GATE — Life Sciences (XL), Section U Food Technology · India · IITs and IISc on rotation (2026: IIT Guwahati)
Original practice questions written to the published syllabus · not past papersHandling and processing fish and shellfish: post-mortem spoilage and freshness, chilling and freezing at sea and ashore, canning, curing, smoking and drying, surimi and value-added products, and seafood safety hazards.
In the exams: GATE XE-G Section 3 (drying, canning and freezing of fish); ICAR AIEEA-PG Code 18 Unit III (fish and sea foods)
GATE — Engineering Sciences (XE), Section G Food Technology
Section 3 names drying, canning and freezing of fish. Expect conceptual items on post-mortem change, TMAO and TMA, why fish spoils faster than meat, glazing, freezer burn and protein denaturation, canned-fish defects such as struvite and blackening, and numerical-answer items on drying yield, glaze percentage, drip loss, water-phase salt and K value.
GATE — Life Sciences (XL), Section U Food Technology
Same Section 3 content as XE-G. Science graduates meet fish spoilage through microbiology (Shewanella, Photobacterium, histamine formers), biochemistry (ATP breakdown and K value, TMAO reduction, formaldehyde formation in gadoids) and protein chemistry of surimi gels.
How our questions for GATE spread across the units of Fish & Seafood Processing Technology. Difficulty: 9 easy, 16 medium, 3 hard.
| Chilling and freezing of fish | 5 | |
| Fish canning | 5 | |
| Composition of fish and shellfish | 4 | |
| Post-mortem changes and spoilage of fish | 4 | |
| Salting, drying and smoking of fish | 4 | |
| Surimi and fish mince products | 4 | |
| Freshness assessment: sensory, TVB-N, TMA and K value | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
In a fatty fish such as herring, as fat content rises through the feeding season, the water content of the flesh
C. Falls, so fat plus water stays roughly constant
Fat replaces water in the flesh of fatty fish, so the two vary inversely and their sum stays roughly constant. Fat tissue does not hold extra water, and the inverse relation is well established.
Further reading: Huss, Quality and Quality Changes in Fresh Fish (FAO FTP 348)
Fish flesh flakes easily on cooking, unlike beef, mainly because fish muscle has
C. Little, heat-labile connective tissue
Fish myotomes are separated by thin myocommata of collagen that is low in amount and heat-labile, so it gelatinises easily and the flesh separates into flakes. White fish muscle has little myoglobin, myofibrillar proteins are present, and glycogen is low.
Further reading: Huss, Quality and Quality Changes in Fresh Fish (FAO FTP 348)
Freshwater fish give low trimethylamine readings even when spoiled because they
B. Contain little TMAO
TMA comes from bacterial reduction of TMAO, which marine fish accumulate for osmoregulation and freshwater fish contain little of, so TMA is not a useful index in freshwater species. They do have spoilage bacteria, their pH is not especially low, and they contain protein.
Further reading: Huss, Quality and Quality Changes in Fresh Fish (FAO FTP 348)
In ATP breakdown in fish muscle after death, the compound responsible for the sweet, meaty taste of very fresh fish is
D. Inosine monophosphate
ATP is degraded via ADP and AMP to IMP, which gives the fresh, meaty flavour; IMP then breaks down to inosine and bitter hypoxanthine. ATP itself is gone early, and TMA is a bacterial spoilage product.
Further reading: Huss, Quality and Quality Changes in Fresh Fish (FAO FTP 348)
In chilled marine fish stored aerobically, the specific spoilage organism that reduces TMAO to TMA and produces hydrogen sulphide is
B. Shewanella putrefaciens
Shewanella putrefaciens is a cold-tolerant Gram-negative bacterium that reduces TMAO and produces H2S and other sulphur compounds in iced marine fish. Lactobacillus, Bacillus and Aspergillus are not the main spoilers of iced fish.
Further reading: Huss, Quality and Quality Changes in Fresh Fish (FAO FTP 348)
1000 g of glazed frozen shrimp weighs 850 g after the glaze is removed. The glaze, as a percentage of the glazed weight, is
A. 15.0%
Glaze = 1000 − 850 = 150 g; 150 ÷ 1000 × 100 = 15.0%. 17.6% expresses the glaze on the deglazed weight (150 ÷ 850); 85% is the net shrimp; 8.5% is a decimal slip.
Further reading: Hall (ed.), Fish Processing Technology
500 g of frozen fish fillets weigh 465 g after thawing and draining. The drip loss is
C. 7.0%
Drip = 500 − 465 = 35 g; 35 ÷ 500 × 100 = 7.0%. 7.5% divides by the thawed weight (35 ÷ 465); 93% is the retained weight; 35% treats grams as per cent.
Further reading: Hall (ed.), Fish Processing Technology
Histamine found in canned tuna was most likely formed
D. In poorly chilled raw fish
Histamine is formed by bacterial decarboxylation of histidine while raw fish is above chill temperature; it is heat-stable, so retorting does not destroy it. Heat does not form histamine, commercially sterile cans have no growing bacteria, and air does not create it.
Further reading: Hall (ed.), Fish Processing Technology
In kench salting of fish, the brine formed
B. Drains away from the fish
Kench salting stacks fish with dry salt and lets the brine drain off; pickle curing keeps the fish in its own brine. Boiling brine and vinegar are not part of kench salting.
Further reading: Hall (ed.), Fish Processing Technology
100 kg of fresh fish at 80% moisture (wet basis) is dried to 15% moisture (wet basis). The dried yield is
A. 23.5 kg
Solids = 20 kg; dried mass = 20 ÷ 0.85 = 23.5 kg. 20 kg is bone-dry solids; 18.8 kg divides 15 by 0.80; 35 kg adds the final moisture percentage to the solids.
Further reading: Hall (ed.), Fish Processing Technology
Ten here, 28 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.
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