ICAR AICE-JRF/SRF (PhD) — Agricultural Engineering subjects 38–43 · India · National Testing Agency for ICAR
Original practice questions written to the published syllabus · not past papersKeeping fruits and vegetables alive and saleable after harvest: cooling, handling, packhouses, controlled atmospheres and processing.
In the exams: GATE AG Section 6 (processing of fruits, vegetables and spices; CA/MA storage); ICAR AICE subject 41
ICAR AICE-JRF/SRF (PhD) — Processing and Food Engineering (subject 41)
PG-depth questions on respiration kinetics and MAP design equations, film permeability and beta ratio, cooling kinetics with lag factor, diffusion models of drying, thermal process lethality (F0, D, z), membrane clarification and concentration, machine vision and NIR for quality, and value-addition technologies.
How our questions for ICAR AICE-JRF/SRF spread across the units of Post-Harvest Engineering of Horticultural Crops. Difficulty: 0 easy, 33 medium, 22 hard.
| Controlled and modified atmosphere storage | 12 | |
| Respiration and ripening physiology | 7 | |
| Processing of spices and plantation crops | 7 | |
| Grading, including machine vision | 6 | |
| Minimal processing | 5 | |
| Dehydration of fruits and vegetables | 5 | |
| Pre-cooling: hydro, forced-air and vacuum cooling | 4 | |
| Juice extraction | 4 | |
| Value addition | 3 | |
| Washing, sorting and waxing | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
1-Methylcyclopropene (1-MCP) delays ripening of apples mainly by
D. binding ethylene receptors
1-MCP occupies the ethylene receptors in the tissue, blocking the ethylene response. Oxidation of ethylene is what catalytic scrubbers and permanganate do; they remove ethylene from the air but do not block its action inside the fruit.
Further reading: Kader (ed.), Postharvest Technology of Horticultural Crops (UC ANR 3311)
Cooling of large melons is described by Y = j exp(-C t) with lag factor j = 1.2 and cooling coefficient C = 0.02 per minute. The half-cooling time is about
B. 43.8 min
Set Y = 0.5: 0.5 = 1.2 exp(-0.02 t), t = ln(1.2/0.5)/0.02 = ln 2.4/0.02 = 43.8 min. Ignoring the lag (j = 1) gives 34.7 min; putting j on the wrong side gives ln(2/1.2)/0.02 = 25.5 min. A lag factor above 1 lengthens the half-cooling time. 41.6 min multiplies the unlagged 34.7 min by j.
Further reading: Thompson et al., Commercial Cooling of Fruits, Vegetables, and Flowers (UC ANR 21567)
Hot-water immersion of mango for export is primarily used as
A. a quarantine treatment against fruit fly, to a schedule set by the importing country
Hot-water treatment raises pulp temperature for a specified time to kill fruit fly eggs and larvae; the importing country's plant protection authority sets the exact schedule. It can also reduce anthracnose, but it is not a ripening step.
Further reading: Kader (ed.), Postharvest Technology of Horticultural Crops (UC ANR 3311)
Visible/near-infrared spectroscopy in a packhouse is used mainly to predict
D. soluble solids content and dry matter non-destructively
Vis-NIR spectra relate to absorbance by water, sugars and other constituents; after calibration against laboratory values they predict internal attributes such as soluble solids and dry matter. Diameter and mass are measured by cameras and load cells.
Further reading: Kader (ed.), Postharvest Technology of Horticultural Crops (UC ANR 3311)
0.5 kg of produce with respiratory quotient 1 consumes 10 mL O2/kg h in a sealed film package of area 0.12 m2. The film's CO2 permeance is 24 000 mL/(m2 day atm) and outside CO2 is negligible. The steady-state CO2 inside is about
C. 4.2%
CO2 output = O2 uptake x RQ = 0.5 x 10 x 24 = 120 mL/day. 120 = 24 000 x 0.12 x p, so p = 120/2 880 = 0.0417 atm = 4.2%. Using the O2 permeance (6 000) instead gives 16.7%. 0.17% omits the x 24 h per day; 8.3% uses only half the film area.
Further reading: Mahajan et al., MAP design literature; Kader
A breather bag and pressure relief valve are fitted to a CA room to
D. protect the gas-tight room from pressure differences caused by temperature and gas changes
A sealed room would develop pressure differences as air cools, warms or CO2 is scrubbed; the breather bag absorbs small volume changes and relief valves protect against larger ones.
Further reading: Kader (ed.), Postharvest Technology of Horticultural Crops (UC ANR 3311)
Carrot slices 6 mm thick dry from both faces in the falling-rate period with effective diffusivity 1.0 x 10^-10 m2/s. Using the first term of Fick's series solution for a slab, MR = (8/pi^2) exp(-pi^2 D t / 4L^2), the time to reach a moisture ratio of 0.2 is about
C. 14.2 h
L is the half-thickness, 3 mm. ln(0.2 / 0.8106) = -1.400. t = 1.400 x 4 x (0.003)^2 / (pi^2 x 1e-10) = 51045 s = 14.2 h. Using the full 6 mm thickness as L gives 56.7 h (four times longer); dropping the 8/pi^2 factor gives 16.3 h. 851 h is the correct time expressed in minutes and mislabelled as hours.
Further reading: Crank, The Mathematics of Diffusion; Sahay and Singh
Most spoilage bacteria cannot grow in a dried product whose water activity is below about
D. 0.90
Most bacteria need water activity above about 0.90; many yeasts and moulds grow down to about 0.80 to 0.88, and a few xerophilic moulds and osmophilic yeasts to about 0.60. 0.99 is nearly pure water, where almost everything grows, and 0.30 is far below the limit for any microbe.
Further reading: Fellows, Food Processing Technology
In apple juice clarification, ultrafiltration is used to
D. remove haze-forming colloids and microorganisms in one membrane step
UF membranes retain large molecules, colloids and microorganisms, giving a clear juice without fining and filtration steps. High concentration needs evaporation; RO reaches only moderate Brix.
Further reading: Fellows, Food Processing Technology
Sauerkraut and fermented cucumber pickles are preserved mainly by
C. lactic acid produced by salt-tolerant lactic bacteria
Salt selects lactic acid bacteria, which ferment sugars to lactic acid, lowering pH. Vinegar pickles are a different, non-fermented product.
Further reading: Srivastava and Kumar, Fruit and Vegetable Preservation: Principles and Practices
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