the fat content of the incoming milk, fluctuations in throughput, and fluctuations in preheating temperature. Most of the variables are interdependent; any deviation in one stage of the process often results in deviations in all stages.
The cream fat content is _______ to the flow rate.
a) Inversely proportional
b) Directly proportional
c) Neither inversely proportional nor directly proportional
Explanation: The cream fat content is inversely proportional to the flow rate. Some standardization systems therefore use flow meters to control the fat content.
What is the objective of Bactofugation?
a) Separate microorganisms from milk
b) Separate fat from skim milk
c) Standardize milk
d) Separate fat globules
Explanation: Bactofugation is a Belgian process for removing bacteria from milk by high speed centrifugation. It aims at separation of microorganisms from milk.
Which of the following device is used in Bactofugation?
Explanation: Bacteria, especially heat resistant spores, have a significantly higher density than the milk. A Bactofuge is therefore a particularly efficient means of ridding milk of bacteria spores. Since these spores are also resistant to heat treatment, the Bactofuge makes a useful complement to thermisation, pasteurization and sterilization.
Major Application of Bactofugation is in which of the following processing?
a) Wine processing
b) Juice processing
c) Cheese processing
d) Ice cream processing
Explanation: Bacteria belonging to the genus Clostridium – anaerobic spore-forming bacteria – are among the most feared by cheese makers, as they can cause late blowing of cheese even if present in small numbers. That is why cheese milk is bactofugated.
The amount of bactofugate from the two-phase Bactofuge ______ as compared to one-phase Bactofuge.
Explanation: The amount of bactofugate from the two-phase Bactofuge is about 3% of the feed, while the corresponding amount from the one-phase Bactofuge can be as low as 0.15% of the feed.
A decanter centrifuge is a machine for continuous sedimentation of suspended solids from a liquid by the action of ________in an elongated, horizontal rotating bowl.
a) Centrifugal force
b) Gravitation force
c) Friction force
d) Force of resistance
Explanation: A decanter centrifuge separates solid materials from liquids in the slurry by centrifugal force. It plays an important role in wastewater treatment, chemical, oil and food processing industries.
How much whole milk with 3.9% fat and skimmed milk with 0.04% fat content will you need to produce 2000 kg of standardized milk with 2.5% fat?
a) 725.4 kg
b) 825.4 kg
c) 925.4 kg
d) 715.4 g
Explanation: Using Pearson’s Square method:
Proportion of the whole milk = 2.46/3.86
Amount of whole milk required = (2.46/3.86)*2000 = 1274.6 kg
Proportion of skimmed milk = 1.4/3.86
Amount of skimmed milk required = (1.4/3.86)*2000 = 725.4 kg (or 2000 – 1274.6).
500 kg of milk testing 6.5% fat to be standardized to 3.1% fat using skim milk containing 0.05% fat. Therefore, the quantity of skim milk required to be added to 500 kg whole milk will be?
a) 557.38 kg
b) 440 kg
c) 850 kg
d) 500 kg
Thus mixing of 3.05 kg of 6.5% fat milk with 3.40 kg of the skim milk will yield 6.45 kg of milk containing the desired fat level i.e. 3.1%. Therefore, the quantity of skim milk required to be added to 500 kg whole milk will be (3.4 x 500)/3.05=3.05. Accordingly, 557.38 kg of 0.05% skim milk mixed with 500 kg of 6.5% fat whole milk will yield 1057.38 kg of milk having 3.1% fat.
Which of the following standardization is more desirable in large-scale operation?
c) No standardization
Explanation: Continuous, on-line blending is much more desirable in a large-scale operation. This can be achieved on the cream separator itself by allowing sufficient cream to remix with the skim milk so that the mixture is milk with the desired fat content; the balance cream flows through the cream line into the cream tank. This requires that the separator is fitted with a standardizing device.
How many parts by weight of 40% cream and 3% milk must be mixed to make milk testing 5% fat?
a) 2 and 35
b) 4 and 45
c) 5 and 10
d) 6 and 12
Explanation: 2.0 parts of 40% cream when mixed with 35 parts of 3.0% milk will give 37 parts of 5% milk. Calculated using the Pearson square method.
Fat is added back to skim milk in the process of standardization.
Explanation: When standardizing dairy products, the cream and milk are first separated on a dairy line. The two elements are then mixed together again. However, not all of the original fat content is added back; only the exact level required for milk to be classified as skimmed, semi skimmed or whole.