ASRB NET — Farm Machinery & Power / Land & Water Management Engineering / Agricultural Structures & Process Engineering · India · Agricultural Scientists Recruitment Board (ICAR)
Original practice questions written to the published syllabus · not past papersUnit operations of food and milk plants: balances, fluid flow, heat exchange, thermal processing, evaporation, separation, freezing and hygienic design.
In the exams: GATE AG Section 7 (~9 marks a year 2019–26; thermal processing in all 8 papers); ICAR AICE subject 38; ICAR AIEEA-PG Unit VI; NCEES PE processing
ASRB NET — Agricultural Structures & Process Engineering
Conceptual MCQs across the whole subject: which exchanger or evaporator for which product, rheological models, the kinetic parameters, membrane separations and sanitary design.
How our questions for ASRB NET spread across the units of Food & Dairy Engineering. Difficulty: 33 easy, 16 medium, 0 hard.
| Thermal processing kinetics: D, z and F values | 5 | |
| Cleaning-in-place and sanitary design | 5 | |
| Fluid flow in food plants: pumps, pipes and rheology | 4 | |
| Pasteurisation: HTST and LTLT | 4 | |
| UHT processing and sterilisation | 4 | |
| Evaporation: single and multiple effect | 4 | |
| Centrifugation and cream separation | 4 | |
| Freezing and Plank's equation | 4 | |
| Material and energy balances | 3 | |
| Heat exchangers: plate, tubular and scraped-surface | 3 | |
| Spray and drum drying | 3 | |
| Homogenisation | 3 | |
| Filtration and membrane processes: MF, UF, NF and RO | 3 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Fouling of plate heat exchangers when milk is heated above about 70 °C is caused mainly by
B. Denatured β-lactoglobulin depositing with calcium phosphate
β-lactoglobulin unfolds and aggregates above about 70 °C and deposits with calcium phosphate, whose solubility falls as temperature rises. Lactose browning is a minor factor; fat crystallises on cold, not hot, surfaces.
Further reading: Walstra et al., Dairy Science and Technology
D is 5 min at 110 °C and 0.5 min at 120 °C. The z value is
D. 10 °C
z = (T₂ − T₁)/log(D₁/D₂) = 10/log(10) = 10 °C. 4.3 °C uses the natural log (10/2.303); 1 °C divides by the ratio 10 instead of its log; 2.2 °C divides by the difference in D (10/4.5).
Further reading: Singh and Heldman, Introduction to Food Engineering
HTST and UHT processes preserve quality better than long, lower-temperature processes of equal lethality because
A. Quality attributes have larger z values than bacterial spores
A larger z means a slower increase in rate with temperature. Raising temperature accelerates spore death (z ≈ 10 °C) much more than quality loss (z typically 25–50 °C), so short hot processes win.
Further reading: Singh and Heldman, Introduction to Food Engineering
If the milk temperature at the end of the holding tube falls below the legal set point, the
A. Flow diversion valve returns the milk to the balance tank
The recorder-controller at the holding-tube outlet actuates the flow diversion valve, sending under-processed milk back for reprocessing.
Further reading: Singh and Heldman, Introduction to Food Engineering
Compared with indirect UHT, direct steam heating typically gives
D. Milder flavour change but lower heat recovery
Near-instant heating and cooling reduce chemical change, but regeneration is limited because heat leaves with the flash vapour. Steam must be culinary quality because it contacts food.
Further reading: Singh and Heldman, Introduction to Food Engineering
Evaporators for milk operate under vacuum mainly to
C. Lower the boiling temperature and protect heat-sensitive components
Lower pressure lowers boiling point, reducing heat damage such as browning and protein denaturation, and increases the temperature difference available.
Further reading: Singh and Heldman, Introduction to Food Engineering
A solute is at 5.0 % in the feed and 0.2 % in the permeate. The observed rejection is
A. 0.96
R = 1 − C_p/C_f = 1 − 0.2/5.0 = 0.96. 0.04 is the passage (C_p/C_f). 25 is the concentration ratio C_f/C_p; 24 divides by the permeate instead of the feed ((5.0 − 0.2)/0.2).
Further reading: Singh and Heldman, Introduction to Food Engineering
Rapid freezing gives better texture in thawed fruit and vegetables than slow freezing because it forms
B. Many small ice crystals, largely inside cells
Fast freezing gives many small crystals with less cell damage and drip; slow freezing gives large extracellular crystals that rupture tissue.
Further reading: Singh and Heldman, Introduction to Food Engineering
Individually quick frozen (IQF) peas are usually produced in a
D. Fluidised-bed freezer
Upward cold air suspends small particles so each freezes separately and fast. Plate freezers suit flat blocks; scraped-surface freezers are for ice-cream mix.
Further reading: Singh and Heldman, Introduction to Food Engineering
Molybdenum-bearing AISI 316 stainless steel is chosen over 304 for some food-contact duties because it
B. Resists pitting corrosion by chlorides better
Molybdenum improves resistance to chloride pitting and crevice corrosion, useful with brines, some cleaning chemicals and salty products. It costs more and conducts heat similarly.
Further reading: Singh and Heldman, Introduction to Food Engineering
Ten here, 49 in the app. The Laisha app has every practice question we have written to ASRB NET in this subject, marked as you go, with timed papers, a jump-to-unanswered list and a certificate when you pass at 70 per cent.
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