GATE — Engineering Sciences (XE), Section G Food Technology · India · IITs and IISc on rotation (2026: IIT Guwahati)
Original practice questions written to the published syllabus · not past papersProcessing spices and herbs, extracting essential oils and oleoresins, and the technology of natural and synthetic flavours and food colours, including encapsulation and flavour stability.
In the exams: GATE XE-G Section 3 (spice; extraction of essential oils and oleoresins from spices); ICAR AIEEA-PG Code 18 Unit III (flavouring and pigment technology); ICAR AICE 35.a Unit 7
GATE — Engineering Sciences (XE), Section G Food Technology
Section 3 lists spices and extraction of essential oils and oleoresins. Expect short reasoning items on steam distillation (why oils distil below 100 °C, oil-to-water ratio), oleoresin versus essential oil, supercritical CO2 conditions, cryogenic grinding, and the active principles of the major spices; numerical-answer items on oil and oleoresin yield, drying yield and moisture balances.
GATE — Life Sciences (XL), Section U Food Technology
Same Section 3 content as XE-G. Science graduates meet the same extraction and spice-chemistry questions, often through chemistry: terpenes and phenylpropanoids, gingerol to shogaol, sinigrin and myrosinase, alliin and alliinase, Maillard and Strecker products, pigment stability with pH.
How our questions for GATE spread across the units of Spices, Herbs, Essential Oils & Flavour Technology. Difficulty: 13 easy, 22 medium, 8 hard.
| Spice processing: cleaning, drying, grinding and sterilisation | 9 | |
| Major spices: composition and active principles | 8 | |
| Essential oils: steam distillation and other extraction methods | 8 | |
| Oleoresins: solvent and supercritical CO2 extraction | 8 | |
| Cryogenic grinding | 7 | |
| Quality standards and adulteration of spices | 3 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
The pungent principle of black pepper is
B. Piperine
Piperine and related amides give black pepper its pungency. Capsaicin is the pungent principle of chilli, gingerol of fresh ginger, and eugenol is the main aroma compound of clove.
Further reading: Pruthi, Spices and Condiments
Turmeric rhizomes are boiled or steamed before drying mainly to
A. Gelatinise starch, even out the colour
Boiling or steaming softens the rhizome, gelatinises starch, distributes the yellow colour evenly and kills the rhizome, giving a uniform, hard, bright product after drying and polishing. Curcumin is not deliberately extracted into the water, curing is not a fermentation, and volatile oil removal is not the aim.
Further reading: Peter (ed.), Handbook of Herbs and Spices
The coolant most used in cryogenic grinding of spices is
B. Liquid nitrogen
Liquid nitrogen at about −196 °C cools and embrittles the spice and leaves an inert gas atmosphere. Ammonia is toxic, and brine or ice slurry would wet the product.
Further reading: Peter (ed.), Handbook of Herbs and Spices
Cryogenic grinding prevents mill clogging with oily spices such as clove mainly because
A. The fat and oil stay solid and brittle
Below the temperature at which their fat solidifies, oily spices fracture cleanly instead of smearing. Nitrogen does not dissolve or carry away the oil, and cooling does not dry the spice.
Further reading: Peter (ed.), Handbook of Herbs and Spices
Which hazard is specific to working near a cryogenic grinding line in a closed room?
C. Asphyxiation as nitrogen displaces oxygen
Evaporating liquid nitrogen expands into a large volume of gas that lowers the oxygen content of an enclosed space, so ventilation and oxygen monitors are needed. Nitrogen is inert and does not explode or release ammonia or chlorine.
Further reading: Peter (ed.), Handbook of Herbs and Spices
In a cryogenic grinding line, the screw conveyor before the mill in which liquid nitrogen is sprayed onto the spice is the
C. Precooler
The precooler, usually an insulated screw conveyor with nitrogen spray, brings the spice to grinding temperature before the mill. The cyclone separates powder from gas, the sieve classifies the product, and an airlock meters material.
Further reading: Peter (ed.), Handbook of Herbs and Spices
In steam distillation at atmospheric pressure, an oil component of molar mass 136 g/mol has a vapour pressure of 4.0 kPa and water 97.3 kPa at the boiling temperature. The mass of oil distilled per kg of water condensed is closest to
A. 0.31 kg
m_oil/m_water = (P_oil × M_oil)/(P_water × M_water) = (4.0 × 136)/(97.3 × 18) = 544/1751 = 0.31 kg per kg water. 0.041 kg ignores the molar masses (4.0/97.3); 0.0054 kg inverts the molar mass ratio; 7.6 kg multiplies by 136/18 without the pressure ratio.
Further reading: Baser and Buchbauer (eds), Handbook of Essential Oils
Folded (deterpenated) citrus oils are made because removing terpene hydrocarbons
C. Better stability and solubility
Terpene hydrocarbons such as limonene contribute little odour, oxidise easily and dissolve poorly in water and dilute alcohol; removing them concentrates the oxygenated flavour compounds and improves stability and solubility. Folding lowers, not raises, limonene.
Further reading: Baser and Buchbauer (eds), Handbook of Essential Oils
A spice gives 12% oleoresin. Taking yield as the only basis, 0.5 kg of this oleoresin carries the extractable flavour of about how much ground spice?
D. 4.2 kg
Spice = 0.5 ÷ 0.12 = 4.17 kg. 0.06 kg multiplies 0.5 by 0.12; 6.0 kg multiplies 0.5 by 12; 2.4 kg divides 12 by 5. In practice replacement ratios are confirmed by sensory and chemical comparison.
Further reading: Mukhopadhyay, Natural Extracts Using Supercritical Carbon Dioxide
A 1 g sample of ground pepper contains 50 mg of piperine. Its piperine content is
A. 5.0%
50 mg ÷ 1000 mg × 100 = 5.0%. 0.5% misplaces the decimal; 50% treats mg as per cent; 2.0% inverts and scales wrongly.
Further reading: FSSAI, DART: Detect Adulteration with Rapid Test
Ten here, 43 in the app. The Laisha app has every practice question we have written to GATE 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.
Free for ten days, then one subscription of US$10 a month. We would rather say so here than have you find it later.
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